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 Ca2+-sensitivity by displacement of tropomyosin from its blocked (low Ca2+) to its closed (high Ca2+) 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 Ca2+-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 Ca2+, 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 Ca2+-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.
Original language | English (US) |
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Pages (from-to) | 141-147 |
Number of pages | 7 |
Journal | Journal of Molecular and Cellular Cardiology |
Volume | 91 |
DOIs | |
State | Published - Feb 1 2016 |
Externally published | Yes |
Keywords
- Cardiac muscle
- CMyBP-C
- Electron microscopy
- Hypertrophic cardiomyopathy
- Myosin binding protein C
- Thin filament
ASJC Scopus subject areas
- Molecular Biology
- Cardiology and Cardiovascular Medicine