Dr. Melkani's Lab Home Page: Abstract Section

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J Mol Biol. 428(11):2446-61 (2016).

A Restrictive Cardiomyopathy Mutation in an Invariant Proline at the Myosin Head/Rod Junction Enhances Head Flexibility and Function, Yielding Muscle Defects in Drosophila.

Achal M, Trujillo AS, Melkani GC, Farman GP, Ocorr K, Viswanathan MC, Kaushik G, Newhard CS, Glasheen BM, Melkani A1, Suggs JA, Moore JR, Swank DM, Bodmer R, Cammarato A, Bernstein SI.

An "invariant proline" separates the myosin S1 head from its S2 tail and is proposed to be critical for orienting S1 during its interaction with actin, a process that leads to muscle contraction. Mutation of the invariant proline to leucine (P838L) caused dominant restrictive cardiomyopathy in a pediatric patient (Karam et al., Congenit. Heart Dis. 3:138-43, 2008). Here, we use Drosophila melanogaster to model this mutation and dissect its effects on the biochemical and biophysical properties of myosin, as well as on the structure and physiology of skeletal and cardiac muscles. P838L mutant myosin isolated from indirect flight muscles of transgenic Drosophila showed elevated ATPase and actin sliding velocity in vitro. Furthermore, the mutant heads exhibited increased rotational flexibility, and there was an increase in the average angle between the two heads. Indirect flight muscle myofibril assembly was minimally affected in mutant homozygotes, and isolated fibers displayed normal mechanical properties. However, myofibrils degraded during aging, correlating with reduced flight abilities. In contrast, hearts from homozygotes and heterozygotes showed normal morphology, myofibrillar arrays, and contractile parameters. When P838L was placed in trans to Mhc(5), an allele known to cause cardiac restriction in flies, it did not yield the constricted phenotype. Overall, our studies suggest that increased rotational flexibility of myosin S1 enhances myosin ATPase and actin sliding. Moreover, instability of P838L myofibrils leads to decreased function during aging of Drosophila skeletal muscle, but not cardiac muscle, despite the strong evolutionary conservation of the P838 residue.

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Science 13 March 2015: Vol. 347 no. 6227 pp. 1265-1269

Time-restricted feeding attenuates age-related cardiac decline in Drosophila.

Shubhroz Gill, Hiep D. Le1, Girish C. Melkani, Satchidananda Panda.

Circadian clocks orchestrate periods of rest or activity and feeding or fasting over the course of a 24-hour day and maintain homeostasis. To assess whether a consolidated 24-hour cycle of feeding and fasting can sustain health, we explored the effect of time-restricted feeding (TRF; food access limited to daytime 12 hours every day) on neural, peripheral, and cardiovascular physiology in Drosophila melanogaster. We detected improved sleep, prevention of body weight gain, and deceleration of cardiac aging under TRF, even when caloric intake and activity were unchanged. We used temporal gene expression profiling and validation through classical genetics to identify the TCP-1 ring complex (TRiC) chaperonin, the mitochondrial electron transport chain complexes, and the circadian clock as pathways mediating the benefits of TRF.

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J Biol Chem. 290: 29270–29280 (2015)

A Failure to Communicate MYOSIN RESIDUES INVOLVED IN HYPERTROPHIC CARDIOMYOPATHY AFFECT INTERDOMAIN INTERACTION.

Kronert WA, Melkani GC, Melkani A, Bernstein SI.

Our molecular modeling studies suggest a charge-dependent interaction between residues Glu-497 in the relay domain and Arg-712 in the converter domain of human β-cardiac myosin. To test the significance of this putative interaction, we generated transgenic Drosophila expressing indirect flight muscle myosin with charge reversal mutations in the relay (E496R) or converter (R713E). Each mutation yielded dramatic reductions in myosin Ca-ATPase activity (∼80%) as well as in basal (∼67%) and actin-activated (∼84%) Mg-ATPase activity. E496R myosin-induced in vitro actin-sliding velocity was reduced by 71% and R713E myosin permitted no actin motility. Indirect flight muscles of late pupae from each mutant displayed disrupted myofibril assembly, with adults having severely abnormal myofibrils and no flight ability. To understand the molecular basis of these defects, we constructed a putative compensatory mutant that expresses myosin with both E496R and R713E. Intriguingly, ATPase values were restored to ∼73% of wild-type and actin-sliding velocity increased to 40%. The double mutation suppresses myofibril assembly defects in pupal indirect flight muscles and dramatically reduces myofibril disruption in young adults. Although sarcomere organization is not sustained in older flies and flight ability is not restored in homozygotes, young heterozygotes fly well. Our results indicate that this charge-dependent interaction between the myosin relay and converter domains is essential to the mechanochemical cycle and sarcomere assembly. Furthermore, the same inter-domain interaction is disrupted when modeling human β-cardiac myosin heavy chain cardiomyopathy mutations E497D or R712L, implying that abolishing this salt bridge is one cause of the human disease.

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J. Biol. Chem.. 291:1763-1773 (2016)

The relay-converter interface influences hydrolysis of ATP by skeletal muscle myosin II.

Bloemink MJ, Melkani GC, Bernstein SI, Geeves MA.

The interface between relay and converter domain of muscle myosin is critical for optimal myosin performance. Using Drosophila melanogaster indirect flight muscle S1 we performed a kinetic analysis of the effect of mutations in the converter and relay domain. Introduction of a mutation (R759E) in the converter domain inhibits the steady-state ATPase of myosin S1, whereas an additional mutation in the relay domain (N509K) is able to restore the ATPase towards wild-type values. The S1- R759E construct showed little effect on most steps of the actomyosin ATPase cycle. The exception was a 25-30% reduction in the rate constant of the hydrolysis step, the step coupled to the cross-bridge recovery stroke and involving a change in conformation at the relay/converter domain interface. Significantly the double mutant restored the hydrolysis step to values similar to the wild-type myosin. Modelling the relay/converter interface suggests a possible interaction between converter residue 759 and relay residue 509 in the actin-detached conformation, which is lost in R759E but is restored in N509K/R759E. This detailed kinetic analysis of Drosophila myosin carrying the R759E mutation shows that the interface between the relay loop and converter domain is important for fine-tuning myosin kinetics, in particular ATP-binding and hydrolysis.

