title: Reversal of the surface charge asymmetry in purple membrane due to single amino acid substitutions.
abstract: Twenty-seven mutant bacteriorhodopsin's were screened to determine the PKa for reversal of the permanent electric dipole moment. The photoelectric response of an aqueous purple-membrane suspension was used to determine the direction of the purple-membrane dipole moment as a function of pH. The pK(a) for the dipole reversal of wild-type bacteriorhodopsin is 4.5. Six of the 27 mutant bacteriorhodopsin's were found to have a pK(a) for dipole reversal larger than that of wild-type bacteriorhodopsin. Two of these mutants, L93T and L93W, involve a neutral amino acid substitution in the interior of the protein. The direction of the purple-membrane permanent electric dipole moment is determined by the purple-membrane surface charge asymmetry. We conclude that these two substitutions, which do not involve charge replacement, alter the pK(a) for the reversal of the purple-membrane surface charge asymmetry. We suggest that these changes to the pK(a) are due to altered protein folding at the surface of the purple-membrane induced by single-site substitutions in the protein interior.
authors.affiliation: Physics Department, University of Oregon, Eugene 97403, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Hsu
authors.forename: G W
authors.initials: GW
authors.lastname: Rayfield
authors.forename: R
authors.initials: R
authors.lastname: Needleman
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D003624:Darkness; D004563:Electrochemistry; D006217:Halobacterium / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D016297:Mutagenesis, Site-Directed; D010777:Photochemistry; D017354:Point Mutation; D018717:Purple Membrane / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013053:Spectrophotometry; D013499:Surface Properties; D013997:Time Factors
chemical_list: D011994:Recombinant Proteins; D001436:Bacteriorhodopsins