1iw9

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spinqualitylabelsall models 1iw9, resolution 2.5Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal Structure of the M Intermediate of Bacteriorhodopsin

Overview

Structural changes in the proton pumping cycle of wild-type, bacteriorhodopsin were investigated by using a 3D crystal (space group, P622)prepared by the membrane fusion method. Protein-protein contacts in, the crystal elongate the lifetime of the M intermediate by a factor of, approximately 100,allowing high levels of the M intermediate to accumulate, under continuous illumination. When the M intermediate generated at room, temperature was exposed to a low flux of X-rays (approximately 10(14), photons/mm2), this yellow intermediate was converted into a blue species, having an absorption maximum at 650 nm. This color change is suggested to, accompany a configuration change in the retinal-Lys216 chain. The true, conformational change associated with formation of the M intermediate was, analyzed by taking the X-radiation-induced structural change into account., Our result indicates that, upon formation of the M intermediate, helix G, move stowards the extra-cellular side by, on average, 0.5 angstroms. This, movement is coupled with several reactions occurring at distal sites in, the protein: (1) reorientation of the side-chain of Leu93 contacting the, C13 methyl group of retinal, which is accompanied by detachment of a water, molecule from the Schiff base; (2) a significant distortion in the F-G, loop, triggering destruction of a hydrogen bonding interaction between a, pair of glutamate groups (Glu194 and Glu204); (3) formation of a salt, bridge between the carboxylate group of Glu204 and the guanidinium ion of, Arg82, which is accompanied by a large distortion in the extra-cellular, half of helix C; (4)noticeable movements of the AB loop and the, cytoplasmic end of helix B. But, no appreciable change is induced in the, peptide backbone of helices A,D, E and F. These structural changes are, discussed from the viewpoint of translocation of water molecules.

About this Structure

1IW9 is a Single protein structure of sequence from Halobacterium salinarum with RET, L3P and L2P as ligands. Full crystallographic information is available from OCA.

Reference

Crystal structure of the M intermediate of bacteriorhodopsin: allosteric structural changes mediated by sliding movement of a transmembrane helix., Takeda K, Matsui Y, Kamiya N, Adachi S, Okumura H, Kouyama T, J Mol Biol. 2004 Aug 20;341(4):1023-37. PMID:15328615

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