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J Biol Chem. 289: 12779-90 (2014)

Mapping interactions between myosin relay and converter domains that power muscle function.

Kronert WA, Melkani GC, Melkani A, Bernstein SI.

Intra-molecular communication within myosin is essential for its function as motor, but the specific amino acid residue interactions required are unexplored within muscle cells. Using Drosophila melanogaster skeletal muscle myosin, we performed a novel in vivo molecular suppression analysis to define the importance of three relay loop amino acid residues (I508, N509 and D511) in communicating with converter domain residue R759. We find that the N509K relay mutation suppresses defects in myosin ATPase, in vitro motility, myofibril stability and muscle function associated with the R759E converter mutation. Through molecular modeling we define a mechanism for this interaction and suggest why the I508K and D511K relay mutations fail to suppress R759E. Interestingly, I508K disables motor function and myofibril assembly, suggesting productive relay-converter interaction is essential for both processes. We conclude that the putative relay-converter interaction mediated by myosin residues 509 and 759 is critical for the biochemical and biophysical function of skeletal muscle myosin and the normal ultrastructural and mechanical properties of muscle.

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Rare Dis. 2: e968003 (2014)

Drosophila as a potential model to ameliorate mutant Huntington-mediated cardiac amyloidosis.

Trujillo AS, Ramos R, Bodmer R, Bernstein SI, Ocorr K, Melkani GC.

Several human diseases, including Huntington's disease (HD), are associated with the expression of mutated, misfolded, and aggregation-prone amyloid proteins. Cardiac disease is the second leading cause of death in HD, which has been mainly studied as a neurodegenerative disease that is caused by expanded polyglutamine repeats in the huntingtin protein. Since the mechanistic basis of mutant HD-induced cardiomyopathy is unknown, we established a Drosophila heart model that exhibited amyloid aggregate-induced oxidative stress, resulting in myofibrillar disorganization and physiological defects upon expression of HD-causing PolyQ expression in cardiomyocytes. Using powerful Drosophila genetic techniques, we suppressed mutant HD-induced cardiomyopathy by modulating pathways associated with folding defects and oxidative stress. In this addendum, we describe additional potential molecular players that might be associated with HD cardiac amyloidosis. Drosophila, with its high degree of conservation to the human genome and many techniques to manipulate its gene expression, will be an excellent model for the suppression of cardiac amyloidosis linked to other polyglutamine expansion repeat disorders.

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Int Rev Cell Mol Biol. 313: 103-44 (2014)

The UNC-45 myosin chaperone: from worms to flies to vertebrates.

Lee CF, Melkani GC, Bernstein SI.

UNC-45 (uncoordinated mutant number 45) is a UCS (UNC-45, CRO1, She4p) domain protein that is critical for myosin stability and function. It likely aides in folding myosin during cellular differentiation and maintenance, and protects myosin from denaturation during stress. Invertebrates have a single unc-45 gene that is expressed in both muscle and nonmuscle tissues. Vertebrates possess one gene expressed in striated muscle (unc-45b) and another that is more generally expressed (unc-45a). Structurally, UNC-45 is composed of a series of α-helices connected by loops. It has an N-terminal tetratricopeptide repeat domain that binds to Hsp90 and a central domain composed of armadillo repeats. Its C-terminal UCS domain, which is also comprised of helical armadillo repeats, interacts with myosin. In this chapter, we present biochemical, structural, and genetic analyses of UNC-45 in Caenorhabditis elegans, Drosophila melanogaster, and various vertebrates. Further, we provide insights into UNC-45 functions, its potential mechanism of action, and its roles in human disease.

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PLoS Genet. 10: e1004024 (2013)

Huntington's disease induced cardiac amyloidosis is reversed by modulating protein folding and oxidative stress pathways in the Drosophila heart.

Melkani GC, Trujillo AS, Ramos R, Bodmer R, Bernstein SI, Ocorr K.

Amyloid-like inclusions have been associated with Huntington's disease (HD), which is caused by expanded polyglutamine repeats in the Huntingtin protein. HD patients exhibit a high incidence of cardiovascular events, presumably as a result of accumulation of toxic amyloid-like inclusions. We have generated a Drosophila model of cardiac amyloidosis that exhibits accumulation of PolyQ aggregates and oxidative stress in myocardial cells, upon heart-specific expression of Huntingtin protein fragments (Htt-PolyQ) with disease-causing poly-glutamine repeats (PolyQ-46, PolyQ-72, and PolyQ-102). Cardiac expression of GFP-tagged Htt-PolyQs resulted in PolyQ length-dependent functional defects that included increased incidence of arrhythmias and extreme cardiac dilation, accompanied by a significant decrease in contractility. Structural and ultrastructural analysis of the myocardial cells revealed reduced myofibrillar content, myofibrillar disorganization, mitochondrial defects and the presence of PolyQ-GFP positive aggregates. Cardiac-specific expression of disease causing Poly-Q also shortens lifespan of flies dramatically. To further confirm the involvement of oxidative stress or protein unfolding and to understand the mechanism of PolyQ induced cardiomyopathy, we co-expressed expanded PolyQ-72 with the antioxidant superoxide dismutase (SOD) or the myosin chaperone UNC-45. Co-expression of SOD suppressed PolyQ-72 induced mitochondrial defects and partially suppressed aggregation as well as myofibrillar disorganization. However, co-expression of UNC-45 dramatically suppressed PolyQ-72 induced aggregation and partially suppressed myofibrillar disorganization. Moreover, co-expression of both UNC-45 and SOD more efficiently suppressed GFP-positive aggregates, myofibrillar disorganization and physiological cardiac defects induced by PolyQ-72 than did either treatment alone. Our results demonstrate that mutant-PolyQ induces aggregates, disrupts the sarcomeric organization of contractile proteins, leads to mitochondrial dysfunction and increases oxidative stress in cardiomyocytes leading to abnormal cardiac function. We conclude that modulation of both protein unfolding and oxidative stress pathways in the Drosophila heart model can ameliorate the detrimental PolyQ effects, thus providing unique insights into the genetic mechanisms underlying amyloid-induced cardiac failure in HD patients.

