Orientation of myosin binding protein C in the cardiac muscle sarcomere determined by domain-specific immuno-EM
Department of Cell and Developmental Biology
Animals; Carrier Proteins; Image Processing, Computer-Assisted; Mice; Microscopy, Fluorescence; Microscopy, Immunoelectron; Myocardial Contraction; Myocardium; Protein Isoforms; Sarcomeres
Myosin binding protein C is a thick filament protein of vertebrate striated muscle. The cardiac isoform [cardiac myosin binding protein C (cMyBP-C)] is essential for normal cardiac function, and mutations in cMyBP-C cause cardiac muscle disease. The rod-shaped molecule is composed primarily of 11 immunoglobulin- or fibronectin-like domains and is located at nine sites, 43nm apart, in each half of the A-band. To understand how cMyBP-C functions, it is important to know its structural organization in the sarcomere, as this will affect its ability to interact with other sarcomeric proteins. Several models, in which cMyBP-C wraps around, extends radially from, or runs axially along the thick filament, have been proposed. Our goal was to define cMyBP-C orientation by determining the relative axial positions of different cMyBP-C domains. Immuno-electron microscopy was performed using mouse cardiac myofibrils labeled with antibodies specific to the N- and C-terminal domains and to the middle of cMyBP-C. Antibodies to all regions of the molecule, except the C-terminus, labeled at the same nine axial positions in each half A-band, consistent with a circumferential and/or radial rather than an axial orientation of the bulk of the molecule. The C-terminal antibody stripes were slightly displaced axially, demonstrating an axial orientation of the C-terminal three domains, with the C-terminus closer to the M-line. These results, combined with previous studies, suggest that the C-terminal domains of cMyBP-C run along the thick filament surface, while the N-terminus extends toward neighboring thin filaments. This organization provides a structural framework for understanding cMyBP-C's modulation of cardiac muscle contraction.
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Citation: J Mol Biol. 2015 Jan 30;427(2):274-86. doi: 10.1016/j.jmb.2014.10.023. Link to article on publisher's site.
cMyBP-C, cardiac muscle contraction, cardiac muscle disease, cardiac muscle regulation, cardiac muscle structure
Journal of molecular biology
Lee, Kyounghwan; Harris, Samantha P.; Sadayappan, Sakthivel; and Craig, Roger, "Orientation of myosin binding protein C in the cardiac muscle sarcomere determined by domain-specific immuno-EM" (2015). Cell and Developmental Biology Publications. 139.