Coordination of CuB in reduced and CO-liganded states of cytochrome bo3 from Escherichia coli. Is chloride ion a cofactor?
Coordination of CuB in reduced and CO-liganded states of cytochrome bo3 from Escherichia coli. Is chloride ion a cofactor?
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大肠杆菌细胞色素 bo3 的还原态和共配体态中 CuB 的协调。
DOI：
10.1021/bi982885l
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Blackburn,NJ
中科院分区：
文献类型：
--
作者：
Ralle,M;Verkhovskaya,ML;Morgan,JE;Verkhovsky,MI;Wikstrom,M;Blackburn,NJ
The ubiquinol oxidase cytochromebo3fromEscherichia coliis one of the respiratory heme−copper oxidases which catalyze the reduction of O2to water linked to translocation of protons across the bacterial or mitochondrial membrane. We have studied the structure of the CuBsite in the binuclear heme−copper center of O2reduction by EXAFS spectroscopy in the fully reduced state of this enzyme, as well as in the reduced CO-liganded states where CO is bound either to the heme iron or to CuB. We find that, in the reduced enzyme, CuBis coordinated by one weakly bound and two strongly bound histidine imidazoles at Cu−N distances of 2.10 and 1.92 Å, respectively, and that an additional feature at 2.54 Å is due to a highly ordered water molecule that might be weakly associated with the copper. Unexpectedly, the binding of CO to heme iron is found to result in a major conformational change at CuB, which now binds only two equidistant histidine imidazoles at 1.95 Å and a chloride ion at 2.25 Å, with elimination of the water molecule and one of the histidines. Attempts to remove the chloride from the enzyme by extensive dialysis did not change this finding, nor did substitution of chloride with bromide. Photolysis of CO bound to the heme iron is known to cause the CO to bind to CuBin a very fast reaction and to remain bound to CuBat low temperatures. In this state, we indeed find the CO to be bound to CuBat a Cu−C distance of 1.85 Å, with chloride still bound at 2.25 Å and the two histidine imidazoles at a Cu−N distance of 2.01 Å. These results suggest that reduction of the binuclear site weakens the bond between CuBand one of its three histidine imidazole ligands, and that binding of CO to the reduced binuclear site causes a major structural change in CuBin which one histidine ligand is lost and replaced by a chloride ion. Whether chloride is a cofactor in this enzyme is discussed.
