PMID: 2504282May 30, 1989Paper

pH-dependent conformational changes of wheat germ calmodulin

Biochemistry
C L Wang

Abstract

Fluorescence energy transfer measurements were carried out between landmarks on wheat germ calmodulin to measure the interdomain distance. Tb3+ ions bound at the four Ca2+-binding sites were used as energy donors, and an organic chromophore, [4-(dimethylamino)-phenyl-4'-azophenyl]maleimide, attached to the single cysteine residue at position 27, was used as the acceptor. At pH's near neutrality all bound Tb3+ ions emit luminescence with shortened lifetimes as a result of energy transfer to the acceptor; at pH 5, however, part of the metal emission becomes unquenched. When the protein is subjected to limited digestion with trypsin in the presence of Ca2+, resulting in the formation of two fragments, each corresponding to half of the molecule, the decay of Tb3+ emission is no longer pH sensitive. These results suggest that, like rabbit skeletal troponin C [Wang, C.-L. A., Zhan, Q., Tao, T., & Gergely, J. (1987) J. Biol. Chem. 257, 8372-8375], wheat germ calmodulin exists in a relatively compact conformation at neutral pH's, but becomes more elongated at pH 5.

References

Jan 1, 1978·Methods in Enzymology·R H Fairclough, C R Cantor
Jan 1, 1978·Annual Review of Biochemistry·L Stryer
Mar 1, 1988·Journal of Biochemistry·O MinowaK Yagi
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Nov 1, 1970·Proceedings of the National Academy of Sciences of the United States of America·S A LattB L Valee
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May 1, 1982·European Journal of Biochemistry·C L WangJ Gergely

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