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Phosphorylation and calcium antagonistically tune myosin-binding protein C's structure and function
Authors
Previs, Michael J.Mun, Ji Young
Michalek, Arthur J.
Previs, Samantha Beck
Gulick, James
Robbins, Jeffrey
Warshaw, David M.
Craig, Roger
UMass Chan Affiliations
Department of Cell and Developmental BiologyDocument Type
Journal ArticlePublication Date
2016-03-22
Metadata
Show full item recordAbstract
During each heartbeat, cardiac contractility results from calcium-activated sliding of actin thin filaments toward the centers of myosin thick filaments to shorten cellular length. Cardiac myosin-binding protein C (cMyBP-C) is a component of the thick filament that appears to tune these mechanochemical interactions by its N-terminal domains transiently interacting with actin and/or the myosin S2 domain, sensitizing thin filaments to calcium and governing maximal sliding velocity. Both functional mechanisms are potentially further tunable by phosphorylation of an intrinsically disordered, extensible region of cMyBP-C's N terminus, the M-domain. Using atomic force spectroscopy, electron microscopy, and mutant protein expression, we demonstrate that phosphorylation reduced the M-domain's extensibility and shifted the conformation of the N-terminal domain from an extended structure to a compact configuration. In combination with motility assay data, these structural effects of M-domain phosphorylation suggest a mechanism for diminishing the functional potency of individual cMyBP-C molecules. Interestingly, we found that calcium levels necessary to maximally activate the thin filament mitigated the structural effects of phosphorylation by increasing M-domain extensibility and shifting the phosphorylated N-terminal fragments back to the extended state, as if unphosphorylated. Functionally, the addition of calcium to the motility assays ablated the impact of phosphorylation on maximal sliding velocities, fully restoring cMyBP-C's inhibitory capacity. We conclude that M-domain phosphorylation may have its greatest effect on tuning cMyBP-C's calcium-sensitization of thin filaments at the low calcium levels between contractions. Importantly, calcium levels at the peak of contraction would allow cMyBP-C to remain a potent contractile modulator, regardless of cMyBP-C's phosphorylation state.Source
Proc Natl Acad Sci U S A. 2016 Mar 22;113(12):3239-44. doi: 10.1073/pnas.1522236113. Epub 2016 Feb 23. Link to article on publisher's site
DOI
10.1073/pnas.1522236113Permanent Link to this Item
http://hdl.handle.net/20.500.14038/26497PubMed ID
26908872Related Resources
Link to Article in PubMedRights
Publisher PDF posted as allowed by the publisher's author rights policy at http://www.pnas.org/site/aboutpnas/authorfaq.xhtml.
ae974a485f413a2113503eed53cd6c53
10.1073/pnas.1522236113