TY - JOUR
T1 - Pathways for proton release during ubihydroquinone oxidation by the bc1 complex
AU - Crofts, Antony R.
AU - Hong, Sangjin
AU - Ugulava, Natalia
AU - Barquera, Blanca
AU - Gennis, Robert
AU - Guergova-Kuras, Mariana
AU - Berry, Edward A.
PY - 1999/8/31
Y1 - 1999/8/31
N2 - Quinol oxidation by the bc1 complex of Rhodobacter sphaeroides occurs from an enzyme-substrate complex formed between quinol bound at the Q0 site and the iron-sulfur protein (ISP) docked at an interface on cytochrome b. From the structure of the stigmatellin-containing mitochondrial complex, we suggest that hydrogen bonds to the two quinol hydroxyl groups, from Glu-272 of cytochrome b and His-161 of the ISP, help to stabilize the enzyme- substrate complex and aid proton release. Reduction of the oxidized ISP involves H transfer from quinol. Release of the proton occurs when the acceptor chain reoxidizes the reduced ISP, after domain movement to an interface on cytochrome c1. Effects of mutations to the ISP that change the redox potential and/or the pK on the oxidized form support this mechanism. Structures for the complex in the presence of inhibitors show two different orientations of Glu-272. In stigmatellin-containing crystals, the side chain points into the site, to hydrogen bond with a ring hydroxyl, while His-161 hydrogen bonds to the carbonyl group. In the native structure, or crystals containing myxothiazol or β-methoxyacrylate-type inhibitors, the Glu272 side chain is rotated to point out of the site, to the surface of an external aqueous channel. Effects of mutation at this residue suggest that this group is involved in ligation of stigmatellin and quinol, but not quinone, and that the carboxylate function is essential for rapid turnover. H+ transfer from semiquinone to the carboxylate side chain and rotation to the position found in the myxothiazol structure provide a pathway for release of the second proton.
AB - Quinol oxidation by the bc1 complex of Rhodobacter sphaeroides occurs from an enzyme-substrate complex formed between quinol bound at the Q0 site and the iron-sulfur protein (ISP) docked at an interface on cytochrome b. From the structure of the stigmatellin-containing mitochondrial complex, we suggest that hydrogen bonds to the two quinol hydroxyl groups, from Glu-272 of cytochrome b and His-161 of the ISP, help to stabilize the enzyme- substrate complex and aid proton release. Reduction of the oxidized ISP involves H transfer from quinol. Release of the proton occurs when the acceptor chain reoxidizes the reduced ISP, after domain movement to an interface on cytochrome c1. Effects of mutations to the ISP that change the redox potential and/or the pK on the oxidized form support this mechanism. Structures for the complex in the presence of inhibitors show two different orientations of Glu-272. In stigmatellin-containing crystals, the side chain points into the site, to hydrogen bond with a ring hydroxyl, while His-161 hydrogen bonds to the carbonyl group. In the native structure, or crystals containing myxothiazol or β-methoxyacrylate-type inhibitors, the Glu272 side chain is rotated to point out of the site, to the surface of an external aqueous channel. Effects of mutation at this residue suggest that this group is involved in ligation of stigmatellin and quinol, but not quinone, and that the carboxylate function is essential for rapid turnover. H+ transfer from semiquinone to the carboxylate side chain and rotation to the position found in the myxothiazol structure provide a pathway for release of the second proton.
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U2 - 10.1073/pnas.96.18.10021
DO - 10.1073/pnas.96.18.10021
M3 - Article
C2 - 10468555
AN - SCOPUS:0033621166
SN - 0027-8424
VL - 96
SP - 10021
EP - 10026
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 18
ER -