Histidine-49 is necessary for the pH-dependent transition between active and inactive states of the bovine F₁-ATPase inhibitor protein

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• 作者：Schnizer ; Richard ; Van Heeke ; Gino ; Amaturo ; Domenico ; Schuster ; Sheldon M.
• 关键词：ATPase ; F₁- ; Inhibitor protein ; Histidine ; Transition ; pH dependence ; (Bovine)
• 刊名：Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular Enzymology
• 出版年：1996
• 出版时间：February 8, 1996
• 年：1996
• 卷：1292
• 期：2
• 页码：241-248
• 全文大小：1.16 M

文摘

The role of the histidyl residue at position 49 (H49) of the bovine mitochondrial F₁-ATPase inhibitor protein (F₁I) was examined by site-directed mutagenesis. Six amino acids (Q, E, K, V, L, and I) were substituted for H49 and the activities of the resulting inhibitor proteins were characterized with respect to pH. Each of the six mutations abolished the pH sensitivity which is characteristic of wild-type F₁I. At pH 8.0, each of the mutations caused an increase in apparent maximum inhibition and a decrease in apparentK_i relative to wild type. At pH 6.7 the hydrophilic substitutions had little effect on apparent K_i, while the hydrophobic substitutions caused increases of 3.5- to 8.5-fold relative to wild type. The ratios of apparent K_i at pH 8.0 to apparent K_i at pH 6.7 were in the range of 0.5 to 1.6 for the mutants, whereas the wild-type value is 15.0. The mutations appear to shift the equilibrium between active and inactive conformations of F₁I toward the active state. We find that H49 is required by F₁I for sensitivity to pH and that it may facilitate the transition between active and inactive states of F₁I. A possible role for H49 in the stabilization of the inactive state through participation in a multivalent complex with Zn²⁺ is also discussed.