Structural changes in bacteriorhodopsin during ion transport at 2 angstrom resolution.

Luecke H, Schobert B, Richter HT, Cartailler JP, Lanyi JK
Science. 1999 286 (5438): 255-61

PMID: 10514362 · DOI:10.1126/science.286.5438.255

Crystal structures of the Asp96 to Asn mutant of the light-driven proton pump bacteriorhodopsin and its M photointermediate produced by illumination at ambient temperature have been determined to 1.8 and 2.0 angstroms resolution, respectively. The trapped photoproduct corresponds to the late M state in the transport cycle-that is, after proton transfer to Asp85 and release of a proton to the extracellular membrane surface, but before reprotonation of the deprotonated retinal Schiff base. Its density map describes displacements of side chains near the retinal induced by its photoisomerization to 13-cis,15-anti and an extensive rearrangement of the three-dimensional network of hydrogen-bonded residues and bound water that accounts for the changed pKa values (where Ka is the acid constant) of the Schiff base and Asp85. The structural changes detected suggest the means for conserving energy at the active site and for ensuring the directionality of proton translocation.

MeSH Terms (21)

Bacteriorhodopsins Binding Sites Crystallography, X-Ray Cytoplasm Hydrogen-Ion Concentration Hydrogen Bonding Ion Transport Isomerism Light Models, Molecular Photolysis Photons Point Mutation Protein Conformation Protein Structure, Secondary Proton Pumps Protons Retinaldehyde Schiff Bases Thermodynamics Water

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