title: Evidence for charge-controlled conformational changes in the photocycle of bacteriorhodopsin.
abstract: The existence of two different M-state structures in the photocycle of the bacteriorhodopsin mutant ASP38ARG was proved. At pH 6.7 (0 to -6 degreesC) a spectroscopic M intermediate (M1) that does not differ significantly in its tertiary structure from the light-adapted ground state accumulates under illumination. At pH > 9 another state (M2), characterized by additional pronounced changes in the Fourier transform infrared difference spectrum in the region of the amide I and II bands, accumulates. The M2 intermediate trapped at pH 9.6 displays the same changes in the x-ray diffraction intensities under continuous illumination as previously described for x-ray experiments with the mutant ASP96ASN. These observations indicate that in this mutant the altered charge distribution at neutral pH controls the tertiary structural changes that seem to be necessary for proton translocation.
authors.affiliation: Forschungszentrum Jülich, IBI-2, Structural Biology, D-52425 Jülich, Germany. Jurgen@ibistr.dnet.kfa-juelich.de
authors.forename: H J
authors.initials: HJ
authors.lastname: Sass
authors.forename: R
authors.initials: R
authors.lastname: Gessenich
authors.forename: M H
authors.initials: MH
authors.lastname: Koch
authors.forename: D
authors.initials: D
authors.lastname: Oesterhelt
authors.forename: N A
authors.initials: NA
authors.lastname: Dencher
authors.forename: G
authors.initials: G
authors.lastname: Büldt
authors.forename: G
authors.initials: G
authors.lastname: Rapp
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects; D055592:Biophysical Phenomena; D001703:Biophysics; D004563:Electrochemistry; D019617:Halobacterium salinarum / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D008027:Light; D016297:Mutagenesis, Site-Directed; D010777:Photochemistry; D011487:Protein Conformation; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
chemical_list: D001436:Bacteriorhodopsins