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

• Published in: Protein science Vol. 20; no. 4; pp. 690 - 701
• Main Authors: Ohashi, Wakana, Hirota, Hiroshi, Yamazaki, Toshio
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.04.2011; Wiley Subscription Services, Inc
• Subjects: calmodulin; conformational exchange; magnesium; NMR; Nuclear magnetic resonance; Protein folding; solution structure
• ISSN: 0961-8368; 1469-896X
• DOI: 10.1002/pro.598

Calmodulin (CaM) is a Ca2+‐binding protein that functions as a ubiquitous Ca2+‐signaling molecule, through conformational changes from the “closed” apo conformation to the “open” Ca2+‐bound conformation. Mg2+ 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 Mg2+ with minimal perturbations of the overall structure, the solution structure of the Mg2+‐bound form of the CaM C‐terminal domain was determined by multidimensional NMR spectroscopy. The Mg2+‐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 Mg2+ 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 Mg2+‐induced conformational changes in EF‐hand IV and the hydrophobic core are also seen upon Ca2+ binding suggests that the Ca2+‐induced conformational changes can be divided into two categories, those specific to Ca2+ and those common to Ca2+ and Mg2+. PDB Code(s): 2EQC