Vibrational Spectroscopy of Bacteriorhodopsin Mutants: Light-Driven Proton Transport Involves Protonation Changes of Aspartic Acid Residues 85, 96, and 212

Mark S. Braiman, Tatsushi M. Mogi, Thomas M. Marti, Lawrence J. Stern, H. G. Khorana, Kenneth J. Rothschild

Research output: Contribution to journalArticle

444 Scopus citations

Abstract

Fourier transform infrared (FTIR) difference spectra have been obtained for the bR →* K, bR →° L, and bR →M photoreactions in bacteriorhodopsin mutants in which Asp residues 85, 96, 115, and 212 have been replaced by Asn and by Glu. Difference peaks that had previously been attributed to Asp COOH groups on the basis of isotopic labeling were absent or shifted in these mutants. In general, each COOH peak was affected strongly by mutation at only one of the four residues. Thus, it was possible to assign each peak tentatively to a particular Asp. From these assignments, a model for the proton-pumping mechanism of bR is derived, which features proton transfers among Asp-85, -96, and -212, the chromophore Schiff base, and other ionizable groups within the protein. The model can explain the observed COOH peaks in the FTIR difference spectra of bR photointermediates and could also account for other recent results on site-directed mutants of bR.

Original languageEnglish (US)
Pages (from-to)8516-8520
Number of pages5
JournalBiochemistry
Volume27
Issue number23
DOIs
StatePublished - Nov 1 1988

ASJC Scopus subject areas

  • Biochemistry

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