The Crystal Structure of the R52Q Mutant Demonstrates a Role for R52 in Chromophore pKa Regulation in Photoactive Yellow Protein

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• 作者：Nobutaka Shimizu ; Hironari Kamikubo ; Yoichi Yamazaki ; Yasushi Imamoto ; and Mikio Kataoka
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：March 21, 2006
• 年：2006
• 卷：45
• 期：11
• 页码：3542 - 3547
• 全文大小：167K
• 年卷期：v.45,no.11(March 21, 2006)
• ISSN：1520-4995

文摘

Mutating arginine 52 to glutamine (R52Q) in photoactive yellow protein (PYP) increases thepK_a of the chromophore by 1 pH unit. The structure of the R52Q PYP mutant was determined by X-raycrystallography and was compared to the structure of wild-type PYP to assess the role of R52 in pK_aregulation. The essential differences between R52Q and the wild type were confined to the loop regioncontaining the 52nd residue. While the hydrogen bonds involving the chromophore were unchanged bythe mutation, removing the guanidino group generated a cavity near the chromophore; this cavity is occupiedby two water molecules. In the wild type, R52 forms hydrogen bonds with T50 and Y98; these hydrogenbonds are lost in R52Q. Q52 is linked to Y98 by hydrogen bonding through the two water molecules.R52 acts as a lid on the chromophore binding pocket and controls the accessibility of the exterior solventand the pK_a of the chromophore. R52 is found to flip out during the formation of PYP_M. The result of thismovement is quite similar to the altered structure of R52Q. Thus, we propose that conformational changesat R52 are partly responsible for pK_a regulation during the photocycle.