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Experimental evidence for secondary protein-chromophore interactions at the Schiff base linkage in bacteriorhodopsin: molecular mechanism for proton pumping

Journal Article · · Proc. Natl. Acad. Sci. U.S.A.; (United States)
; ; ;
Resonance Raman spectroscopy of the retinylidene chromophore in various isotopically labeled membrane environments together with spectra of isotopically labeled model compounds demonstrates that a secondary protein interaction is present at the protonated Schiff base linkage in bacteriorhodopsin. The data indicate that although the interaction is present in all protonated bacteriorhodopsin species it is absent in unprotonated intermediates. Furthermore, kinetic resonance Raman spectroscopy has been used to monitor the dynamics of Schiff base deprotonation as a function of pH. All results are consistent with lysine as the interacting group. A structure for the interaction is proposed in which the interacting protein group in an unprotonated configuration is complexed through the Schiff base proton to the Schiff base nitrogen. These data suggest a molecular mechanism for proton pumping and ion gate molecular regulation. In this mechanism, light causes electron redistribution in the retinylidene chromophore, which results in the deprotonation of an amino acid side chain with pK > 10.2 +- 0.3 (e.g., arginine). This induces subsequent retinal and protein conformational transitions which eventually lower the pK of the Schiff base complex from > 12 before light absorption to 10.2 +- 0.3 in microseconds after photon absorption. Finally, in this low pK state the complex can reprotonate the proton-deficient high pK group generated by light, and the complex is then reprotonated from the opposite side of the membrane.
Research Organization:
Argonne National Lab., IL
OSTI ID:
5884236
Journal Information:
Proc. Natl. Acad. Sci. U.S.A.; (United States), Journal Name: Proc. Natl. Acad. Sci. U.S.A.; (United States) Vol. 75:10; ISSN PNASA
Country of Publication:
United States
Language:
English

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Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
BACTERIA
BARYONS
BIOCHEMICAL REACTION KINETICS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CELL MEMBRANES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
FERMIONS
HADRONS
IMINES
KINETICS
LABELLED COMPOUNDS
LYSINE
MASSLESS PARTICLES
MEMBRANE TRANSPORT
MEMBRANES
MICROORGANISMS
MOLECULAR BIOLOGY
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTONS
PIGMENTS
PROTEINS
PROTONS
RADIATIONS
RAMAN SPECTRA
REACTION KINETICS
SCHIFF BASES
SPECTRA
SPECTROSCOPY
VISIBLE RADIATION