6ukt
Cryo-EM structure of mammalian Ric-8A:Galpha(i):nanobody complex
Structural highlights
FunctionRIC8A_RAT Guanine nucleotide exchange factor (GEF), which can activate some, but not all, G-alpha proteins. Able to activate GNAI1, GNAO1 and GNAQ, but not GNAS by exchanging bound GDP for free GTP. Involved in regulation of microtubule pulling forces during mitotic movement of chromosomes by stimulating G(i)-alpha protein, possibly leading to release G(i)-alpha-GTP and NuMA proteins from the NuMA-GPSM2-G(i)-alpha-GDP complex. Also acts as an activator for G(q)-alpha (GNAQ) protein by enhancing the G(q)-coupled receptor-mediated ERK activation.[1] [2] Publication Abstract from PubMedRic-8A is a cytosolic Guanine Nucleotide exchange Factor (GEF) that activates heterotrimeric G protein alpha subunits (Galpha) and serves as an essential Galpha 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 Galpha 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 Galpha at multiple interfaces to form a complex that is stabilized by phosphorylation within a Ric-8A segment that connects two Galpha binding sites. The C-terminus of Galpha is ejected from its beta sheet core, thereby dismantling the GDP binding site. Ric-8A binds to the exposed Galpha beta sheet and switch II to stabilize the nucleotide-free state of Galpha. Structure of the G protein chaperone and guanine nucleotide exchange factor Ric-8A bound to Galphai1.,McClelland LJ, Zhang K, Mou TC, Johnston J, Yates-Hansen C, Li S, Thomas CJ, Doukov TI, Triest S, Wohlkonig A, Tall GG, Steyaert J, Chiu W, Sprang SR Nat Commun. 2020 Feb 26;11(1):1077. doi: 10.1038/s41467-020-14943-4. PMID:32103024[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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