Structure of the G protein chaperone and guanine nucleotide exchange factor Ric-8A bound to Gαi1

Nat Commun. 2020 Feb 26;11(1):1077. doi: 10.1038/s41467-020-14943-4.


Ric-8A is a cytosolic Guanine Nucleotide exchange Factor (GEF) that activates heterotrimeric G protein alpha subunits (Gα) and serves as an essential Gα chaperone. Mechanisms by which Ric-8A catalyzes these activities, which are stimulated by Casein Kinase II phosphorylation, are unknown. We report the structure of the nanobody-stabilized complex of nucleotide-free Gα bound to phosphorylated Ric-8A at near atomic resolution by cryo-electron microscopy and X-ray crystallography. The mechanism of Ric-8A GEF activity differs considerably from that employed by G protein-coupled receptors at the plasma membrane. Ric-8A engages a specific conformation of Gα at multiple interfaces to form a complex that is stabilized by phosphorylation within a Ric-8A segment that connects two Gα binding sites. The C-terminus of Gα is ejected from its beta sheet core, thereby dismantling the GDP binding site. Ric-8A binds to the exposed Gα beta sheet and switch II to stabilize the nucleotide-free state of Gα.

Publication types

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

MeSH terms

  • Animals
  • Asymmetric Cell Division / physiology
  • Binding Sites / physiology
  • Camelids, New World
  • Casein Kinase II / metabolism*
  • Cell Membrane / metabolism
  • Cryoelectron Microscopy
  • Crystallography, X-Ray
  • Embryonic Development / physiology
  • GTP-Binding Protein alpha Subunits / metabolism*
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Molecular Chaperones / metabolism
  • Multiprotein Complexes / ultrastructure
  • Phosphorylation
  • Protein Binding / physiology
  • Protein Conformation


  • GTP-Binding Protein alpha Subunits
  • Guanine Nucleotide Exchange Factors
  • Molecular Chaperones
  • Multiprotein Complexes
  • Casein Kinase II