Radial displacement of myosin cross-bridges in mouse myocardium due to ablation of myosin binding protein-C.
Myosin binding protein-C (cMyBP-C) is a thick filament accessory protein, which in cardiac muscle functions to regulate the kinetics of cross-bridge interaction with actin; however, the underlying mechanism is not yet understood. To explore the structural basis for cMyBP-C function, we used synchrotron low-angle X-ray diffraction to measure interfilament lattice spacing and the equatorial intensity ratio, I(11)/I(10), in skinned myocardial preparations isolated from wild-type (WT) and cMyBP-C null (cMyBP-C(-/-)). In relaxed myocardium, ablation of cMyBP-C appeared to result in radial displacement of cross-bridges away from the thick filaments, as there was a significant increase ( approximately 30%) in the I(11)/I(10) ratio for cMyBP-C(-/-) (0.37+/-0.03) myocardium as compared to WT (0.28+/-0.01). While lattice spacing tended to be greater in cMyBP-C(-/-) myocardium (44.18+/-0.68 nm) when compared to WT (42.95+/-0.43 nm), the difference was not statistically significant. Furthermore, liquid-like disorder in the myofilament lattice was significantly greater ( approximately 40% greater) in cMyBP-C(-/-) myocardium as compared to WT. These results are consistent with our working hypothesis that cMyBP-C normally acts to tether myosin cross-bridges nearer to the thick filament backbone, thereby reducing the likelihood of cross-bridge binding to actin and limiting cooperative activation of the thin filament.
Colson
Brett A
BA
Department of Physiology, University of Wisconsin Medical School, Madison, WI 53711, USA. bacolson@wisc.edu
Bekyarova
Tanya
T
Fitzsimons
Daniel P
DP
Irving
Thomas C
TC
Moss
Richard L
RL
D008841:Actin Cytoskeleton; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry*; D017115:Catheter Ablation; D004220:Disulfides / Q000737:chemistry; D005260:Female; D008297:Male; D051379:Mice; D009206:Myocardium / Q000737:chemistry*; D009218:Myosins / Q000737:chemistry*; D011487:Protein Conformation; D014961:X-Ray Diffraction; D000099163:Myosin Binding Protein C
D002352:Carrier Proteins; D004220:Disulfides; D009218:Myosins; D000099163:Myosin Binding Protein C