Ca(2+)-induced conformational shift of the COOH-domain of eel skeletal muscle troponin C in the presence of physiological concentrations of Mg2+.
The spectroscopic properties of Trp152 of eel skeletal muscle troponin C have been studied under conditions in which the COOH-domain is depleted of metal ions, titrated with Mg2+ and subsequently with Ca2+. This spectroscopic study clearly shows that the Mg2+ or Ca(2+)-bound states substitution lead to distinct conformations of the COOH-domain. The analysis of eel troponin C absorption and Trp152 fluorescence emission spectra indicates a more polar environment in the Mg(2+)-bound state of the protein. Steady state tryptophan polarization and lifetime distribution data indicate that the motion of the indole moiety is more restricted in the Mg2+ state of the protein than in the Ca(2+)-bound state. However, fluorescence quenching data using I- and Cs+ show that Trp152 is more accessible to the solvent in the Mg(2+)-bound state of eel troponin C. This spectroscopic analysis of the distinct Ca2+ and Mg(2+)-bound states of eel troponin C is consistent with the description of the three-dimensional structure of the corresponding states of pike (pI = 4.10) parvalbumin which is structurally homologous to the COOH-domain of troponin C. Since it appears that during muscular contraction, magnesium ions, which occupy the binding sites of the COOH-domain of troponin C in the resting cell are replaced by calcium ions, the structural shift occurring upon Mg2+/Ca2+ substitution, must have a physiological significance. The role of this domain is probably not limited to a structural role.
François
J M
JM
Laboratoire de Biochimie, Université de Liège, Belgium.
Sedarous
S S
SS
Gerday
C
C
D020106:Acrylamide; D000178:Acrylamides / Q000494:pharmacology; D000811:Anguilla; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002586:Cesium / Q000494:pharmacology; D005454:Fluorescence Polarization; D007455:Iodine / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000187:drug effects; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D010100:Oxygen / Q000494:pharmacology; D013053:Spectrophotometry; D013329:Structure-Activity Relationship; D019209:Troponin C / Q000737:chemistry* / Q000187:drug effects
D000178:Acrylamides; D019209:Troponin C; D002586:Cesium; D020106:Acrylamide; D009536:Niacinamide; D007455:Iodine; D008274:Magnesium; D010100:Oxygen; D002118:Calcium; C008472:N-methylnicotinamide