title: Effect of substitution of proline-77 to aspartate on the light-driven proton release of bacteriorhodopsin.
abstract: Wild-type bacteriorhodopsin (BR) and another retinal protein archaerhodopsin 4 (AR4) are both light-driven proton pumps, but exhibit opposite temporal orders of proton release and uptake upon a flash illumination at neutral pH due to a higher pK(a)  of proton release complex (PRC) in AR4. Since the 77th residue in the extracellular side is proline (P) in BR, but aspartic acid (D) in AR4, we have mutated P77 in BR by D in this study. The new point mutation was found to affect the kinetics of proton release and the pH dependence significantly. Upon a flash excitation, three components "fast proton release,""proton uptake" and "slow proton release" were observed at neutral pH in P77D. The pK(a)  of PRC in the M intermediate was increased from 5.6 in the wild-type to 7.0, and became closer to that in AR4, which is 8.4. The coupling strength between D85 and PRC were also weakened, as expected. These data indicate that the 77th residue in AR4 greatly account for the difference between the two proton pumps.
authors.affiliation: State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Advanced Materials Laboratory, Fudan University, Shanghai, China.
authors.forename: Yazhuo
authors.initials: Y
authors.lastname: Wang
authors.forename: Yingchun
authors.initials: Y
authors.lastname: Zhao
authors.forename: Ming
authors.initials: M
authors.lastname: Ming
authors.forename: Jia
authors.initials: J
authors.lastname: Wu
authors.forename: Weida
authors.initials: W
authors.lastname: Huang
authors.forename: Jiandong
authors.initials: J
authors.lastname: Ding
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001224:Aspartic Acid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D055664:Electrochemical Techniques; D015870:Gene Expression; D019617:Halobacterium salinarum / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011392:Proline / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011522:Protons; D013329:Structure-Activity Relationship; D017494:Proton Pumps
chemical_list: D019843:Archaeal Proteins; D001224:Aspartic Acid; D001436:Bacteriorhodopsins; D011392:Proline; D011522:Protons; C055476:archaerhodopsin protein, Archaea; D017494:Proton Pumps