Title

The cMyBP-C HCM variant L348P enhances thin filament activation through an increased shift in tropomyosin position

UMMS Affiliation

Department of Cell and Developmental Biology

Date

2-1-2016

Document Type

Article

Abstract

Mutations in cardiac myosin binding protein C (cMyBP-C), a thick filament protein that modulates contraction of the heart, are a leading cause of hypertrophic cardiomyopathy (HCM). Electron microscopy and 3D reconstruction of thin filaments decorated with cMyBP-C N-terminal fragments suggest that one mechanism of this modulation involves the interaction of cMyBP-C's N-terminal domains with thin filaments to enhance their Ca(2+)-sensitivity by displacement of tropomyosin from its blocked (low Ca(2+)) to its closed (high Ca(2+)) position. The extent of this tropomyosin shift is reduced when cMyBP-C N-terminal domains are phosphorylated. In the current study, we have examined L348P, a sequence variant of cMyBP-C first identified in a screen of patients with HCM. In L348P, leucine 348 is replaced by proline in cMyBP-C's regulatory M-domain, resulting in an increase in cMyBP-C's ability to enhance thin filament Ca(2+)-sensitization. Our goal here was to determine the structural basis for this enhancement by carrying out 3D reconstruction of thin filaments decorated with L348P-mutant cMyBP-C. When thin filaments were decorated with wild type N-terminal domains at low Ca(2+), tropomyosin moved from the blocked to the closed position, as found previously. In contrast, the L348P mutant caused a significantly larger tropomyosin shift, to approximately the open position, consistent with its enhancement of Ca(2+)-sensitization. Phosphorylated wild type fragments showed a smaller shift than unphosphorylated fragments, whereas the shift induced by the L348P mutant was not affected by phosphorylation. We conclude that the L348P mutation causes a gain of function by enhancing tropomyosin displacement on the thin filament in a phosphorylation-independent way.

Rights and Permissions

Citation: J Mol Cell Cardiol. 2016 Feb;91:141-7. doi: 10.1016/j.yjmcc.2015.12.014. Epub 2015 Dec 21. Link to article on publisher's site

Related Resources

Link to Article in PubMed

Keywords

Cardiac muscle, Electron microscopy, Hypertrophic cardiomyopathy, Myosin binding protein C, Thin filament, cMyBP-C

Journal Title

Journal of molecular and cellular cardiology

PubMed ID

26718724