title: Functional roles of aspartic acid residues at the cytoplasmic surface of bacteriorhodopsin.
abstract: The functions of the four aspartic acid residues in interhelical loops at the cytoplasmic surface of bacteriorhodopsin, Asp-36, Asp-38, Asp-102, and Asp-104, were investigated by studying single and multiple aspartic acid to asparagine mutants. The same mutants were examined also with the additional D96N residue replacement. The kinetics of the M and N intermediates of the photochemical cycles of these recombinant proteins were affected only in a minor, although self-consistent, way. When residue 38 is an aspartate and anionic, it makes the internal proton exchange between the retinal Schiff base and Asp-96 about 3 times more rapid, and events associated with the reisomerization of retinal to all-trans about 3 times slower. Asp-36 has the opposite effect on these processes, but to a smaller extent. Asp-102 and Asp-104 have even less or none of these effects. Of the four aspartates, only Asp-36 could play a direct role in proton uptake at the cytoplasmic surface. In the 13 bacterioopsin sequences now available, only this surface aspartate is conserved.
authors.affiliation: Department of Physiology and Biophysics, University of California, Irvine 92697, USA.
authors.forename: L S
authors.initials: LS
authors.lastname: Brown
authors.forename: R
authors.initials: R
authors.lastname: Needleman
authors.forename: J K
authors.initials: JK
authors.lastname: Lanyi
mesh_terms: D000595:Amino Acid Sequence; D001216:Asparagine / Q000235:genetics; D001224:Aspartic Acid / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D001692:Biological Transport / Q000235:genetics; D017124:Conserved Sequence; D003593:Cytoplasm / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D019617:Halobacterium salinarum / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008027:Light; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010782:Photolysis; D011522:Protons; D018717:Purple Membrane / Q000737:chemistry
chemical_list: D011522:Protons; D001224:Aspartic Acid; D001436:Bacteriorhodopsins; D001216:Asparagine