Structure of bovine cytochrome c oxidase in the ligand‐free reduced state at neutral pH. Issue 2 (5th February 2018)

• Record Type: Journal Article
• Authors: Luo, Fangjia; Shinzawa-Itoh, Kyoko; Hagimoto, Kaede; Shimada, Atsuhiro; Shimada, Satoru; Yamashita, Eiki; Yoshikawa, Shinya; Tsukihara, Tomitake
• Is Part Of: Acta crystallographica. Volume 74:Issue 2(2018:Feb.)
• Page Start: 92
• Page End: 98
• Publication Date: 2018-02-05
• Subjects: cytochrome c oxidase -- membrane‐protein complexes -- X‐ray structure -- neutral pH; Crystallography -- Periodicals; Crystals -- Periodicals; 548
• DOI: 10.1107/S2053230X17018532
• Languages: English
• ISSNs: 2053-230X

Abstract

Abstract : Although the enzymatic activity of cytochrome c oxidase (CcO) depends sensitively on pH over a wide range, X‐ray structural analyses of bovine CcO have been conducted using crystals prepared at pH 5.7 owing to the difficulty in crystallizing this protein. Here, the structure of ligand‐free reduced CcO was successfully determined at 1.99 Å resolution. Abstract : Cytochrome c oxidase (CcO), the terminal oxidase in cellular respiration, couples proton pumping to O2 reduction. Mammalian CcO resides in the inner mitochondrial membrane. Previously, a model of H‐pathway proton pumping was proposed based on various CcO crystal structures. However, all previously determined structures were solved using crystals obtained at pH 5.7, which differs from the environmental pH of CcO in the inner membrane. The structures of fully oxidized and ligand‐free reduced CcO at pH 7.3 have now been determined. Structural comparison between the oxidized and reduced states revealed that the structural alterations that occurred upon redox change at pH 5.7 in Asp51, the magnesium‐containing cluster, haem groups and helix X, which provide important structural evidence for the H‐pathway proton‐pumping proposal, also occur at pH 7.3. These structural alterations were restricted to a local region of CcO; no domain movement was detected, nor were significant structural alterations detected in peripheral regions at either pH value. These observations indicate that the small and precise structural alterations that occur over the course of the reaction cycle are not affected by pH change, and that isolated CcO precisely performs proton pumping via the H‐pathway over a wide pH range. Because the pH is not uniform across the molecular surface of CcO, the fact that the overall structure of CcO is not affected by pH changes ensures the high enzymatic efficiency of this protein in the mitochondria.