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J Mol Biol. 416: 543-557 (2012)

Alternative relay and converter domains tune native muscle myosin isoform function in Drosophila.

Kronert WA, Melkani GC, Melkani A, Bernstein SI.

Myosin isoforms help define muscle-specific contractile and structural properties. Alternative splicing of myosin heavy chain gene transcripts in Drosophila melanogaster yields muscle-specific isoforms and highlights alternative domains that fine-tune myosin function. To gain insight into how native myosin is tuned, we expressed three embryonic myosin isoforms in indirect flight muscles lacking endogenous myosin. These isoforms differ in their relay and/or converter domains. We analyzed isoform-specific ATPase activities, in vitro actin motility and myofibril structure/stability. We find that dorsal acute body wall muscle myosin (EMB-9c11d) shows a significant increase in MgATPase V(max) and actin sliding velocity, as well as abnormal myofibril assembly compared to cardioblast myosin (EMB-11d). These properties differ as a result of alternative exon-9-encoded relay domains that are hypothesized to communicate signals among the ATP-binding pocket, actin-binding site and the converter domain. Further, EMB-11d shows significantly reduced levels of basal Ca- and MgATPase as well as MgATPase V(max) compared to embryonic body wall muscle isoform (EMB) (expressed in a multitude of body wall muscles). EMB-11d also induces increased actin sliding velocity and stabilizes myofibril structure compared to EMB. These differences arise from exon-11-encoded alternative converter domains that are proposed to reposition the lever arm during the power and recovery strokes. We conclude that relay and converter domains of native myosin isoforms fine-tune ATPase activity, actin motility and muscle ultrastructure. This verifies and extends previous studies with chimeric molecules and indicates that interactions of the relay and converter during the contractile cycle are key to myosin-isoform-specific kinetic and mechanical functions.

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Biosci Rep. 2012 Jun;32(3):299-303 (2012)

Interaction of oxidized chaperonin GroEL with an unfolded protein at low temperatures.

Melkani GC, Sielaff R, Zardeneta G, Mendoza JA.

The chaperonin GroEL binds to non-native substrate proteins via hydrophobic interactions, preventing their aggregation, which is minimized at low temperatures. In the present study, we investigated the refolding of urea-denatured rhodanese at low temperatures, in the presence of ox-GroEL (oxidized GroEL), which contains increased exposed hydrophobic surfaces and retains its ability to hydrolyse ATP. We found that ox-GroEL could efficiently bind the urea-unfolded rhodanese at 40C, without requiring excess amount of chaperonin relative to normal GroEL (i.e. non-oxidized). The release/reactivation of rhodanese from GroEL was minimal at 40C, but was found to be optimal between 22 and 370C. It was found that the loss of the ATPase activity of ox-GroEL at 40C prevented the release of rhodanese from the GroEL-rhodanese complex. Thus ox-GroEL has the potential to efficiently trap recombinant or non-native proteins at 40C and release them at higher temperatures under appropriate conditions.

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Mol Biol Cell. 23:2057-65 (2012).

Expression of the inclusion body myopathy 3 mutation in Drosophila depresses myosin function and stability and recapitulates muscle inclusions and weakness.

Wang Y, Melkani GC, Suggs JA, Melkani A, Kronert WA, Cammarato A, Bernstein SI.

Hereditary myosin myopathies are characterized by variable clinical features. Inclusion body myopathy 3 (IBM-3) is an autosomal dominant disease associated with a missense mutation (E706K) in the myosin heavy chain IIa gene. Adult patients experience progressive muscle weakness. Biopsies reveal dystrophic changes, rimmed vacuoles with cytoplasmic inclusions, and focal disorganization of myofilaments. We constructed a transgene encoding E706K myosin and expressed it in Drosophila (E701K) indirect flight and jump muscles to establish a novel homozygous organism with homogeneous populations of fast IBM-3 myosin and muscle fibers. Flight and jump abilities were severely reduced in homozygotes. ATPase and actin sliding velocity of the mutant myosin were depressed >80% compared with wild-type myosin. Light scattering experiments and electron microscopy revealed that mutant myosin heads bear a dramatic propensity to collapse and aggregate. Thus E706K (E701K) myosin appears far more labile than wild-type myosin. Furthermore, mutant fly fibers exhibit ultrastructural hallmarks seen in patients, including cytoplasmic inclusions containing aberrant proteinaceous structures and disorganized muscle filaments. Our Drosophila model reveals the unambiguous consequences of the IBM-3 lesion on fast muscle myosin and fibers. The abnormalities observed in myosin function and muscle ultrastructure likely contribute to muscle weakness observed in our flies and patients.

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Methods. 56:25-32. (2012)

Transgenic expression and purification of myosin isoforms using the Drosophila melanogaster indirect flight muscle system.

Caldwell JT, Melkani GC, Huxford T, Bernstein SI.

