Solution structures of the C-terminal domain of cardiac troponin C free and bound to the N-terminal domain of cardiac troponin I.
The N-terminal domain of cardiac troponin I (cTnI) comprising residues 33-80 and lacking the cardiac-specific amino terminus forms a stable binary complex with the C-terminal domain of cardiac troponin C (cTnC) comprising residues 81-161. We have utilized heteronuclear multidimensional NMR to assign the backbone and side-chain resonances of Ca2+-saturated cTnC(81-161) both free and bound to cTnI(33-80). No significant differences were observed between secondary structural elements determined for free and cTnI(33-80)-bound cTnC(81-161). We have determined solution structures of Ca2+-saturated cTnC(81-161) free and bound to cTnI(33-80). While the tertiary structure of cTnC(81-161) is qualitatively similar to that observed free in solution, the binding of cTnI(33-80) results mainly in an opening of the structure and movement of the loop region between helices F and G. Together, these movements provide the binding site for the N-terminal domain of cTnI. The putative binding site for cTnI(33-80) was determined by mapping amide proton and nitrogen chemical shift changes, induced by the binding of cTnI(33-80), onto the C-terminal cTnC structure. The binding interface for cTnI(33-80), as suggested from chemical shift changes, involves predominantly hydrophobic interactions located in the expanded hydrophobic pocket. The largest chemical shift changes were observed in the loop region connecting helices F and G. Inspection of available TnC sequences reveals that these residues are highly conserved, suggesting a common binding motif for the Ca2+/Mg2+-dependent interaction site in the TnC/TnI complex.
Gasmi-Seabrook
G M
GM
Department of Molecular Genetics, University of Cincinnati, College of Medicine, Ohio 45267, USA.
Howarth
J W
JW
Finley
N
N
Abusamhadneh
E
E
Gaponenko
V
V
Brito
R M
RM
Solaro
R J
RJ
Rosevear
P R
PR
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012996:Solutions; D019209:Troponin C / Q000737:chemistry* / Q000378:metabolism; D019210:Troponin I / Q000737:chemistry* / Q000378:metabolism
D046911:Macromolecular Substances; D010446:Peptide Fragments; D011994:Recombinant Proteins; D012996:Solutions; D019209:Troponin C; D019210:Troponin I