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Quantification of the calcium‐induced secondary structural changes in the regulatory domain of troponin‐C
Author(s) -
Gagné Stéphane M.,
Tsuda Sakae,
Li Monica X.,
Chandra Murali,
Smillie Lawrence B.,
Sykes Brian D.
Publication year - 1994
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560031108
Subject(s) - heteronuclear molecule , chemistry , conformational change , homonuclear molecule , crystallography , troponin c , calcium , helix (gastropod) , nuclear magnetic resonance spectroscopy , protein secondary structure , crystal structure , biophysics , stereochemistry , molecule , biochemistry , troponin , biology , psychology , ecology , organic chemistry , psychiatry , myocardial infarction , snail
The backbone resonance assignments have been completed for the apo ( 1 H and 15 N) and calcium‐loaded ( 1 H, 15 N, and 13 C) 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 3 J HNHα 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 β‐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 2Ca 2+ state solution structure with the apo one. The major conformational change observed is the straightening of helix‐B upon Ca 2+ 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 Ca 2+ binding. The present study shows that there is virtually no change in α‐helical content associated with the transition from apo to the 2Ca 2+ 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.