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FEBS Lett. 2004 Apr 30;564(3):301-6.

Crystal structures of bR(D85S) favor a model of bacteriorhodopsin as a hydroxyl-ion pump.

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Institute for Systems Biology, 1441 North 34th Street, Seattle, WA 98103, USA.


Structural features on the extracellular side of the D85S mutant of bacteriorhodopsin (bR) suggest that wild-type bR could be a hydroxyl-ion pump. A position between the protonated Schiff base and residue 85 serves as an anion-binding site in the mutant protein, and hydroxyl ions should have access to this site during the O-intermediate of the wild-type bR photocycle. The guanidinium group of R82 is proposed (1) to serve as a shuttle that eliminates the Born energy penalty for entry of an anion into this binding pocket, and conversely, (2) to block the exit of a proton or a related proton carrier.

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