The Mg2+-containing Water Cluster of Mammalian Cytochrome c Oxidase Collects Four Pumping Proton Equivalents in Each Catalytic Cycle.
Bovine heart cytochrome c oxidase (CcO) pumps four proton equivalents per catalytic cycle through the H-pathway, a proton-conducting pathway, which includes a hydrogen bond network and a water channel operating in tandem. Protons are transferred by H3O+through the water channel from the N-side into the hydrogen bond network, where they are pumped to the P-side by electrostatic repulsion between protons and net positive charges created at heme a as a result of electron donation to O2bound to heme a3To block backward proton movement, the water channel remains closed after O2binding until the sequential four-proton pumping process is complete. Thus, the hydrogen bond network must collect four proton equivalents before O2binding. However, a region with the capacity to accept four proton equivalents was not discernable in the x-ray structures of the hydrogen bond network. The present x-ray structures of oxidized/reduced bovine CcO are improved from 1.8/1.9 to 1.5/1.6 Å resolution, increasing the structural information by 1.7/1.6 times and revealing that a large water cluster, which includes a Mg2+ion, is linked to the H-pathway. The cluster contains enough proton acceptor groups to retain four proton equivalents. The redox-coupled x-ray structural changes in Glu198, which bridges the Mg2+and CuA(the initial electron acceptor from cytochrome c) sites, suggest that the CuA-Glu198-Mg2+system drives redox-coupled transfer of protons pooled in the water cluster to the H-pathway. Thus, these x-ray structures indicate that the Mg2+-containing water cluster is the crucial structural element providing the effective proton pumping in bovine CcO.
From the Picobiology Institute and.
Naomine
N
Yano
the Department of Life Science, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Akoh, Hyogo 678-1297.
Kazumasa
K
Muramoto
From the Picobiology Institute and.
Atsuhiro
A
Shimada
From the Picobiology Institute and.
Shuhei
S
Takemura
From the Picobiology Institute and.
Junpei
J
Baba
From the Picobiology Institute and.
Hidenori
H
Fujisawa
From the Picobiology Institute and.
Masao
M
Mochizuki
From the Picobiology Institute and.
Kyoko
K
Shinzawa-Itoh
the Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, and.
Eiki
E
Yamashita
From the Picobiology Institute and.|the Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, and.|JSJT, CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
Tomitake
T
Tsukihara
From the Picobiology Institute and yoshi@sci.u-hyogo.ac.jp.
Shinya
S
Yoshikawa
D000818:Animals; D002417:Cattle; D018360:Crystallography, X-Ray; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D017494:Proton Pumps / Q000737:chemistry* / Q000378:metabolism; D013329:Structure-Activity Relationship
D017494:Proton Pumps; D003576:Electron Transport Complex IV; D008274:Magnesium
bioenergetics; copper; cytochrome c oxidase (Complex IV); heme; membrane protein; mitochondrial membrane potential; proton pump; x-ray crystallography