A model structure of the muscle protein complex 4Ca2+.troponin C.troponin I derived from small-angle scattering data: implications for regulation.
We report here a model structure for 4Ca2+.troponin C.troponin I derived from small-angle X-ray and neutron scattering data using a Monte Carlo modeling method. In this model, troponin I appears as a spiral structure that wraps around 4Ca2+.troponin C which adopts an extended dumbbell conformation similar to that observed in the crystal structures of troponin C. The troponin I spiral has the approximate dimensions of an alpha-helix and winds through the hydrophobic "cups" in each globular domain of troponin C. The model is consistent with a body of previously published biochemical data on the interactions between troponin C and troponin I, and suggests the molecular mechanism for the Ca(2+)-sensitive switch that regulates the muscle contraction/relaxation cycle involves a signal transmitted via the central spiral region of troponin I.
Olah
G A
GA
Chemical Science and Technology Division, Los Alamos National Laboratory, New Mexico 87545.
Trewhella
J
J
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009010:Monte Carlo Method; D009502:Neutrons; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012542:Scattering, Radiation; D014336:Troponin / Q000737:chemistry* / Q000378:metabolism*; D019209:Troponin C; D019210:Troponin I; D014965:X-Rays
D014336:Troponin; D019209:Troponin C; D019210:Troponin I; D002118:Calcium