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Structure of the M Intermediate of Bacteriorhodopsin trapped at 100K
Structural highlights
FunctionBACR_HALSA Light-driven proton pump. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedStructural 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. 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[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences | ||||||||||||||||||||
