Chloride ion binding to bacteriorhodopsin at low pH: An infrared spectroscopic study

L. Kelemen, P. Galajda, Sándor Száraz, P. Ormos

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Bacteriorhodopsin (bR) and halorhodopsin (hR) are light-induced ion pumps in the cell membrane of Halobacterium salinarium. Under normal conditions bR is an outward proton transporter, whereas hR is an inward Cl- transporter. There is strong evidence that at very low pH and in the presence of Cl-, bR transports Cl- ions into the cell, similarly to hR. The chloride pumping activity of bR is connected to the so-called acid purple state. To account for the observed effects n bR a tentative complex counterion was suggested for the protonated Schiff base of the retinal chromophore. It would consist of three charged residues: Asp-85, Asp-212, and Arg-82. This quadruplet (including the Schiff base) would also serve as a Cl- binding site at low pH. We used Fourier transform infrared difference spectroscopy to study the structural changes during the transitions between the normal, acid blue, and acid purple states. Asp-85 and Asp-212 were shown to participate in the transitions. During the normal-to-acid blue transition, Asp-85 protonates. When the pH is further lowered in the presence of Cl-, Cl- binds and Asp-212 also protonates. The binding of Cl- and the protonation of Asp-212 occur simultaneously, but take place only when Asp-85 is already protonated. It is suggested that HCl is taken up in undissociated form in exchange for a neutral water molecule.

Original languageEnglish
Pages (from-to)1951-1958
Number of pages8
JournalBiophysical Journal
Volume76
Issue number4
Publication statusPublished - 1999

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Bacteriorhodopsins
Halorhodopsins
Chlorides
Ions
Acids
Schiff Bases
Halobacterium
Ion Pumps
Ion Transport
Fourier Transform Infrared Spectroscopy
Protons
Binding Sites
Cell Membrane
Light
Water

ASJC Scopus subject areas

  • Biophysics

Cite this

Chloride ion binding to bacteriorhodopsin at low pH : An infrared spectroscopic study. / Kelemen, L.; Galajda, P.; Száraz, Sándor; Ormos, P.

In: Biophysical Journal, Vol. 76, No. 4, 1999, p. 1951-1958.

Research output: Contribution to journalArticle

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