Fig. 3: Myosin ON/OFF structural parameters of skeletal muscle fibers before (blue) and after (red) cleavage of the fMyBP-C bridge region across SLs.
a M2 cluster before and after fMyBP-C cleavage. b Intensity of the M2 cluster (IM2) cluster. c I1,1/I1,0 provides a measure of the mass distribution between the thick and thin filaments. d M3 spacing (SM3) measures the axial spacing of myosin heads. e M6 spacing (SM6) is the spacing of the thick filament backbone and is often used as a measure of thick filament length. f Representation of myosin OFF–ON transition before (top) after (bottom) N-terminal fMyBP-C cleavage. We predict that a loss of regulation of N-terminal MyBP-C leads to an OFF→ON transition on Cr1 (purple) myosins and has a cooperative effect on surrounding Cr2 and Cr3 myosins to also transition OFF → ON. g Based on mechanical and structural details from the current and other studies, we present a flow chart of myosin head ON/OFF control. This chart shows how myosin heads transition OFF → ON, but we assume the reverse effects will also transition ON → OFF. Statistics throughout are ANOVA designs with main effects treatment, SL, and their interaction, and a random effect of individual, followed by Tukey’s honestly significant difference (HSD) post-hoc test on statistically significant main effects (P < 0.05), and reported in figures as connecting letters: different letters are significantly different. Data throughout was reported as mean ± SE. Experimental dataset derived from 41 fiber bundles from psoas muscles of 15 SNOOPC2 mice (9 male/6 female). Further statistical details are in Supplementary Table 10.
