Small-Angle X-ray Scattering Reveals the N-Terminal Domain Organization of Cardiac Myosin Binding Protein C

Cy M. Jeffries, Andrew E. Whitten, Samantha P. Harris, Jill Trewhella

Research output: Contribution to journalArticlepeer-review

57 Scopus citations

Abstract

Myosin binding protein C (MyBP-C) is a multidomain accessory protein of striated muscle sarcomeres. Three domains at the N-terminus of MyBP-C (C1-m-C2) play a crucial role in maintaining and modulating actomyosin interactions. The cardiac isoform has an additional N-terminal domain (C0) that is postulated to provide a greater level of regulatory control in cardiac muscle. We have used small-angle X-ray scattering, ab initio shape restoration, and rigid-body modeling to determine the average shape and spatial arrangement of the four N-terminal domains of cardiac MyBP-C (C0C2) and a three-domain variant that is analogous to the N-terminus of the skeletal isoform (C1C2). We found that the domains of both proteins are tandemly arranged in a highly extended configuration that is sufficiently long to span the interfilament cross-bridge distances in vivo and, hence, be poised to modulate these interactions. The average spatial organization of the C1, m, and C2 domains is not significantly perturbed by the removal of the cardiac-specific C0 domain, suggesting that the interdomain interfaces, while relatively small in area, have a degree of rigidity. Modeling the C0C2 and C1C2 scattering data reveals that the structures of the C0 and m domains (also referred to as the 'MyBP motif') are compact and have dimensions that are consistent with the immunoglobulin fold superfamily of proteins. Sequence analysis, homology modeling, and circular dichroism experiments support the conclusion that the previously undetermined structures of these domains can be characterized as having an immunoglobulin-like fold. Atomic models using the known NMR structures for C1 and C2 as well as homology models for the C0 and m domains provide insights into the placement of conserved serine residues of the m domain that are phosphorylated in vivo and cause a change in muscle fiber contraction by abolishing interactions with myosin.

Original languageEnglish (US)
Pages (from-to)1186-1199
Number of pages14
JournalJournal of Molecular Biology
Volume377
Issue number4
DOIs
StatePublished - Apr 4 2008

Keywords

  • cardiac myosin binding protein C
  • cardiomyopathy
  • immunoglobulin
  • small-angle X-ray scattering
  • titin

ASJC Scopus subject areas

  • Virology

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