G protein subtype specificity of rhodopsin intermediates metarhodopsin Ib and metarhodopsin II

Photochem Photobiol. 2009 Jan-Feb;85(1):57-62. doi: 10.1111/j.1751-1097.2008.00396.x. Epub 2008 Jul 17.

Abstract

Rhodopsin is one of the members of the G protein-coupled receptor family that can catalyze a GDP-GTP exchange reaction on the retinal G protein transducin (Gt) upon photon absorption. There are at least two intermediate states, meta-Ib and meta-II, which exhibit direct interaction with Gt. Meta-Ib binds to GDP-bound Gt, while meta-II forms a complex with Gt having no nucleotide, suggesting that meta-Ib is a state that initially interacts with Gt. Here we investigated whether or not meta-Ib exhibits specific interaction with G protein similar to meta-II, by examining the binding efficiencies of meta-Ib and meta-II to Gialpha and its mutants whose C-terminal 11 amino acids were replaced with those of Goalpha, Gqalpha and Gsalpha. The affinity of meta-Ib to the C-terminal 11 amino acids of Gtalpha was similar to those of Gialpha and its mutant with Goalpha's C-terminal 11 amino acids, whereas meta-II exhibited affinity to the C-terminal 11 amino acids of Gialpha mutant with Goalpha's C-terminal 11 amino acids about half of what was seen for Gtalpha and Gialpha. Both intermediates exhibited no affinity to the Gialpha mutants containing the C-terminal 11 amino acids of Gqalpha and Gsalpha. These results suggested that meta-Ib is the state that exhibits specific interaction with G protein as meta-II does, although meta-Ib exhibits a slightly lenient binding selectivity compared to that of meta-II.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • GTP-Binding Proteins / chemistry
  • GTP-Binding Proteins / classification
  • GTP-Binding Proteins / genetics
  • GTP-Binding Proteins / metabolism*
  • Mutation / genetics
  • Protein Binding
  • Rats
  • Rhodopsin / classification
  • Rhodopsin / metabolism*
  • Substrate Specificity
  • Temperature

Substances

  • Rhodopsin
  • GTP-Binding Proteins