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


Authors: Lee, K; Harris, S. P.; Sadayappan, S; Craig, R.
Article Title: Orientation of myosin binding protein C in the cardiac muscle sarcomere determined by domain-specific immuno-EM
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, 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.
Keywords: Animals; Mice; Image Processing, Computer-Assisted; cMyBP-C; Myocardial Contraction/physiology; Microscopy, Fluorescence; cardiac muscle contraction; cardiac muscle disease; cardiac muscle regulation; cardiac muscle structure; Carrier Proteins/chemistry; Microscopy, Immunoelectron; Myocardium/chemistry; Protein Isoforms/chemistry; Sarcomeres/chemistry
Journal Title: Journal of Molecular Biology
Volume: 427
Issue: 2
ISSN: 1089-8638; 0022-2836
Publisher: Elsevier Inc  
Journal Place: England
Date Published: 2015
Start Page: 274
End Page: 286
Language: eng
DOI/URL:
Notes: LR: 20150401; CI: Copyright (c) 2014; GR: K02 HL114749/HL/NHLBI NIH HHS/United States; GR: K02 HL114749/HL/NHLBI NIH HHS/United States; GR: P01 HL059408/HL/NHLBI NIH HHS/United States; GR: P01 HL059408/HL/NHLBI NIH HHS/United States; GR: R01 AR034711/AR/NIAMS NIH HHS/United States; GR: R01 AR034711/AR/NIAMS NIH HHS/United States; GR: R01 HL080367/HL/NHLBI NIH HHS/United States; GR: R01 HL080367/HL/NHLBI NIH HHS/United States; GR: R01 HL105826/HL/NHLBI NIH HHS/United States; GR: R01 HL105826/HL/NHLBI NIH HHS/United States; GR: S10 RR027897/RR/NCRR NIH HHS/United States; GR: S10 RR027897/RR/NCRR NIH HHS/United States; JID: 2985088R; 0 (Carrier Proteins); 0 (Protein Isoforms); 0 (myosin-binding protein C); CIN: J Mol Biol. 2015 Jan 30;427(2):231-5. PMID: 25463435; NIHMS644559; OID: NLM: NIHMS644559 [Available on 01/30/16]; OID: NLM: PMC4297556 [Available on 01/30/16]; OTO: NOTNLM; PMCR: 2016/01/30 00:00; 2014/08/12 [received]; 2014/10/07 [revised]; 2014/10/08 [accepted]; 2014/11/06 [aheadofprint]; ppublish