Biophysical and structural studies on muscle myosin rely upon milligram quantities of extremely pure material. However, many biologically interesting myosin isoforms are expressed at levels that are too low for direct purification from primary tissues. Efforts aimed at recombinant expression of functional striated muscle myosin isoforms in bacterial or insect cell culture have largely met with failure, although high level expression in muscle cell culture has recently been achieved at significant expense. We report a novel method for the use of strains of the fruit fly Drosophila melanogaster genetically engineered to produce histidine-tagged recombinant muscle myosin isoforms. This method takes advantage of the single muscle myosin heavy chain gene within the Drosophila genome, the high level of expression of accessible myosin in the thoracic indirect flight muscles, the ability to knock out endogenous expression of myosin in this tissue and the relatively low cost of fruit fly colony production and maintenance. We illustrate this method by expressing and purifying a recombinant histidine-tagged variant of embryonic body wall skeletal muscle myosin II from an engineered fly strain. The recombinant protein shows the expected ATPase activity and is of sufficient purity and homogeneity for crystallization. This system may prove useful for the expression and isolation of mutant myosins associated with skeletal muscle diseases and cardiomyopathies for their biochemical and structural characterization.

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J Biol Chem. 286:28435-28443 (2011)

Two Drosophila myosin transducer mutants with distinct cardiomyopathies have divergent ADP and actin affinities.

Bloemink M.J., Melkani G.C., Dambacher C.M., Bernstein S.I., Geeves M.A.

Two Drosophila myosin II point mutations (D45 and Mhc5) generate Drosophila cardiac phenotypes that are similar to dilated or restrictive human cardiomyopathies. Our homology models suggest the mutations (A261T in D45, G200D in Mhc5) could stabilize (D45) or destabilize (Mhc5) loop 1 of myosin, a region known to influence ADP release. To gain insight into the molecular mechanism that causes the cardiomyopathic phenotypes to develop, we determined whether kinetic properties of the mutant molecules have been altered. We used myosin subfragment 1 (S1) carrying either of the two mutations (S1A261T and S1G200D) from the indirect flight muscles of Drosophila. The kinetic data show that the two point mutations have an opposite effect on the enzymatic activity of S1. S1A261T is less active (reduced ATPase, higher ADP affinity for S1 and actoS1 and reduced ATP-induced dissociation of acto-S1) whereas S1G200D shows increased enzymatic activity (enhanced ATPase, reduced ADP affinity for both S1 and actoS1). The opposite changes in the myosin properties are consistent with the induced cardiac phenotypes for S1A261T (dilated) and S1G200D (restrictive). Our results provide novel insights into the molecular mechanisms that cause different cardiomyopathy phenotypes for these mutants. In addition we report that S1A261T weakens the affinity of S1.ADP for actin while S1G200D increases it. This may account for the suppression (A261T) or enhancement (G200D) of the skeletal muscle hypercontraction phenotype induced by the troponin I held-up2 mutation in Drosophila.

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PLoS One 6: e22579 (2011)

The UNC-45 Chaperone Is Critical for Establishing Myosin-Based Myofibrillar Organization and Cardiac Contractility in the Drosophila Heart Model.

Melkani, G. C., R. Bodmer, K. Ocorr and S.I. Bernstein

UNC-45 is a UCS (UNC-45/CRO1/She4P) class chaperone necessary for myosin folding and/or accumulation, but its requirement for maintaining cardiac contractility has not been explored. Given the prevalence of myosin mutations in eliciting cardiomyopathy, chaperones like UNC-45 are likely to be equally critical in provoking or modulating myosin-associated cardiomyopathy. Here, we used the Drosophila heart model to examine its role in cardiac physiology, in conjunction with RNAi-mediated gene silencing specifically in the heart in vivo. Analysis of cardiac physiology was carried out using high-speed video recording in conjunction with movement analysis algorithms. unc-45 knockdown resulted in severely compromised cardiac function in adults as evidenced by prolonged diastolic and systolic intervals, and increased incidence of arrhythmias and extreme dilation; the latter was accompanied by a significant reduction in muscle contractility. Structural analysis showed reduced myofibrils, myofibrillar disarray, and greatly decreased cardiac myosin accumulation. Cardiac unc-45 silencing also dramatically reduced life-span. In contrast, third instar larval and young pupal hearts showed mild cardiac abnormalities, as severe cardiac defects only developed during metamorphosis. Furthermore, cardiac unc-45 silencing in the adult heart (after metamorphosis) led to less severe phenotypes. This suggests that UNC-45 is mostly required for myosin accumulation/folding during remodeling of the forming adult heart. The cardiac defects, myosin deficit and decreased life-span in flies upon heart-specific unc-45 knockdown were significantly rescued by UNC-45 over-expression. Our results are the first to demonstrate a cardiac-specific requirement of a chaperone in Drosophila, suggestive of a critical role of UNC-45 in cardiomyopathies, including those associated with unfolded proteins in the failing human heart. The dilated cardiomyopathy phenotype associated with UNC-45 deficiency is mimicked by myosin knockdown suggesting that UNC-45 plays a crucial role in stabilizing myosin and possibly preventing human cardiomyopathies associated with functional deficiencies of myosin.

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J. Cell Sci. 24: 699-705. (2011)

Drosophila UNC-45 accumulates in embryonic blastoderm and in muscles and is essential for muscle myosin stability.

