BPS2026 – The C1-M region of cardiac myosin-binding protein-C forms a critical damping module that suppresses sarcomeric oscillations

Cardiac myosin-binding protein-C (cMyBP-C) is essential for regulating cardiac contraction, and its loss is a primary cause of hypertrophic cardiomyopathy (HCM). Our lab’s identified a key function of cMyBP-C is to suppress oscillatory contractions (SPOCs)—an intrinsic myofilament instability that arises at submaximal Ca 2+ activation. However, the domains of cMyBP-C responsible for this damping function remain unknown. To map this function, we used our “cut-and-paste” system in permeabilized cardiomyocytes from gene-edited SpyC3 mice. After enzymatic removal of the endogenous N'-terminal domains (C0–C7), we performed stoichiometric replacement with recombinant constructs containing targeted deletions. We quantified the resulting instability using a novel cross-correlation velocimetry method, which tracks subcellular motion to capture the spectrum of SPOC events. We pool hundreds of individual oscillatory events from multiple preparations to analyze the distribution of SPOC properties, rather than relying on per-preparation averages. Removal of endogenous cMyBP-C unleashed a broad distribution of high-amplitude (0.1–0.4 μm) and low frequency (0.5–2.5 Hz) SPOCs. While reconstitution with the full-length wild-type N’ terminus (WT C0–C7) completely suppressed these oscillations, reconstitution with a construct lacking the M-domain failed to suppress SPOC, yielding a distribution of amplitudes and frequencies nearly identical to the condition without C0–C7. Furthermore, preliminary results with a construct lacking the C1-domain suggest a similar failure to suppress SPOC, indicating its critical role in the damping function. Our results demonstrate that the M-domain is necessary for the primary damping function for the primary damping function of cMyBP-C, with early data suggesting the C1-domain is also essential. Our data suggest that the C1-M region of cMyBP-C constitutes a “minimal damping module” that is required for suppressing sarcomeric oscillations, providing a framework for understanding how HCM-causing mutations in this region lead to myofilament instability.