title: The myosin-binding protein C motif binds to F-actin in a phosphorylation-sensitive manner.
abstract: Cardiac myosin-binding protein C (cMyBP-C) is a regulatory protein expressed in cardiac sarcomeres that is known to interact with myosin, titin, and actin. cMyBP-C modulates actomyosin interactions in a phosphorylation-dependent way, but it is unclear whether interactions with myosin, titin, or actin are required for these effects. Here we show using cosedimentation binding assays, that the 4 N-terminal domains of murine cMyBP-C (i.e. C0-C1-m-C2) bind to F-actin with a dissociation constant (K(d)) of approximately 10 microm and a molar binding ratio (B(max)) near 1.0, indicating 1:1 (mol/mol) binding to actin. Electron microscopy and light scattering analyses show that these domains cross-link F-actin filaments, implying multiple sites of interaction with actin. Phosphorylation of the MyBP-C regulatory motif, or m-domain, reduced binding to actin (reduced B(max)) and eliminated actin cross-linking. These results suggest that the N terminus of cMyBP-C interacts with F-actin through multiple distinct binding sites and that binding at one or more sites is reduced by phosphorylation. Reversible interactions with actin could contribute to effects of cMyBP-C to increase cross-bridge cycling.
authors.affiliation: Department of Neurobiology, Physiology, and Behavior, University of California, Davis, California 95616, USA.
authors.forename: Justin F
authors.initials: JF
authors.lastname: Shaffer
authors.forename: Robert W
authors.initials: RW
authors.lastname: Kensler
authors.forename: Samantha P
authors.initials: SP
authors.lastname: Harris
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D051379:Mice; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D011817:Rabbits; D012518:Sarcomeres / Q000235:genetics / Q000378:metabolism*; D000099163:Myosin Binding Protein C
chemical_list: D000199:Actins; D002352:Carrier Proteins; D000099163:Myosin Binding Protein C