Structures of the Rhodopsin-Transducin Complex: Insights into G-Protein Activation

Mol Cell. 2019 Aug 22;75(4):781-790.e3. doi: 10.1016/j.molcel.2019.06.007. Epub 2019 Jul 9.


Rhodopsin (Rho), a prototypical G-protein-coupled receptor (GPCR) in vertebrate vision, activates the G-protein transducin (GT) by catalyzing GDP-GTP exchange on its α subunit (GαT). To elucidate the determinants of GT coupling and activation, we obtained cryo-EM structures of a fully functional, light-activated Rho-GT complex in the presence and absence of a G-protein-stabilizing nanobody. The structures illustrate how GT overcomes its low basal activity by engaging activated Rho in a conformation distinct from other GPCR-G-protein complexes. Moreover, the nanobody-free structures reveal native conformations of G-protein components and capture three distinct conformers showing the GαT helical domain (αHD) contacting the Gβγ subunits. These findings uncover the molecular underpinnings of G-protein activation by visual rhodopsin and shed new light on the role played by Gβγ during receptor-catalyzed nucleotide exchange.

Keywords: G-protein; GPCR; GPCR-G-protein complex; cryo-EM; phototransduction; rhodopsin; transducing.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Cattle
  • Cryoelectron Microscopy
  • Multiprotein Complexes / chemistry*
  • Multiprotein Complexes / metabolism
  • Multiprotein Complexes / ultrastructure
  • Protein Domains
  • Protein Structure, Secondary
  • Rhodopsin / chemistry*
  • Rhodopsin / metabolism
  • Transducin / chemistry*
  • Transducin / metabolism


  • Multiprotein Complexes
  • Rhodopsin
  • Transducin