Conserved Glycine 232 in the Ligand Channel of ba3 Cytochrome Oxidase from Thermus thermophilus

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• 作者：William McDonald ; Chie Funatogawa ; Yang Li ; Ying Chen ; Istvan Szundi ; James A. Fee ; C. David Stout ; 脫l枚f Einarsd贸ttir
• 刊名：Biochemistry
• 出版年：2014
• 出版时间：July 15, 2014
• 年：2014
• 卷：53
• 期：27
• 页码：4467-4475
• 全文大小：629K
• ISSN：1520-4995

文摘

Knowing how the protein environment modulates ligand pathways and redox centers in the respiratory heme-copper oxidases is fundamental for understanding the relationship between the structure and function of these enzymes. In this study, we investigated the reactions of O₂ and NO with the fully reduced G232V mutant of ba₃ cytochrome c oxidase from Thermus thermophilus (Tt ba₃) in which a conserved glycine residue in the O₂ channel of the enzyme was replaced with a bulkier valine residue. Previous studies of the homologous mutant of Rhodobacter sphaeroides aa₃ cytochrome c oxidase suggested that the valine completely blocked the access of O₂ to the active site [Salomonsson, L., et al. (2004) Proc. Natl. Acad. Sci. U.S.A. 101, 11617鈥?1621]. Using photolabile O₂ and NO carriers, we find by using time-resolved optical absorption spectroscopy that the rates of O₂ and NO binding are not significantly affected in the Tt ba₃ G232V mutant. Classical molecular dynamics simulations of diffusion of O₂ to the active site in the wild-type enzyme and G232V mutant show that the insertion of the larger valine residue in place of the glycine appears to open up other O₂ and NO exit/entrance pathways that allow these ligands unhindered access to the active site, thus compensating for the larger valine residue.