Binding of myosin binding protein-C to myosin subfragment S2 affects contractility independent of a tether mechanism.
Mutations in the cardiac myosin binding protein-C gene (cMyBP-C) are among the most prevalent causes of inherited hypertrophic cardiomyopathy. Although most cMyBP-C mutations cause reading frameshifts that are predicted to encode truncated peptides, it is not known if or how expression of these peptides causes disease. One possibility is that because the N-terminus contains a unique binding site for the S2 subfragment of myosin, shortened cMyBP-C peptides could directly affect myosin contraction by binding to S2. To test this hypothesis, we compared the effects of a C1C2 protein containing the myosin S2 binding site on contractile properties in permeabilized myocytes from wild-type and cMyBP-C knockout mice. In wild-type myocytes, the C1C2 protein reversibly increased myofilament Ca2+ sensitivity of tension, but had no effect on resting tension. Identical results were observed in cMyBP-C knockout myocytes where C1C2 increased Ca2+ sensitivity of tension with the half-maximal response elicited at approximately 5 micromol/L C1C2. Maximum force was not affected by C1C2. However, phosphorylation of C1C2 by cAMP-dependent protein kinase reduced its ability to increase Ca2+ sensitivity. These results demonstrate that binding of the C1C2 peptide to S2 alone is sufficient to affect myosin contractile function and suggest that regulated binding of cMyBP-C to myosin S2 by phosphorylation directly influences myofilament Ca2+ sensitivity.
Department of Bioengineering, Box 357962, University of Washington, Seattle, WA 98195, USA. spharris@u.washington.edu
Samantha P
SP
Harris
Elena
E
Rostkova
Mathias
M
Gautel
Richard L
RL
Moss
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology*; D015879:Myosin Subfragments / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D013329:Structure-Activity Relationship; D000099163:Myosin Binding Protein C
D002118:Calcium; D002352:Carrier Proteins; D008840:Microfilament Proteins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D000099163:Myosin Binding Protein C