The rhodopsin-transducin complex houses two distinct rhodopsin molecules.

ABSTRACT: Upon illumination the visual receptor rhodopsin (Rho) transitions to the activated form Rho(?), which binds the heterotrimeric G protein, transducin (Gt) causing GDP to GTP exchange and Gt dissociation. Using succinylated concanavalin A (sConA) as a probe, we visualized native Rho dimers solubilized in 1mM n-dodecyl-?-d-maltoside (DDM) and Rho monomers in 5mM DDM. By nucleotide depletion and affinity chromatography together with crosslinking and size exclusion chromatography, we trapped and purified nucleotide-free Rho(?)·Gt and sConA-Rho(?)·Gt complexes kept in solution by either DDM or lauryl-maltose-neopentyl-glycol (LMNG). The 3 D envelope calculated from projections of negatively stained Rho(?)·Gt-LMNG complexes accommodated two Rho molecules, one Gt heterotrimer and a detergent belt. Visualization of triple sConA-Rho(?)·Gt complexes unequivocally demonstrated a pentameric assembly of the Rho(?)·Gt complex in which the photoactivated Rho(?) dimer serves as a platform for binding the Gt heterotrimer. Importantly, individual monomers of the Rho(?) dimer in the heteropentameric complex exhibited different capabilities for regeneration with either 11-cis or 9-cis-retinal.

SUBMITTER: Jastrzebska B 

PROVIDER: S-EPMC3633645 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature