Abstract 16613: Functional Role of Fast Myosin Binding Protein-c Expressed in the Failing Myocardium
Background: Our previous studies showed that fast-skeletal myosin binding protein-C (fMyBP-C) was expressed in the heart during heart failure. cMyBP-C modulates thin filament calcium-sensitivity and cellular contractile velocities, but the exact functional role of fMyBP-C in the heart is unknown. Myosin binding protein-C (MyBP-C) is a sarcomeric thick filament protein in striated muscles, with three isoforms: fMyBP-C, slow-skeletal (sMyBP-C) and cardiac (cMyBP-C). The cardiac isoform differs from the skeletal isoforms by having an extra Ig domain at the N-terminus (C0) and four phosphorylation sites within the MyBP-C motif region.
Hypothesis: Structural differences in the N-terminal regions of the MyBP-C isoforms confer isoform-specific modulation of contractility at both the molecular and cellular levels.
Results: To answer this question, we expressed recombinant proteins encoding N-terminal regions up to and including the C2 domain of sMyBP-C, fMyBP-C and cMyBP-C, and were characterized by in vitro actin-binding, motility, and force-pCa assays. Electron microscopy demonstrated clear binding of N-terminal fragments to F-actin. 3D reconstructions showed slow and cardiac N-terminal fragments resulted in greater tropomyosin movement from the blocked to the closed position relative to fast. In vitro motility assays showed that all three N-terminal fragments were capable of activating native thin filaments at low Ca2+ levels (pCa 7) in a graded manner, but the slow N-terminal fragment was significantly less inhibitory than cardiac and fast N-terminal fragments when fully activated (pCa 5). Force-pCa assays also demonstrated differential regulation by each N-terminal fragment. Finally, adult rat ventricular myocytes overexpressing full-length MyBP-C isoforms were used to assess contraction and relaxation speeds. Sarcomere length shortening studies demonstrated faster relaxation kinetics in sMyBP-C and fMyBP-C when compared to uninfected and cMyBP-C overexpression controls, suggesting a role for the cardiac-specific C0 domain in regulating relaxation.
Conclusion: Together, our data demonstrate that differences in the N-terminal structure of MyBP-C isoforms alter regulation of sarcomere functional properties.
Author Disclosures: B. Lin: None. A. Li: None. J. Mun: None. M. Previs: None. S. Previs: None. C. dos Remedios: None. R. Craig: None. D. Warshaw: None. S. Sadayappan: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.