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The eukaryotic chaperonin TRiC/CCT assists the folding of about 10% of cytosolic proteins through an ATP-driven conformational cycle, and the essential cytoskeleton protein tubulin is the obligate substrate of TRiC. Here, we present an ensemble of cryo-EM structures of endogenous human TRiC throughout its ATPase cycle, with three of them revealing endogenously engaged tubulin in different folding stages. The open-state TRiC-tubulin-S1 and -S2 maps show extra density corresponding to tubulin in the cis-ring chamber of TRiC. Our structural and XL-MS analyses suggest a gradual upward translocation and stabilization of tubulin within the TRiC chamber accompanying TRiC ring closure. In the closed TRiC-tubulin-S3 map, we capture a near-natively folded tubulin—with the tubulin engaging through its N and C domains mainly with the A and I domains of the CCT3/6/8 subunits through electrostatic and …