Orientation of myosin binding protein C in the cardiac muscle sarcomere determined by domain-specific immuno-EM

Kyounghwan Lee, Samantha P. Harris, Sakthivel Sadayappan, Roger Craig

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

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, 43 nm 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.

Original languageEnglish (US)
Pages (from-to)274-286
Number of pages13
JournalJournal of Molecular Biology
Volume427
Issue number2
DOIs
StatePublished - Jan 30 2015

Keywords

  • Cardiac muscle contraction
  • Cardiac muscle disease
  • Cardiac muscle regulation
  • Cardiac muscle structure
  • cMyBP-C

ASJC Scopus subject areas

  • Molecular Biology

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