Myosin-binding protein C N-terminal domains slow Ca2+ dissociation from cardiac thin filaments
- 1Department of Cellular & Molecular Medicine, University of Arizona, Tucson, Arizona, USA
- 2Department of Biomedical Engineering, University of Arizona, Tucson, Arizona, USA
Abstract
The cardiac thin filament (cTF) regulates contraction through Ca2+ binding to, and release from, cardiac troponin C (cTnC), yet how sarcomeric accessory proteins influence these kinetics remains incompletely understood. Cardiac myosin-binding protein C (cMyBP-C) N-terminal domains interact with the thin filament and are regulated by PKA-mediated phosphorylation. To determine whether cMyBP-C alters thin filament Ca2+ exchange kinetics, we performed stopped-flow measurements using 2-(4´-(iodoacetamido)anilino)naphthalene-6-sulfonic acid-labeled cTnC in reconstituted cTFs. The N-terminal fragments C0-C2 and C1-C2 slowed Ca2+ dissociation in a concentration-dependent manner, whereas C0-C1 produced only a modest effect. PKA-mediated phosphorylation markedly attenuated the slowing by C0-C2 and C1-C2. Thus, N-terminal domain composition and phosphorylation state strongly influence cMyBP-C-mediated regulation of thin filament Ca2+ dissociation. In contrast, the tested cMyBP-C fragments did not alter Ca2+ association kinetics or Ca2+ dissociation from isolated troponin. Cosedimentation measurements further showed that differences in kinetic effects were not explained solely by differences in thin filament occupancy. Together, these results demonstrate that cMyBP-C N-terminal fragments selectively modulate Ca2+ dissociation from cTnC in myosin-free reconstituted cTFs. The absence of an effect on isolated troponin is consistent with regulation involving additional thin filament components, including actin and/or tropomyosin, although tropomyosin-dependent and -independent mechanisms remain possible. This work identifies a previously unrecognized effect of cMyBP-C N-terminal domains on cTnC Ca2+ dissociation in the cTF.
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BibTeX
@article{hauck2026myosinbinding,
title = {{Myosin-binding protein C N-terminal domains slow Ca2+ dissociation from cardiac thin filaments}},
author = {Garrett T. Hauck and Fiona L. Wong and Matthew M. Klass and Rhye-Samuel Kanassatega and Victoria C. Lepak and Thomas A. Bunch and Jil C. Tardiff and Brett A. Colson},
journal = {The Journal of Biological Chemistry},
year = {2026},
month = sep,
doi = {10.1016/j.jbc.2026.113601},
url = {https://doi.org/10.1016/j.jbc.2026.113601},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Myosin-binding protein C N-terminal domains slow Ca2+ dissociation from cardiac thin filaments
AU - Garrett T. Hauck
AU - Fiona L. Wong
AU - Matthew M. Klass
AU - Rhye-Samuel Kanassatega
AU - Victoria C. Lepak
AU - Thomas A. Bunch
AU - Jil C. Tardiff
AU - Brett A. Colson
PY - 2026
DA - 2026/09/23
JO - The Journal of Biological Chemistry
DO - 10.1016/j.jbc.2026.113601
UR - https://doi.org/10.1016/j.jbc.2026.113601
AB - The cardiac thin filament (cTF) regulates contraction through Ca2+ binding to, and release from, cardiac troponin C (cTnC), yet how sarcomeric accessory proteins influence these kinetics remains incompletely understood. Cardiac myosin-binding protein C (cMyBP-C) N-terminal domains interact with the thin filament and are regulated by PKA-mediated phosphorylation. To determine whether cMyBP-C alters thin filament Ca2+ exchange kinetics, we performed stopped-flow measurements using 2-(4´-(iodoacetamido)anilino)naphthalene-6-sulfonic acid-labeled cTnC in reconstituted cTFs. The N-terminal fragments C0-C2 and C1-C2 slowed Ca2+ dissociation in a concentration-dependent manner, whereas C0-C1 produced only a modest effect. PKA-mediated phosphorylation markedly attenuated the slowing by C0-C2 and C1-C2. Thus, N-terminal domain composition and phosphorylation state strongly influence cMyBP-C-mediated regulation of thin filament Ca2+ dissociation. In contrast, the tested cMyBP-C fragments did not alter Ca2+ association kinetics or Ca2+ dissociation from isolated troponin. Cosedimentation measurements further showed that differences in kinetic effects were not explained solely by differences in thin filament occupancy. Together, these results demonstrate that cMyBP-C N-terminal fragments selectively modulate Ca2+ dissociation from cTnC in myosin-free reconstituted cTFs. The absence of an effect on isolated troponin is consistent with regulation involving additional thin filament components, including actin and/or tropomyosin, although tropomyosin-dependent and -independent mechanisms remain possible. This work identifies a previously unrecognized effect of cMyBP-C N-terminal domains on cTnC Ca2+ dissociation in the cTF.
SN - 0021-9258
SN - 1083-351X
ER -