(697.11) Structural analysis of G protein β5 subunit folding by the cytosolic chaperonin CCT/TRiC and its co-chaperone phosducin-like protein 1 reveal molecular mechanisms of chaperone-mediated β-propeller protein folding

Poster Board Number: B93

Mikaila Sass (Brigham Young University), William Ludlam (Brigham Young University), Shuxin Wang (University of Utah School of Medicine), Yujin Kwon (Brigham Young University), Ethan Carter (Brigham Young University), Joseph Bohman (Brigham Young University), Peter Shen (University of Utah School of Medicine), Barry Willardson (Brigham Young University)

The cytosolic chaperonin CCT and its co-chaperone phosducin-like protein 1 (PhLP1) play important roles in G protein complex assembly by folding G protein b subunits (Gb) into b-propeller structures. To understand this process at the molecular level, we have isolated the CCT-Gb5-PhLP1 folding intermediate in both the open and closed CCT conformations and determined its structure by high resolution cryo-electron microscopy (cryo-EM).  In the open structures, Gβ5 interact with the N- and C-termini of the CCT subunits deep inside the folding chamber between the CCT rings in a closed b-propeller conformation.  PhLP1 allosterically enhances Gb5 binding to CCT by interacting with the CCT apical domains at the rim of the folding chamber without contacting Gb5 directly.  In the closed CCT structures, Gb5 move from between the CCT rings into one of the folding chambers, suggesting a path for release of Gb5 from CCT during its ATPase cycle.  These findings provide a molecular explanation for CCT-dependent folding and release of Gb5 to interact with RGS proteins and perform their essential functions in G protein signaling.

National Institute of Health grant R01EY012287