title: Structural insight into unique cardiac myosin-binding protein-C motif: a partially folded domain.
abstract: The structural role of the unique myosin-binding motif (m-domain) of cardiac myosin-binding protein-C remains unclear. Functionally, the m-domain is thought to directly interact with myosin, whereas phosphorylation of the m-domain has been shown to modulate interactions between myosin and actin. Here we utilized NMR to analyze the structure and dynamics of the m-domain in solution. Our studies reveal that the m-domain is composed of two subdomains, a largely disordered N-terminal portion containing three known phosphorylation sites and a more ordered and folded C-terminal portion. Chemical shift analyses, d(NN)(i, i + 1) NOEs, and (15)N{(1)H} heteronuclear NOE values show that the C-terminal subdomain (residues 315-351) is structured with three well defined helices spanning residues 317-322, 327-335, and 341-348. The tertiary structure was calculated with CS-Rosetta using complete (13)C(α), (13)C(β), (13)C', (15)N, (1)H(α), and (1)H(N) chemical shifts. An ensemble of 20 acceptable structures was selected to represent the C-terminal subdomain that exhibits a novel three-helix bundle fold. The solvent-exposed face of the third helix was found to contain the basic actin-binding motif LK(R/K)XK. In contrast, (15)N{(1)H} heteronuclear NOE values for the N-terminal subdomain are consistent with a more conformationally flexible region. Secondary structure propensity scores indicate two transient helices spanning residues 265-268 and 293-295. The presence of both transient helices is supported by weak sequential d(NN)(i, i + 1) NOEs. Thus, the m-domain consists of an N-terminal subdomain that is flexible and largely disordered and a C-terminal subdomain having a three-helix bundle fold, potentially providing an actin-binding platform.
authors.affiliation: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA.
authors.forename: Jack W
authors.initials: JW
authors.lastname: Howarth
authors.forename: Srinivas
authors.initials: S
authors.lastname: Ramisetti
authors.forename: Kristof
authors.initials: K
authors.lastname: Nolan
authors.forename: Sakthivel
authors.initials: S
authors.lastname: Sadayappan
authors.forename: Paul R
authors.initials: PR
authors.lastname: Rosevear
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation / Q000502:physiology; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D000099163:Myosin Binding Protein C
chemical_list: D002352:Carrier Proteins; D000099163:Myosin Binding Protein C