We have analyzed crystal structures of cytochrome bc1 complexes with electron transfer inhibitors bound to the ubiquinone binding pockets Q(i) and/or Q(o) in the cytochrome b subunit. The presence or absence of the Q(i) inhibitor antimycin A did not affect the binding of the Q(o) inhibitors. Different subtypes of Q(o) inhibitors had dramatically different effects on the mobility of the extramembrane domain of the iron-sulfur protein (ISP): Binding of 5-undecyl-6-hydroxy-4,7-dioxobenzothiazol and stigmatellin (subtype Q(o)-II and Q(o)-III, respectively) led to a fixation of the ISP domain on the surface of cytochrome b, whereas binding of myxothiazol and methoxyacrylate-stilbene (subtype Q(o)-I) favored release of this domain. The native structure has an empty Q(o) pocket and is intermediate between these extremes. On the basis of these observations we propose a model of quinone oxidation in the bc1 complex, which incorporates fixed and loose states of the ISP as features important for electron transfer and, possibly, also proton transport.
|Original language||English (US)|
|Number of pages||8|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Publication status||Published - Jul 7 1998|
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