Rhodopsin activation: effects on the metarhodopsin I-metarhodopsin II equilibrium of neutralization or introduction of charged amino acids within putative transmembrane segments.
Biochemistry
; 32(51): 14176-82, 1993 Dec 28.
Article
em En
| MEDLINE
| ID: mdl-8260503
ABSTRACT
We have studied the metarhodopsin I (M I)-metarhodopsin II (M II) equilibria of expressed wild-type and mutant rhodopsins. We studied two classes of mutants with amino acid substitutions in or near the putative transmembrane segments those in which a charged residue was replaced by a neutral residue (or in one case another charged residue) and those in which a neutral residue likely (or postulated) to be in proximity to the retinylidene Schiff's base was replaced by a charged residue. In the first class, we found mutants that abnormally favored M II (replacements of Asp-83, Glu-134, or Arg-135) as well as one that abnormally favored M I (replacement of Glu-122). In the second class, we found several mutants that abnormally favored M I, the most extreme being those in which glutamate replaced His-211 or Ala-292. These studies suggest that electrostatic forces play a major role in the energetics of the M 1-to-M II transition, and they indicate that electrostatic perturbation in the vicinity of the protonated retinylidene Schiff's base is a plausible mechanism for the change in its pKa that is associated with the M I-M II transition. They further suggest that the highly conserved pair of charged residues homologous to Glu-134 and Arg-135 may play a general role in agonist-dependent conformational changes in G-protein-coupled receptors.
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Base de dados:
MEDLINE
Assunto principal:
Rodopsina
Limite:
Animals
Idioma:
En
Ano de publicação:
1993
Tipo de documento:
Article