Lee, C. F., G. C. Melkani, Q. Yu, J. A. Suggs, W. A. Kronert, Y. Suzuki, L. Hipolito, M. G. Price, H. F. Epstein and S. I. Bernstein

UNC-45 is a chaperone that facilitates folding of myosin motor domains. We have used Drosophila melanogaster to investigate the role of UNC-45 in muscle development and function. Drosophila UNC-45 (dUNC-45) is expressed at all developmental stages. It colocalizes with non-muscle myosin in embryonic blastoderm of 2-hour-old embryos. At 14 hours, it accumulates most strongly in embryonic striated muscles, similarly to muscle myosin. dUNC-45 localizes to the Z-discs of sarcomeres in third instar larval body-wall muscles. We produced a dunc-45 mutant in which zygotic expression is disrupted. This results in nearly undetectable dUNC-45 levels in maturing embryos as well as late embryonic lethality. Muscle myosin accumulation is robust in dunc-45 mutant embryos at 14 hours. However, myosin is dramatically decreased in the body-wall muscles of 22-hour-old mutant embryos. Furthermore, electron microscopy showed only a few thick filaments and irregular thick-thin filament lattice spacing. The lethality, defective protein accumulation, and ultrastructural abnormalities are rescued with a wild-type dunc-45 transgene, indicating that the mutant phenotypes arise from the dUNC-45 deficiency. Overall, our data indicate that dUNC-45 is important for myosin accumulation and muscle function. Furthermore, our results suggest that dUNC-45 acts post-translationally for proper myosin folding and maturation.

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J. Mol. Biol. 398: 625-632. (2010)

Mutating the converter-relay interface of Drosophila myosin perturbs ATPase activity, actin motility, myofibril stability and flight ability.

Kronert, W. A., G. C. Melkani, A. Melkani and S. I. Bernstein.

We used an integrative approach to probe the significance of the interaction between the relay loop and converter domain of the myosin molecular motor from Drosophila melanogaster indirect flight muscle. During the myosin mechanochemical cycle, ATP-induced twisting of the relay loop is hypothesized to reposition the converter, resulting in cocking of the contiguous lever arm into the pre-power stroke configuration. The subsequent movement of the lever arm through its power stroke generates muscle contraction by causing myosin heads to pull on actin filaments. We generated a transgenic line expressing myosin with a mutation in the converter domain (R759E) at a site of relay loop interaction. Molecular modeling suggests that the interface between the relay loop and converter domain of R759E myosin would be significantly disrupted during the mechanochemical cycle. The mutation depressed calcium as well as basal and actin-activated MgATPase (V(max)) by approximately 60% compared to wild-type myosin, but there is no change in apparent actin affinity (K(m)). While ATP or AMP-PNP (adenylyl-imidodiphosphate) binding to wild-type myosin subfragment-1 enhanced tryptophan fluorescence by approximately 15% or approximately 8%, respectively, enhancement does not occur in the mutant. This suggests that the mutation reduces lever arm movement. The mutation decreases in vitro motility of actin filaments by approximately 35%. Mutant pupal indirect flight muscles display normal myofibril assembly, myofibril shape, and double-hexagonal arrangement of thick and thin filaments. Two-day-old fibers have occasional "cracking" of the crystal-like array of myofilaments. Fibers from 1-week-old adults show more severe cracking and frayed myofibrils with some disruption of the myofilament lattice. Flight ability is reduced in 2-day-old flies compared to wild-type controls, with no upward mobility but some horizontal flight. In 1-week-old adults, flight capability is lost. Thus, altered myosin function permits myofibril assembly, but results in a progressive disruption of the myofilament lattice and flight ability. We conclude that R759 in the myosin converter domain is essential for normal ATPase activity, in vitro motility and locomotion. Our results provide the first mutational evidence that intramolecular signaling between the relay loop and converter domain is critical for myosin function both in vitro and in muscle.

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Biochem. Biophys. Res. Comm. 396: 317-322. (2010)

Drosophila UNC-45 prevents heat-induced aggregation of skeletal muscle myosin and facilitates refolding of citrate synthase.

Melkani, G. C., C. F. Lee, A. Cammarato and S. I. Bernstein.

UNC-45 belongs to the UCS (UNC-45, CRO1, She4p) domain protein family, whose members interact with various classes of myosin. Here we provide structural and biochemical evidence that Escherichia coli-expressed Drosophila UNC-45 (DUNC-45) maintains the integrity of several substrates during heat-induced stress in vitro. DUNC-45 displays chaperone function in suppressing aggregation of the muscle myosin heavy meromyosin fragment, the myosin S-1 motor domain, alpha-lactalbumin and citrate synthase. Biochemical evidence is supported by electron microscopy, which reveals the first structural evidence that DUNC-45 prevents inter- or intra-molecular aggregates of skeletal muscle heavy meromyosin caused by elevated temperatures. We also demonstrate for the first time that UNC-45 is able to refold a denatured substrate, urea-unfolded citrate synthase. Overall, this in vitro study provides insight into the fate of muscle myosin under stress conditions and suggests that UNC-45 protects and maintains the contractile machinery during in vivo stress.

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J Mol Biol. 2009 389:707-721.

Alternative exon 9-encoded relay domains affect more than one communication pathway in the Drosophila myosin head.

Bloemink M. J., C. M. Dambacher, A. F. Knowles , G. C. Melkani, M. A. Geeves and S. I. Bernstein.

We investigated the biochemical and biophysical properties of one of the four alternative regions within the Drosophila myosin catalytic domain: the relay domain encoded by exon 9. This domain of the myosin head transmits conformational changes in the nucleotide-binding pocket to the converter domain, which is crucial to coupling catalytic activity with mechanical movement of the lever arm. To study the function of this region, we used chimeric myosins (IFI-9b and EMB-9a), which were generated by exchange of the exon 9-encoded domains between the native embryonic body wall (EMB) and indirect flight muscle isoforms (IFI). Kinetic measurements show that exchange of the exon 9-encoded region alters the kinetic properties of the myosin S1 head. This is reflected in reduced values for ATP-induced actomyosin dissociation rate constant (K(1)k(+2)) and ADP affinity (K(AD)), measured for the chimeric constructs IFI-9b and EMB-9a, compared to wild-type IFI and EMB values. Homology models indicate that, in addition to affecting the communication pathway between the nucleotide-binding pocket and the converter domain, exchange of the relay domains between IFI and EMB affects the communication pathway between the nucleotide-binding pocket and the actin-binding site in the lower 50-kDa domain (loop 2). These results suggest an important role of the relay domain in the regulation of actomyosin cross-bridge kinetics.

