1a2x
From Proteopedia
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COMPLEX OF TROPONIN C WITH A 47 RESIDUE (1-47) FRAGMENT OF TROPONIN I
Overview
Troponin (Tn), the complex of three subunits (TnC, TnI, and TnT), plays a, key role in Ca2+-dependent regulation of muscle contraction. To elucidate, the interactions between the Tn subunits and the conformation of TnC in, the Tn complex, we have determined the crystal structure of TnC (two Ca2+, bound state) in complex with the N-terminal fragment of TnI (TnI1-47). The, structure was solved by the single isomorphous replacement method in, combination with multiple wavelength anomalous dispersion data. The, refinement converged to a crystallographic R factor of 22.2% (Rfree =, 32.6%). The central, connecting alpha-helix observed in the structure of, uncomplexed TnC (TnCfree) is unwound at the center (residues Ala-87, Lys-88, Gly-89, Lys-90, and Ser-91) and bent by 90 degrees. As a result, TnC in the complex has a compact globular shape with direct interactions, between the N- and C-terminal lobes, in contrast to the elongated, dumb-bell shaped molecule of uncomplexed TnC. The 31-residue long TnI1-47, alpha-helix stretches on the surface of TnC and stabilizes its compact, conformation by multiple contacts with both TnC lobes. The amphiphilic, C-end of the TnI1-47 alpha-helix is bound in the hydrophobic pocket of the, TnC C-lobe through 38 van der Waals interactions. The results indicate the, major difference between Ca2+ receptors integrated with the other proteins, (TnC in Tn) and isolated in the cytosol (calmodulin). The TnC/TnI1-47, structure implies a mechanism of how Tn regulates the muscle contraction, and suggests a unique alpha-helical regulatory TnI segment, which binds to, the N-lobe of TnC in its Ca2+ bound conformation.
About this Structure
1A2X is a Protein complex structure of sequences from Oryctolagus cuniculus with CA as ligand. Full crystallographic information is available from OCA.
Reference
Crystal structure of troponin C in complex with troponin I fragment at 2.3-A resolution., Vassylyev DG, Takeda S, Wakatsuki S, Maeda K, Maeda Y, Proc Natl Acad Sci U S A. 1998 Apr 28;95(9):4847-52. PMID:9560191
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