Myosin-binding protein C (MyBP-C) is a thick (myosin) filament component of vertebrate striated muscle that plays a key role in modulating contraction. Three distinct isoforms are encoded by different genes, resulting in the expression of fast and slow skeletal muscle MyBP-C isoforms and a third (cardiac) isoform. Since its discovery in skeletal muscle 40 years ago, most studies of MyBP-C have focused on the cardiac isoform, because mutations in this isoform are a prime cause of inherited cardiomyopathies. However, the recent discovery that mutations in slow skeletal MyBP-C cause skeletal muscle myopathies, one of which is neonatally lethal, makes it clear that defining the molecular structure and function of the skeletal MyBP-C isoforms is critically important. Therefore, in this dual-PI proposal, PIs Craig (UMMS) and Warshaw (UVM), in collaboration with Drs. Irving (Illinois) and Sadayappan (Loyola), will combine their labs' expertise in high resolution imaging and single molecule biophysics coupled with X-ray diffraction, molecular biology and mass spectrometry to elucidate the molecular structure and function of skeletal MyBP-C.
In Aim 1, in situ and in vitro model systems will help determine if MyBP-C activates and/or mechanically modulates the calcium- dependent sliding of native thin (actin) filaments over native thick filaments from fast and slow rat skeletal fibers and whether contractile modulation occurs only where MyBP-C exists in the thick filament.
In Aim 2, through a novel super-resolution light microscopic technique, we will determine whether the MyBP-C N terminus functions by binding to actin and/or myosin. In complementary experiments, fiber X-ray analysis and EM 3D reconstruction of native thin and thick filaments will determine if MyBP-C displaces tropomyosin to activate the thin filament and/or directly influences myosin head interactions to modulate head function.
In Aim 3, the structural and functional consequences of MyBP-C N-terminal domain isoform differences between fast and slow MyBP-C will be characterized with special emphasis on 2 slow MyBP-C splice variants thought to affect actin and myosin binding. Through structural mutagenesis, N-terminal fragments will be expressed with domain deletions and slow MyBP-C splice inserts in an effort to define the domains and inserts that confer MyBP-C's modulation of actomyosin function. Although skeletal MyBP-C's clinical impact is apparent, its functional role is far from certain and thus this dual-PI proposal, tightly integrating MyBP-C structure and function, offers an opportunity to rapidly advance our understanding of both fast and slow skeletal MyBP-C isoforms in their normal state.

Public Health Relevance

The muscles that move our bodies do so through interactions between the thin and thick protein filaments from which muscles are built. Myosin-binding protein C (MyBP-C) is a thick filament component that helps regulate muscle contraction, and genetic defects in MyBP-C are a cause of skeletal muscle diseases. In this project we will use sophisticated microscopy and other techniques to reveal how MyBP-C functions, providing new insights into the molecular mechanisms by which skeletal muscle contraction is regulated.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR067279-03
Application #
9301480
Study Section
Skeletal Muscle and Exercise Physiology Study Section (SMEP)
Program Officer
Boyce, Amanda T
Project Start
2015-08-01
Project End
2020-06-30
Budget Start
2017-07-01
Budget End
2018-06-30
Support Year
3
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of Massachusetts Medical School Worcester
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
603847393
City
Worcester
State
MA
Country
United States
Zip Code
01655
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Lin, Brian Leei; Li, Amy; Mun, Ji Young et al. (2018) Skeletal myosin binding protein-C isoforms regulate thin filament activity in a Ca2+-dependent manner. Sci Rep 8:2604
Lee, Kyoung Hwan; Sulbarán, Guidenn; Yang, Shixin et al. (2018) Interacting-heads motif has been conserved as a mechanism of myosin II inhibition since before the origin of animals. Proc Natl Acad Sci U S A 115:E1991-E2000
Craig, Roger (2017) Molecular structure of muscle filaments determined by electron microscopy. Appl Microsc 47:226-232
Kensler, Robert W; Craig, Roger; Moss, Richard L (2017) Phosphorylation of cardiac myosin binding protein C releases myosin heads from the surface of cardiac thick filaments. Proc Natl Acad Sci U S A 114:E1355-E1364
Mun, Ji Young; Kensler, Robert W; Harris, Samantha P et al. (2016) The cMyBP-C HCM variant L348P enhances thin filament activation through an increased shift in tropomyosin position. J Mol Cell Cardiol 91:141-7
Yang, Shixin; Woodhead, John L; Zhao, Fa-Qing et al. (2016) An approach to improve the resolution of helical filaments with a large axial rise and flexible subunits. J Struct Biol 193:45-54