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Biochem Biophys Res Commun. 2008 Apr 11;368(3):625-30.

Divalent cations stabilize GroEL under conditions of oxidative stress.

Melkani GC, Sielaff RL, Zardeneta G, Mendoza JA.

The divalent cations Mg(2+), Mn(2+), Zn(2+), Ca(2+), and Ni(2+) were found to protect against proteolysis a form of GroEL (ox-GroEL) prepared by exposing GroEL for 16h to 6mM hydrogen peroxide (H(2)O(2)). K(+) and other monovalent cations did not have any effect. Divalent cations also induced a conformational change of ox-GroEL that led to the decrease of its large exposed hydrophobic surfaces (exposed with H(2)O(2)). Ox-GroEL incubated with a divalent cation behaved like N-GroEL in that it could transiently interact with H(2)O(2)-inactivated rhodanese (ox-rhodanese), whereas ox-GroEL alone could strongly interact with ox-rhodanese. Although, ox-GroEL incubated with a divalent cation could not recover the ATPase activity (66%) lost with H(2)O(2), it could facilitate the reactivation of ox-rhodanese (>86% of active rhodanese recovered), without requiring ATP or the co-chaperonin, GroES. This is the first report to demonstrate a role for the divalent cations on the structure and function of ox-GroEL.

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J. Mol. Biol. 2006 358: 635-645.

alphaB-Crystallin maintains skeletal muscle myosin enzymatic activity and prevents its aggregation under heat-shock stress.

Melkani, G. C., A. Cammarato and S. I. Bernstein

Here, we provide functional and direct structural evidence that alphaB-crystallin, a member of the small heat-shock protein family, suppresses thermal unfolding and aggregation of the myosin II molecular motor. Chicken skeletal muscle myosin was thermally unfolded at heat-shock temperature (43 degrees C) in the absence and in the presence of alphaB-crystallin. The ATPase activity of myosin at 25 degrees C was used as a parameter to monitor its unfolding. Myosin retained only 65% and 8% of its ATPase activity when incubated at heat-shock temperature for 15min and 30min, respectively. However, 84% and 58% of the myosin ATPase activity was maintained when it was incubated with alphaB-crystallin under the same conditions. Furthermore, actin-stimulated ATPase activity of myosin was reduced by approximately 90%, when myosin was thermally unfolded at 43 degrees C for 30min, but was reduced by only approximately 42% when it was incubated with alphaB-crystallin under the same conditions. Light-scattering assays and bound thioflavin T fluorescence indicated that myosin aggregates when incubated at 43 degrees C for 30min, while alphaB-crystallin suppressed this thermal aggregation. Photo-labeled bis-ANS alphaB-crystallin fluorescence studies confirmed the transient interaction of alphaB-crystallin with myosin. These findings were further supported by electron microscopy of rotary shadowed molecules. This revealed that approximately 94% of myosin molecules formed inter and intra-molecular aggregates when incubated at 43 degrees C for 30min. alphaB-Crystallin, however, protected approximately 48% of the myosin molecules from thermal aggregation, with protected myosin appearing identical to unheated molecules. These results are the first to show that alphaB-crystallin maintains myosin enzymatic activity and prevents the aggregation of the motor under heat-shock conditions. Thus, alphaB-crystallin may be critical for nascent myosin folding, promoting myofibrillogenesis, maintaining cytoskeletal integrity and sustaining muscle performance, since heat-shock temperatures can be produced during multiple stress conditions or vigorous exercise.

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Biochem Biophys Res Commun. 2006 Aug 25;347(2):534-9

Protection of GroEL by its methionine residues against oxidation by hydrogen peroxide.

Melkani GC, Kestetter J, Sielaff R, Zardeneta G, Mendoza JA.

GroEL undergoes an important functional and structural transition when oxidized with hydrogen peroxide (H2O2) concentrations between 15 and 20mM. When GroEL was incubated for 3h with 15 mM H2O2, it retained its quaternary structure, chaperone and ATPase activities. Under these conditions, GroEL's cysteine and tyrosine residues remained intact. However, all the methionine residues of the molecular chaperone were oxidized to the corresponding methionine-sulfoxides under these conditions. The oxidation of the methionine residues was verified by the inability of cyanogen bromide to cleave at the carboxyl side of the modified methionine residues. The role for the proportionately large number (23) of methionine residues in GroEL has not been identified. Methionine residues have been reported to have an antioxidant activity in proteins against a variety of oxidants produced in biological systems including H2O2. The carboxyl-terminal domain of GroEL is rich in methionine residues and we hypothesized that these residues are involved in the protection of GroEL's functional structure by scavenging H2O2. When GroEL was further incubated for the same time, but with increasing concentrations of H2O2 (>15 mM), the oxidation of GroEL's cysteine residues and a significant decrease of the tyrosine fluorescence due to the formation of dityrosines were observed. Also, at these higher concentrations of H2O2, the inability of GroEL to hydrolyze ATP and to assist the refolding of urea-unfolded rhodanese was observed.

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Int J Biochem Cell Biol. 2005 Jul;37(7):1375-85.

On the chaperonin activity of GroEL at heat-shock temperature.

Melkani GC, Zardeneta G, Mendoza JA.

