1H NMR study of rabbit skeletal muscle troponin C: Mg2(+)-induced conformational change.
Binding of Mg2+ to rabbit skeletal muscle troponin C (TnC) is studied by means of two-dimensional (2D) 1H NMR spectroscopy. Using the sequence-specific resonance assignment method we assign several resonances of TnC in the Mg2(+)-saturated state. Assigned resonances are used as probes of the following titration experiments: (1) Mg2+ titration of apo-TnC, (2) Mg2+ titration of Ca2TnC, and (3) Mg2+ titration of Ca4TnC. In experiment 1, the slow-exchange behavior is observed for resonances of Phe99, Asp107, Gly108, Tyr109, Ile110, Asp111, His125, Gly144, Arg145, Ile146, Asp147, and Phe148 located at the high-affinity Ca2(+)-binding sites in the C-terminal-half domain. In experiments 1 and 2, the fast-exchange behavior is observed for resonances of Gly32, Asp33, Ser35, Gly68, Thr69, and Asp71 located at the low-affinity Ca2(+)-binding sites in the N-terminal-half domain. These results suggest that Mg2+ ions bind to the N domain as well as the C domain. In experiment 3, no spectral change is observed for all above-mentioned residues in the C domain and also for Gly32 and Gly68 in the N domain. It can be concluded that all Ca2(+)-binding sites in both the N and C domains can bind Mg2+ ions. No significant change is observed for resonances of Phe23, Ile34, Val68, and Phe72 in experiments 1 and 2. These results suggest that Mg2+ binding to the N domain does not induce conformational change in the hydrophobic region of the N domain. 2D-NMR spectra and Mg2(+)-titration data suggest that the antiparallel beta-sheet conformation is formed in both the N and C domains when Mg2+ ions bind to the two domains.
Tsuda
S
S
Department of Polymer Science, Faculty of Science, Hokkaido University, Sapporo, Japan.
Ogura
K
K
Hasegawa
Y
Y
Yagi
K
K
Hikichi
K
K
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009132:Muscles / Q000378:metabolism; D011487:Protein Conformation / Q000187:drug effects; D011817:Rabbits; D014336:Troponin / Q000378:metabolism; D019209:Troponin C
D014336:Troponin; D019209:Troponin C; D008274:Magnesium; D002118:Calcium