The crystal structure of bovine cytochrome c oxidase (CcO) shows a sodium ion (Na + ) bound to the surface of subunit I. Changes in the absorption spectrum of heme a caused by calcium ions (Ca 2+ ) are detected as small red shifts, and inhibition of enzymatic activity under low turnover conditions is observed by addition of Ca 2+ in a competitive manner with Na + . In this study, we determined the crystal structure of Ca 2+ -bound bovine CcO in the oxidized and reduced states at 1.7 Å resolution. Although Ca 2+ and Na + bound to the same site of oxidized and reduced CcO, they led to different coordination geometries. Replacement of Na + with Ca 2+ caused a small structural change in the loop segments near the heme a propionate and formyl groups, resulting in spectral changes in heme a. Redox-coupled structural changes observed in the Ca 2+ -bound form were the same as those previously observed in the Na + -bound form, suggesting that binding of Ca 2+ does not severely affect enzymatic function, which depends on these structural changes. The relation between the Ca 2+ binding and the inhibitory effect during slow turnover, as well as the possible role of bound Ca 2+ are discussed.
Organizational Affiliation:
Graduate School of Science, University of Hyogo, 3-2-1 Kouto, Kamigori, Ako, Hyogo 678-1297, Japan. Electronic address: muramoto@sci.u-hyogo.ac.jp.
Graduate School of Science, University of Hyogo, 3-2-1 Kouto, Kamigori, Ako, Hyogo 678-1297, Japan. Electronic address: shinzawa@sci.u-hyogo.ac.jp.
(1S)-2-{[(2-AMINOETHOXY)(HYDROXY)PHOSPHORYL]OXY}-1-[(STEAROYLOXY)METHYL]ETHYL (5E,8E,11E,14E)-ICOSA-5,8,11,14-TETRAENOATE C43 H78 N O8 P ANRKEHNWXKCXDB-BHFWLYLHSA-N
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