Abstract
TRiC/CCT is a mammalian chaperonin made up of eight distinct polypeptides arranged in two rings. TRiC changes conformation in an ATP‐dependent manner which is critical to promote protein folding in the eukaryotic cell. Unlike prokaryotic chaperonins, substrate encapsulation within the central chamber of TRiC is triggered by ATP‐induced closure of a built‐in lid.Our single particle cryo‐EM studies, including both reference‐free 2D analyses and 3D reconstructions, show the conformation variations of TRiC in different nucleotide states in the protein folding cycle. The observed changes are consistent with various biochemical evidences. Based on comparative modeling in combination with flexible fitting, pseudoatomic models have been built for each conformational state. Interestingly, in the most physiological related ATP hydrolysis transition (ADP‐AlFx) state, TRiC adopts an one ring open and one ring closed conformation. The closed ring is obviously expanded comparing to that in the closed (ATP‐AlFx) state. Notably, the inter‐domain motions in TRiC appear differently from those of prokaryotic chaperonins, despite their overall structural similarity.This research is supported through NIH Roadmap Nanomedicine Initiative grant (PN2EY016525).
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