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The conformation of calmodulin: A substantial environmentally sensitive helical transition in Ca 4 ‐calmodulin with potential mechanistic function
Author(s) -
Bayley Peter,
Martin Stephen,
Jones Gareth
Publication year - 1988
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(88)80225-4
Subject(s) - calmodulin , chemistry , circular dichroism , crystallography , helix (gastropod) , molecule , crystal structure , stereochemistry , calcium , biology , organic chemistry , ecology , snail
The conformation of Ca 4 ‐calmodulin in solution, as assessed by far‐UV peptide circular dichroism, contains significantly less α‐helix than the proposed X‐ray crystal structure. We now show that Ca 4 ‐calmodulin adopts significant additional helical structure in solution in the presence of a helicogenic solvent (50%, v/v, aqueous 2,2,2‐trifluoroethanol or 50%, v/v, methylpentane‐5,5‐diol). We suggest that the long continuous helix (residues 66–92 of the crystal structure)is not necessarily a normal feature of the calmodulin structure in solution, and may be due in part to the conditions of crystallisation. This result is supported by time‐resolved tyrosine fluorescence anisotropy studies indicating that Ca 4 ‐calmodulin in solution is an essentially compact globular structure which undergoes isotropic rotational motion. We conclude that, under appropriate ionic and apolar environmental conditions, Ca 4 ‐calmodulin undergoes a substantial helical transition, which may involve residues in the central region of the molecule. Such a transition could have an important function in determining specificity and affinity in interactions of calmodulin with different target sequences of Ca 2+ ‐dependent regulatory enzymes.