title: Structural evidence for the interaction of C-protein (MyBP-C) with actin and sequence identification of a possible actin-binding domain.
abstract: C-protein (MyBP-C) is a myosin-binding protein that is usually seen in two sets of seven to nine positions in the C-zones in each half of the vertebrate striated muscle A-band. Skeletal muscle C-protein is a modular structure containing ten sub-domains (C1 to C10) of which seven are immunoglobulin-type domains and three (C6, C7 and C9) are fibronectin-like domains. Cardiac muscle C-protein has an extra N-terminal domain (C0) and also some sequence insertions, one of which provides phosphorylation sites. It is conceivable that C-protein has both a structural and regulatory role within the sarcomere. The precise mode of binding of C-protein to the myosin filament has not been determined. However, detailed ultrastructural studies have suggested that C-protein, which binds to myosin, can give rise to a longer periodicity (about 435A) than the intrinsic myosin filament repeat of 429A. The reason for this has remained a puzzle for over 25 years. Here we show by modelling and computation that the presence of this longer periodicity could be explained if the myosin-binding part of C-protein binds to myosin with the expected 429A repeat, but if there are systematic interactions of the N-terminal end of C-protein with the neighbouring actin filaments in the hexagonal lattice of filaments in the A-band. We also show that if they occur these interactions would probably only arise in defined muscle states. Further analysis of the MyBP-C sequence identifies a possible actin-binding domain in the Pro-Ala-rich sequence found at the N terminus of skeletal MyBP-C and between domains C0 and C1 in the cardiac sequence.
authors.affiliation: Biological Structure and Function Section, Biomedical Sciences Division, Imperial College London, Fleming Building, London SW7 2AZ, UK. j.squire@imperial.ac.uk
authors.forename: John M
authors.initials: JM
authors.lastname: Squire
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Luther
authors.forename: Carlo
authors.initials: C
authors.lastname: Knupp
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D003198:Computer Simulation; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000737:chemistry / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism; D009218:Myosins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012518:Sarcomeres / Q000737:chemistry / Q000378:metabolism; D012984:Software; D014961:X-Ray Diffraction; D000099163:Myosin Binding Protein C
chemical_list: D000199:Actins; D002352:Carrier Proteins; D009218:Myosins; D000099163:Myosin Binding Protein C