Isolation and functional characterization of a stable complex between photoactivated rhodopsin and the G protein, transducin

FASEB J. 2009 Feb;23(2):371-81. doi: 10.1096/fj.07-114835. Epub 2008 Sep 30.

Abstract

Transitory binding between photoactivated rhodopsin (Rho* or Meta II) and the G protein transducin (Gt-GDP) is the first step in the visual signaling cascade. Light causes photoisomerization of the 11-cis-retinylidene chromophore in rhodopsin (Rho) to all-trans-retinylidene, which induces conformational changes that allow Gt-GDP to dock onto the Rho* surface. GDP then dissociates from Gt, leaving a transient nucleotide-empty Rho*-Gt(e) complex before GTP becomes bound, and Gt-GTP then dissociates from Rho*. Further biochemical advances are required before structural studies of the various Rho*-Gt complexes can be initiated. Here, we describe the isolation of n-dodecyl-beta-maltoside solubilized, stable, functionally active, Rho*-Gt(e), Rho(e)*-Gt(e), and 9-cis-retinal/11-cis-retinal regenerated Rho-Gt(e) complexes by sucrose gradient centrifugation. In these complexes, Rho* spectrally remained in its Meta II state, and Gt(e) retained its ability to interact with GTPgammaS. Removal of all-trans-retinylidene from Rho*-Gt(e) had no effect on the stability of the Rho(e)*-Gt(e) complex. Moreover, opsin in the Rho(e)*-Gt(e) complex with an empty nucleotide-binding pocket in Gt and an empty retinoid-binding pocket in Rho was regenerated up to 75% without complex dissociation. These results indicate that once Rho* couples with Gt, the chromophore plays a minor role in stabilizing this complex. Moreover, in complexes regenerated with 9-cis-retinal/11-cis-retinal, Rho retains a conformation similar to Rho* that is stabilized by Gt(e) apo-protein.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cattle
  • Microscopy, Electron, Transmission
  • Photochemistry
  • Protein Binding
  • Rhodopsin / genetics
  • Rhodopsin / isolation & purification*
  • Rhodopsin / metabolism*
  • Rhodopsin / ultrastructure
  • Solubility
  • Transducin / isolation & purification*
  • Transducin / metabolism*
  • Transducin / ultrastructure

Substances

  • Rhodopsin
  • Transducin