We will use an integrative and multidisciplinary approach to investigate how the S1 head domain of the myosin heavy chain (MHC) protein drives muscle function. Myosin is the molecular motor of muscle and the major component of myofibrillar thick filaments. Its ATP-dependent interaction with actin-containing thin filaments powers muscle contraction. Our studies use the model organism Drosophila melanogaster, which has a single muscle Mhc gene but produces multiple forms of the protein (isoforms) by alternative RNA splicing. Using MHC null mutants in conjunction with germline transformation, we express engineered versions of the protein and employ them to test basic and novel hypotheses that predict structural, biochemical, fiber mechanical, physiological and locomotory properties imparted by specific myosin domains and amino acid residues. An innovative aspect of our system is that functions will be tested in vitro, in skeletal and cardiac muscle and in intact organisms. Therefore, we can determine directly and to what degree a specific biochemical property defines a physiological or locomotory characteristic. To this end, we will utilize a battery of in vitro and in vivo assays: ATPase, actin and nucleotide affinity, in vitro motility, x-ray crystallography, molecular modeling, electron microscopy, isolated fiber mechanics, video-based cardiac imaging and organismal locomotion.
Our first aim i s to elucidate the role of a critical communication element of the myosin motor called the relay domain. We will determine the importance of specific transient interactions of key amino acid residues of the relay that we hypothesize to interact with the converter domain or with the SH1-SH2 helix region during the mechanochemical cycle. For this, we will combine the transgenic approach with classical genetics to introduce and suppress mutations.
Our second aim will test predicted isoform-specific interactions during the mechanochemical cycle. To this end, we will exploit the Drosophila system to express flight and embryonic muscle myosin isoforms that will be crystallized and compared in multiple nucleotide binding states. This approach will also be used for structural analysis of human beta-cardiac myosin, which will be the first mammalian striated muscle myosin analyzed at atomic resolution.
Our third aim will test our hypotheses about the effects of a mutation in myosin that is known to cause restrictive cardiomyopathy. We will create a Drosophila model of this human disease by mutating the invariant proline at the myosin head-rod junction. We will define the biochemical, biophysical, mechanical and locomotory defects engendered by the myosin mutation. We will also examine whether the mutation affects the flexibility of the myosin head and determine how it influences Drosophila heart (dorsal vessel) structure and function. Overall, our novel integrative analyses will permit testing of models for the transduction of chemical energy into movement and will yield insight into how myosin functions in muscle. Further, we will directly address the role of myosin in human muscle disease, by defining the molecular basis of a restrictive cardiomyopathy.

Public Health Relevance

We study the structural and functional differences among alternative forms of the myosin motor protein in order to elucidate how these isoforms differentially regulate contraction of various muscle types during normal locomotion. We will also examine the role of myosin mutation in muscle disease initiation and progression by developing a genetic model for myosin-based restrictive cardiomyopathy. This is relevant to human health in that mutations in myosin cause heart diseases such as dilated, restrictive and hypertrophic cardiomyopathy, as well as skeletal muscle diseases such as inclusion body myopathy, central core disease, early onset distal myopathy and myosin storage myopathy.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Skeletal Muscle and Exercise Physiology Study Section (SMEP)
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Gindhart, Joseph G
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San Diego State University
Schools of Arts and Sciences
San Diego
United States
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Kronert, William A; Melkani, Girish C; Melkani, Anju et al. (2014) Mapping interactions between myosin relay and converter domains that power muscle function. J Biol Chem 289:12779-90
Caldwell, James T; Melkani, Girish C; Huxford, Tom et al. (2012) Transgenic expression and purification of myosin isoforms using the Drosophila melanogaster indirect flight muscle system. Methods 56:25-32
Kronert, William A; Melkani, Girish C; Melkani, Anju et al. (2012) Alternative relay and converter domains tune native muscle myosin isoform function in Drosophila. J Mol Biol 416:543-57
Kaushik, Gaurav; Zambon, Alexander C; Fuhrmann, Alexander et al. (2012) Measuring passive myocardial stiffness in Drosophila melanogaster to investigate diastolic dysfunction. J Cell Mol Med 16:1656-62
Bloemink, Marieke J; Melkani, Girish C; Dambacher, Corey M et al. (2011) Two Drosophila myosin transducer mutants with distinct cardiomyopathies have divergent ADP and actin affinities. J Biol Chem 286:28435-43
Cammarato, Anthony; Ahrens, Christian H; Alayari, Nakissa N et al. (2011) A mighty small heart: the cardiac proteome of adult Drosophila melanogaster. PLoS One 6:e18497
Cammarato, Anthony; Li, Xiaochuan Edward; Reedy, Mary C et al. (2011) Structural basis for myopathic defects engendered by alterations in the myosin rod. J Mol Biol 414:477-84
Kronert, William A; Melkani, Girish C; Melkani, Anju et al. (2010) Mutating the converter-relay interface of Drosophila myosin perturbs ATPase activity, actin motility, myofibril stability and flight ability. J Mol Biol 398:625-32
Bloemink, Marieke J; Dambacher, Corey M; Knowles, Aileen F et al. (2009) Alternative exon 9-encoded relay domains affect more than one communication pathway in the Drosophila myosin head. J Mol Biol 389:707-21
Kronert, William A; Dambacher, Corey M; Knowles, Aileen F et al. (2008) Alternative relay domains of Drosophila melanogaster myosin differentially affect ATPase activity, in vitro motility, myofibril structure and muscle function. J Mol Biol 379:443-56

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