Retinal isomerization in bacteriorhodopsin is controlled by specific chromophore-protein interactions. A study with noncovalent artificial pigments

A. Aharoni, M. Ottolenghi, M. Sheves

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

It has previously been shown that, in mutants lacking the Lys-216 residue, protonated Schiff bases of retinal occupy noncovalently the bacteriorhodopsin (bR) binding site. Moreover, the retinal-Lys-216 covalent bond is not a prerequisite for initiating the photochemical and proton pump activity of the pigment. In the present work, various Schiff bases of aromatic polyene chromophores were incubated with bacterioopsin to give noncovalent pigments that retain the Lys-216 residue in the binding site. It was observed that the pigment's absorption was considerably red-shifted relative to the corresponding protonated Schiff bases (PSB) in solution and was sensitive to Schiff base linkage substitution. Their PSB pKa is considerably elevated, similarly to those of related covalently bound pigments. However, the characteristic low-pH purple to blue transition is not observed, but rather a chromophore release from the binding site takes place that is characterized by a pKa of ∼6 (sensitive to the specific complex). It is suggested that, in variance with native bR, in these complexes Asp-85 is protonated and Asp-212 serves as the sole negatively charged counterion. In contrast to the bound analogues, no photocycle could be detected. It is suggested that a specific retinal-protein geometrical arrangement in the binding site is a prerequisite for achieving the selective retinal photoisomerization.

Original languageEnglish
Pages (from-to)13310-13319
Number of pages10
JournalBiochemistry
Volume40
Issue number44
DOIs
StatePublished - 6 Nov 2001
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry

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