The studies of GroEL, almost exclusively, have been concerned with the function of the chaperonin under non-stress conditions, and little is known about the role of GroEL during heat shock. Being a heat shock protein, GroEL deserves to be studied under heat shock temperature. As a model for heat shock in vitro, we have investigated the interaction of GroEL with the enzyme rhodanese undergoing thermal unfolding at 43 degrees C. GroEL interacted strongly with the unfolding enzyme forming a binary complex. Active rhodanese (82%) could be recovered by releasing the enzyme from GroEL after the addition of several components, e.g. ATP and the co-chaperonin GroES. After evaluating the stability of the GroEL-rhodanese complex, as a function of the percentage of active rhodanese that could be released from GroEL with time, we found that the complex had a half-life of only one and half-hours at 43 degrees C; while, it remained stable at 25 degrees C for more than 2 weeks. Interestingly, the GroEL-rhodanese complex remained intact and only 13% of its ATPase activity was lost during its incubation at 43 degrees C. Further, rhodanese underwent a conformational change over time while it was bound to GroEL at 43 degrees C. Overall, our results indicated that the inability to recover active enzyme at 43 degrees C from the GroEL-rhodanese complex was not due to the disruption of the complex or aggregation of rhodanese, but rather to the partial loss of its ATPase activity and/or to the inability of rhodanese to be released from GroEL due to a conformational change.

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Front Biosci. 2004 Jan 1;9:724-31.

Oxidized GroEL can function as a chaperonin.

Melkani GC, Zardeneta G, Mendoza JA.

Here, we report on the facilitated reactivation (85%) of oxidatively inactivated rhodanese by an oxidized form of the molecular chaperone GroEL (ox-GroEL). Reactivation by ox-GroEL required a reductant, and the enzyme substrate, sodium thiosulfate. Also, we found that ox-GroEL formed a complex with oxidatively inactivated rhodanese as shown by differential centrifugation and fluorescence spectroscopy. Ox-GroEL was obtained upon incubation of native GroEL for 16 h with 5 mM hydrogen peroxide. Under these conditions, GroEL was shown to retain its quaternary and secondary structures, but it displayed an increased exposure of hydrophobic surfaces as detected with 1,1'-bis(4-anilino) naphthalene-5,5'-disulfonic acid (bisANS) fluorescence. Additionally, ox-GroEL was significantly more sensitive towards proteolysis with trypsin compared to the native form of the protein. The oxidatively inactivated form of rhodanese, also had an increased exposure of hydrophobic surfaces, as previously reported. Thus, the proteins binding appeared to be mediated by hydrophobic interactions. Unlike in prior reactivation studies that involved native GroEL or alpha-crystallin, we have clearly shown that an oxidized form of GroEL can function as a molecular chaperone in the reactivation of oxidatively inactivated rhodanese suggesting that GroEL retains the ability to protect proteins during oxidative stress.

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Int J Biochem Cell Biol. 2004 Mar;36(3):505-18.

Hydrogen peroxide induces the dissociation of GroEL into monomers that can facilitate the reactivation of oxidatively inactivated rhodanese.

Melkani GC, McNamara C, Zardeneta G, Mendoza JA.

Although, several studies have been reported on the effects of oxidants on the structure and function of other molecular chaperones, no reports have been made so far for the chaperonin GroEL. The ability of GroEL to function under oxidative stress was investigated in this report by monitoring the effects of hydrogen peroxide (H(2)O(2)) on the structure and refolding activity of this protein. Using fluorescence spectroscopy and light scattering, we observed that GroEL showed increases in exposed hydrophobic sites and changes in tertiary and quaternary structure. Differential sedimentation, gel electrophoresis, and circular dichroism showed that H(2)O(2) treated GroEL underwent irreversible dissociation into monomers with partial loss of secondary structure. Relative to other proteins, GroEL was found to be highly resistant to oxidative damage. Interestingly, GroEL monomers produced under these conditions can facilitate the reactivation of H(2)O(2)-inactivated rhodanese but not urea-denatured rhodanese. Recovery of approximately 84% active rhodanese was obtained with either native or oxidized GroEL in the absence of GroES or ATP. In comparison, urea-denatured GroEL, BSA and the refolding mixture in the absence of proteins resulted in the recovery of 72, 50, and 49% rhodanese activity, respectively. Previous studies have shown that GroEL monomers can reactivate rhodanese. Here, we show that oxidized monomeric GroEL can reactivate oxidized rhodanese suggesting that GroEL retains the ability to protect proteins during oxidative stress.

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Biometals. 2003 Sep;16(3):479-84.

The ATPase activity of GroEL is supported at high temperatures by divalent cations that stabilize its structure.

Melkani GC, Zardeneta G, Mendoza JA.

Previously, we reported that the ATPase activity of GroEL that requires potassium and magnesium was highly temperature dependent in the 25-60 degrees C range. Here, we report that the monovalent cations, rubidium and ammonium were able to fully substitute for potassium; while the divalent cations manganese, cobalt, and nickel supported the ATPase activity of GroEL albeit to a lesser degree than magnesium. ATPase activities with manganese, cobalt, and nickel were 64%, 41%, and 29%, respectively, of the maximum activity (100%) when utilizing magnesium. Interestingly, the ability of all the cations to support the GroEL ATPase activity was somewhat consistent over the entire 25-60 degrees C range. Maximum ATPase activities were observed at 49 degrees C. Here, the influence of these cations on the thermal denaturation of GroEL was also monitored using bisANS binding as an indication of the exposure of hydrophobic surfaces during thermal denaturation of GroEL. Maximum exposure of hydrophobic surfaces on GroEL alone or in the presence of each of the monovalent cations was determined to occur at 65 degrees C. However, the maximum exposure of hydrophobic surfaces on GroEL in the presence of magnesium, manganese, cobalt or nickel was found to occur at 71 degrees C indicating that GroEL is significantly stabilized against thermal denaturation by these divalent cations.

