title: Substitution of amino acids in helix F of bacteriorhodopsin: effects on the photochemical cycle.
abstract: The effects of amino acid substitutions in helix F of bacteriorhodopsin on the photocycle of this light-driven proton pump were studied. The photocycles of Ser-183----Ala and Glu-194----Gln mutants were qualitatively similar to that of wild-type bacteriorhodopsin produced in Escherichia coli and bacteriorhodopsin from Halobacterium halobium. The substitution of a Phe for either Trp-182 or Trp-189 significantly reduced the fraction of photocycling bacteriorhodopsin. The amino acid substitutions Tyr-185----Phe and Ser-193----Ala substantially increased the lifetime of the photocycle without substantially increasing the lifetime of the M photocycle intermediate. Similar results were also obtained with the Pro-186----Gly substitution. In contrast, replacing Pro-186 with the larger residue Leu inhibited the formation of the M photocycle intermediate. These results are consistent with a structural model of the retinal-binding pocket suggested by low-temperature UV/visible and Fourier transform infrared difference spectroscopies that has Trp-182, Tyr-185, Pro-186, and Trp-189 forming part of the binding pocket.
authors.affiliation: Department of Physics, Boston University, Massachusetts 02215.
authors.forename: P L
authors.initials: PL
authors.lastname: Ahl
authors.forename: L J
authors.initials: LJ
authors.lastname: Stern
authors.forename: T
authors.initials: T
authors.lastname: Mogi
authors.forename: H G
authors.initials: HG
authors.lastname: Khorana
authors.forename: K J
authors.initials: KJ
authors.lastname: Rothschild
mesh_terms: D000409:Alanine; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism*; D001436:Bacteriorhodopsins / Q000378:metabolism*; D005971:Glutamates; D018698:Glutamic Acid; D005973:Glutamine; D005998:Glycine; D006860:Hydrogen Bonding; D007700:Kinetics; D007930:Leucine; D008969:Molecular Sequence Data; D009154:Mutation; D010649:Phenylalanine; D010777:Photochemistry; D011392:Proline; D011522:Protons; D012694:Serine; D014364:Tryptophan
chemical_list: D000596:Amino Acids; D005971:Glutamates; D011522:Protons; D005973:Glutamine; D018698:Glutamic Acid; D012694:Serine; D010649:Phenylalanine; D001436:Bacteriorhodopsins; D014364:Tryptophan; D011392:Proline; D007930:Leucine; D000409:Alanine; D005998:Glycine