• Levi J McClelland
  • Kaiming Zhang
  • Tung-Chung Mou
  • Jake Johnston
  • Cindee Yates-Hansen
  • Shanshan Li
  • Celestine J Thomas
  • Tzanko I Doukov
  • Sarah Triest
  • Alexandre Wohlkonig
  • Gregory G Tall
  • Jan Steyaert
  • Wah Chiu
  • Stephen R Sprang

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.

Original languageEnglish
Article number1077
JournalNature Communications
Issue number1
Publication statusPublished - 26 Feb 2020

ID: 49915545