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Indian J Biochem Biophys. 2002 Dec;39(6):410-8.

Synthesis, conformation and vibrational dynamics of the peptide -Ser-Cys-Lys-Leu-Asp-Phe-, a fragment of apolipoprotein B.

Srivastava S, Srivastava S, Melkani GC, Singh S, Gupta VD, Vijai Prakash G.

The collective normal modes of the hexapeptide -Ser-Cys-Lys-Leu-Asp-Phe-, a fragment of apolipoprotein B (apo B), have been obtained. They reflect the dynamic nature and are atleast partly responsible for energy input in autolytic activity. Further, on energetic considerations based on the measurements reported by Sim & Sim, it has been shown that of the two such fragments only one induces autolysis, while the other remains anchored to the coated pit.

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Biochem Biophys Res Commun. 2002 Jun 21;294(4):893-9.

GroEL interacts transiently with oxidatively inactivated rhodanese facilitating its reactivation.

Melkani GC, Zardeneta G, Mendoza JA.

When the enzyme rhodanese was inactivated with hydrogen peroxide (H(2)O(2)), it underwent significant conformational changes, leading to an increased exposure of hydrophobic surfaces. Thus, this protein seemed to be an ideal substrate for GroEL, since GroEL uses hydrophobic interactions to bind to its substrate polypeptides. Here, we report on the facilitated reactivation (86%) of H(2)O(2)-inactivated rhodanese by GroEL alone. Reactivation by GroEL required a reductant and the enzyme substrate, but not GroES or ATP. Further, we found that GroEL interacted weakly and/or transiently with H(2)O(2)-inactivated rhodanese. A strong interaction with rhodanese was obtained when the enzyme was pre-incubated with urea, indicating that exposure of hydrophobic surfaces alone on oxidized rhodanese was not sufficient for the formation of a strong complex and that a more unfolded structure of rhodanese was required to interact strongly with GroEL. Unlike prior studies that involved denaturation of rhodanese through chemical or thermal means, we have clearly shown that GroEL can function as a molecular chaperone in the reactivation of an oxidatively inactivated protein. Additionally, the mechanism for the GroEL-facilitated reactivation of rhodanese shown here appears to be different than that for the chaperonin-assisted folding of chemically unfolded polypeptides in which a nucleotide and sometimes GroES is required.

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J Assoc Physicians India. 1999 Dec;47(12):1157-60.

Lipoprotein(a) and coronary heart disease in Indian population.

Singh S, Dwivedi S, Melkani GC, Rani C, Gaur SP, Mandal SK, Mahua J.

OBJECTIVE: Present study was undertaken to evaluate the role of lipoprotein(a) in coronary heart disease (CHD) patients and its relationship with other established risk factors.

METHODS: Blood samples of 67 control patients (non-cardiovascular problems) and 222 CHD patients (less or = 4 weeks post myocardial infarction) were analyzed. Lipoprotein(a) was measured in serum samples by enzyme-linked immunosorbent assay utilizing rabbit polyclonal antibodies against purified human Lp(a). Step-wise linear discriminant analysis was used to find the important parameters to discriminate CHD and non-CHD subjects.

RESULTS: The LDL to HDL cholesterol ratio (p less 0.01) and serum level of lipoprotein(a) (p less 0.01) were significantly higher in CHD patients. Levels of lipoprotein(a) were found to be higher in females compared to males (p less 0.01). Positive family history of CHD did not show significant difference in Lp(a) levels. Lp(a) level in CHD patients with positive family history of NIDDM and hypertension was higher than in with negative family history.

CONCLUSION: Clinical significance of serum level of Lp(a) and albumin in determining the risk of CHD has been observed. Lp(a) alone could correctly discriminate a CHD individual from a control subjects by 95%. Estimating of Lp(a) together with albumin provided 99% correct discrimination between control and CHD patients. These results also suggest that Lp(a) together with malnutrition could be responsible for the increased incidence of CHD in Indians. It is also indicated that in females atherothrombogenic potential of lipoprotein(a) remains suppressed before menopause but after this stage women lose this advantage.

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Indian J Biochem Biophys. 1997 Dec;34(6):512-7.

Oxidative stress and metabolic control in non-insulin dependent diabetes mellitus.

Singh S, Melkani GC, Rani C, Gaur SP, Agrawal V, Agrawal CG.

The aim of this study was to evaluate conjugated dienes in subjects with non-insulin-dependent diabetes mellitus (NIDDM) and its metabolic control. To achieve good metabolic control in addition to dietary management oral hypoglycemic agents such as glibenclamide, gliclazide and metformin were given to patients. Human plasma low-density lipoproteins (LDL) were delipidised and triglycerides (LDL-TG) and cholesterol esters (LDL-CE) were separated. Conjugated dienes in LDL-TG and LDL-CE of subjects with NIDDM (n = 90) and normal glucose tolerance (NGT) (n = 30) were measured using second derivative of uv absorption spectrum. Hypoglycemic agents lowered substantially concentration of cis, trans (c, t) and trans, trans (t, t) conjugated dienes in LDL-CE and LDL-TG. The duration of NIDDM has shown significant correlation (p less 0.001) with conjugated dienes in LDL-TG. Concentration of c, t and t, t-conjugated dienes in LDL-CE and LDL-TG were found significantly higher in subjects with NIDDM than NGT (p less 0.001). In conclusion, NIDDM, status of metabolic control and duration of diabetes have strong positive relation with oxidative stress.

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Note: Entrez Medline entries for a particular Author name may correspond with multiple authors with the same initials. Also, the list is limited to entries stored in the Entrez Medline Database and may not accurately reflect the true number of publications. You may also read the abstracts to the publications from this inquire.


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