1f4z

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BACTERIORHODOPSIN-M PHOTOINTERMEDIATE STATE OF THE E204Q MUTANT AT 1.8 ANGSTROM RESOLUTION

Overview

In order to understand how isomerization of the retinal drives, unidirectional transmembrane ion transport in bacteriorhodopsin, we, determined the atomic structures of the BR state and M photointermediate, of the E204Q mutant, to 1.7 and 1.8 A resolution, respectively. Comparison, of this M, in which proton release to the extracellular surface is, blocked, with the previously determined M in the D96N mutant indicates, that the changes in the extracellular region are initiated by changes in, the electrostatic interactions of the retinal Schiff base with Asp85 and, Asp212, but those on the cytoplasmic side originate from steric conflict, of the 13-methyl retinal group with Trp182 and distortion of the pi-bulge, of helix G. The structural changes suggest that protonation of Asp85, initiates a cascade of atomic displacements in the extracellular region, that cause release of a proton to the surface. The progressive relaxation, of the strained 13-cis retinal chain with deprotonated Schiff base, in, turn, initiates atomic displacements in the cytoplasmic region that cause, the intercalation of a hydrogen-bonded water molecule between Thr46 and, Asp96. This accounts for the lowering of the pK(a) of Asp96, which then, reprotonates the Schiff base via a newly formed chain of water molecules, that is extending toward the Schiff base.

About this Structure

1F4Z is a Single protein structure of sequence from Halobacterium salinarum with LI1, SQU and RET as ligands. Full crystallographic information is available from OCA.

Reference

Coupling photoisomerization of retinal to directional transport in bacteriorhodopsin., Luecke H, Schobert B, Cartailler JP, Richter HT, Rosengarth A, Needleman R, Lanyi JK, J Mol Biol. 2000 Jul 28;300(5):1237-55. PMID:10903866

Page seeded by OCA on Tue Nov 20 14:37:20 2007