# Mechanisms of Thin Filament Regulation by Myosin Binding Protein-C

> **NIH NIH R01** · UNIVERSITY OF ARIZONA · 2022 · $559,452

## Abstract

ABSTRACT
 Cardiac myosin binding protein-C (cMyBP-C) is an essential regulator of heart function that is
necessary for normal systolic and diastolic heart function and for enhanced contractility in response to inotropic
agonists that phosphorylate cMyBP-C through numerous signaling pathways. Whereas phosphorylation is
associated with cardiac protection, hypo-phosphorylation is consistently found in heart failure. Mutations in
MYBPC3, the gene encoding cMyBP-C, are also the most common cause of hypertrophic cardiomyopathy
(HCM), a disease with a prevalence of ~1:500. However, despite its significance to cardiac health and disease,
there is still remarkably little known regarding how cMyBP-C mediates its functional effects or how cMyBP-C
phosphorylation increases cardiac contractility in response to inotropic stimuli. Work from our 3 labs has shown
unequivocally that cMyBP-C directly activates the thin filament in muscle sarcomeres in the same way as
myosin cross-bridges. Our data thus demonstrate cMyBP-C effects to augment contraction or delay relaxation
are due to direct effects of cMyBP-C to shift tropomyosin to an activated state on the thin filament. Here we
take advantage of the revolution in cryo-EM to reveal detailed structures of cMyBP-C interactions with the thin
filament and also with myosin-S1 for the first time. We will use cryo-EM reconstructions to identify key residues
that mediate interactions with thin filaments and myosin-S1 and will test model predictions using an arsenal of
functional approaches including a novel (“Spy-C”) method developed exclusively in our labs that allow us to
replace the N'-terminal domains of cMyBP-C in sarcomeres in situ. Using our structural maps, we demonstrate
proof of principle by identifying amino acids responsible for cMyBP-C activation of tropomyosin and show that
phosphorylation causes cMyBP-C domains to reposition on the thin filament. Specific aims will build on these
discoveries and combine our unique resources to: 1) Determine how individual cMyBP-C domains
communicate with neighboring domains when bound to the thin filament and myosin-S1, and 2) Define how
Ca2+ and phosphorylation modulate key regulatory interactions of cMyBP-C with the thin filament and myosin-
S1. By identifying the critical molecular interactions that control cMyBP-C binding to the thin filament and
myosin-S1 these studies will pave the way for future targeted approaches to modulate cardiac contraction and
relaxation.

## Key facts

- **NIH application ID:** 10306335
- **Project number:** 5R01HL140925-04
- **Recipient organization:** UNIVERSITY OF ARIZONA
- **Principal Investigator:** Vitold Galkin
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $559,452
- **Award type:** 5
- **Project period:** 2018-12-17 → 2024-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10306335

## Citation

> US National Institutes of Health, RePORTER application 10306335, Mechanisms of Thin Filament Regulation by Myosin Binding Protein-C (5R01HL140925-04). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10306335. Licensed CC0.

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