title: A local electrostatic change is the cause of the large-scale protein conformation shift in bacteriorhodopsin.
abstract: During light-driven proton transport bacteriorhodopsin shuttles between two protein conformations. A large-scale structural change similar to that in the photochemical cycle is produced in the D85N mutant upon raising the pH, even without illumination. We report here that (i) the pKa values for the change in crystallographic parameters and for deprotonation of the retinal Schiff base are the same, (ii) the retinal isomeric configuration is nearly unaffected by the protein conformation, and (iii) preventing rotation of the C13-C14 double bond by replacing the retinal with an all-trans locked analogue makes little difference to the Schiff base pKa. We conclude that the direct cause of the conformational shift is destabilization of the structure upon loss of interaction of the positively charged Schiff base with anionic residues that form its counter-ion.
authors.affiliation: Department of Physiology & Biophysics, University of California, Irvine, CA 92697-4560, USA.
authors.forename: L S
authors.initials: LS
authors.lastname: Brown
authors.forename: H
authors.initials: H
authors.lastname: Kamikubo
authors.forename: L
authors.initials: L
authors.lastname: Zimányi
authors.forename: M
authors.initials: M
authors.lastname: Kataoka
authors.forename: F
authors.initials: F
authors.lastname: Tokunaga
authors.forename: P
authors.initials: P
authors.lastname: Verdegem
authors.forename: J
authors.initials: J
authors.lastname: Lugtenburg
authors.forename: J K
authors.initials: JK
authors.lastname: Lanyi
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D007700:Kinetics; D008027:Light; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012172:Retinaldehyde / Q000378:metabolism; D012545:Schiff Bases; D013059:Spectrum Analysis, Raman; D055672:Static Electricity
chemical_list: D011994:Recombinant Proteins; D012545:Schiff Bases; D001436:Bacteriorhodopsins; D012172:Retinaldehyde