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*H NMR Study on Amide Proton Exchange of Calmodulin-Mastoparan Complex

By Kunio Hikichi


Amide proton exchange rates of Ca2+-saturated calmodulin and Ca2+-saturated calmodulin-mastoparan complex were studied by 'H NMR spectroscopy. Exchange rates of Gly25, Gly61, Gly98, Glyl34, Ile27, IlelOO, and Asnl37 were determined for Ca2+-saturated calmodulin and for Cal+-saturated calmodulin-mastoparan complex, and were found to be less than 10" ' s~'. All these residues of which the amide proton resonances appear at lower fields were considered to form hydrogen bonds, based on the results of X-ray analysis. Exchange rates of Ile27 and Asnl37 became an order of magnitude smaller when mastopar-an bound to Ca2+-saturated calmodulin, while those of the four glycines and IlelOO did not change appreciably. The reduction in accessibility of Asnl37 to water cased by mastoparan binding suggests that a part of the mastoparan binding site is probably located in or near the hydrophobic cluster of the C-terminal-half domain. The reduction in accessibility of Ile27 also suggests that another part of the mastoparan binding site is located in or near the hydrophobic cleft of the N-terminal-half domain. Calmodulin (CaM; Afr = 16,700; 148 amino acids) is known to regulate the activation of several enzymes in a Ca2+

Year: 1990
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