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Solution structure and fluctuation of the Mg2+-bound form of calmodulin C-terminal domain

✍ Scribed by Wakana Ohashi; Hiroshi Hirota; Toshio Yamazaki

Publisher
Cold Spring Harbor Laboratory Press
Year
2011
Tongue
English
Weight
744 KB
Volume
20
Category
Article
ISSN
0961-8368

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✦ Synopsis

Abstract

Calmodulin (CaM) is a Ca^2+^‐binding protein that functions as a ubiquitous Ca^2+^‐signaling molecule, through conformational changes from the “closed” apo conformation to the “open” Ca^2+^‐bound conformation. Mg^2+^ also binds to CaM and stabilizes its folded structure, but the NMR signals are broadened by slow conformational fluctuations. Using the E104D/E140D mutant, designed to decrease the signal broadening in the presence of Mg^2+^ with minimal perturbations of the overall structure, the solution structure of the Mg^2+^‐bound form of the CaM C‐terminal domain was determined by multidimensional NMR spectroscopy. The Mg^2+^‐induced conformational change mainly occurred in EF hand IV, while EF‐hand III retained the apo structure. The helix G and helix H sides of the binding sequence undergo conformational changes needed for the Mg^2+^ coordination, and thus the helices tilt slightly. The aromatic rings on helix H move to form a new cluster of aromatic rings in the hydrophobic core. Although helix G tilts slightly to the open orientation, the closed conformation is maintained. The fact that the Mg^2+^‐induced conformational changes in EF‐hand IV and the hydrophobic core are also seen upon Ca^2+^ binding suggests that the Ca^2+^‐induced conformational changes can be divided into two categories, those specific to Ca^2+^ and those common to Ca^2+^ and Mg^2+^.

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