Quantification of the calcium-induced secondary structural changes in the regulatory domain of troponin-C.
The backbone resonance assignments have been completed for the apo (1H and 15N) and calcium-loaded (1H, 15N, and 13C) regulatory N-domain of chicken skeletal troponin-C (1-90), using multidimensional homonuclear and heteronuclear NMR spectroscopy. The chemical-shift information, along with detailed NOE analysis and 3JHNH alpha coupling constants, permitted the determination and quantification of the Ca(2+)-induced secondary structural change in the N-domain of TnC. For both structures, 5 helices and 2 short beta-strands were found, as was observed in the apo N-domain of the crystal structure of whole TnC (Herzberg O, James MNG, 1988, J Mol Biol 203:761-779). The NMR solution structure of the apo form is indistinguishable from the crystal structure, whereas some structural differences are evident when comparing the 2Ca2+ state solution structure with the apo one. The major conformational change observed is the straightening of helix-B upon Ca2+ binding. The possible importance and role of this conformational change is explored. Previous CD studies on the regulatory domain of TnC showed a significant Ca(2+)-induced increase in negative ellipticity, suggesting a significant increase in helical content upon Ca2+ binding. The present study shows that there is virtually no change in alpha-helical content associated with the transition from apo to the 2Ca2+ state of the N-domain of TnC. Therefore, the Ca(2+)-induced increase in ellipticity observed by CD does not relate to a change in helical content, but more likely to changes in spatial orientation of helices.
Gagné
S M
SM
Department of Biochemistry, University of Alberta, Edmonton, Canada.
Tsuda
S
S
Li
M X
MX
Chandra
M
M
Smillie
L B
LB
Sykes
B D
BD
D000595:Amino Acid Sequence; D000818:Animals; D001059:Apoproteins / Q000737:chemistry; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002645:Chickens; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009119:Muscle Contraction; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D014336:Troponin / Q000737:chemistry* / Q000378:metabolism; D019209:Troponin C
D001059:Apoproteins; D014336:Troponin; D019209:Troponin C; D002118:Calcium