Domain-specific folding of the tandem β-propeller protein Coronin 7 (Coro7) by CCT/TRiC

Abstract

The Chaperonin containing tailless complex polypeptide 1 (CCT) or TCP-1 ring complex (TRiC) plays a central role in maintaining cellular homeostasis by supporting protein folding and damping protein aggregation. Besides the abundant cytoskeletal proteins, actin and tubulin, CCT/TRiC is emerging as an obligate chaperone for WD40 proteins, which are comprised of one or multiple {beta}-propeller domains. To date, only WD40 proteins consisting of a single {beta}-propeller domain have been described as CCT/TRiC substrates. Using a combination of biotin proximity ligation, mass spec analysis and co-immunoprecipitation, we here identify the tandem {beta}-propeller protein, Coronin 7 (Coro7), as a novel CCT/TRiC interactor. Transient knockdown of CCT/TRiC further severely diminished expression of Coro7, suggesting that Coro7 is a bona fide CCT/TRiC substrate. Interestingly, co-immunoprecipitation of truncated Coro7 proteins demonstrated that CCT/TRiC only interacts with the first {beta}-propeller domain of Coro7. In line with this, fusion of a miniTurboID tag to the N- or C-terminus of Coro7 showed significant enrichment of all CCT/TRiC subunits for the first, but not the second {beta}-propeller domain. Similarly, co-immunoprecipitation with individual Coro7 {beta}-propeller domains generated by introduction of a protease cleavage site in full length Coro7, confirmed that CCT/TRiC only binds to the first {beta}-propeller domain. Altogether, our study shows that CCT/TRiC can also function as a chaperone for multi-{beta}-propeller domain proteins, likely by initiating the folding of the first {beta}-propeller domain, which can then help template autonomous folding of consecutive {beta}-propeller domains.