Structural visualization of the tubulin folding pathway directed by human chaperonin TRiC/CCT
- Cell. 2022 Dec 8;185(25):4770-4787.e20. doi: 10.1016/j.cell.2022.11.014.
- 1. Department of Biology, Stanford University, Stanford, CA 94305, USA.
- 2. School of Biological Sciences, Institute of Molecular Biology and Genetics, Seoul National University, Seoul, South Korea.
- 3. Department of Bioengineering, Stanford University, Stanford, CA 94305, USA.
- 4. Institute of Molecular Systems Biology, Department of Biology, ETH Zurich, 8093 Zurich, Switzerland.
- 5. School of Biological Sciences, Institute of Molecular Biology and Genetics, Seoul National University, Seoul, South Korea. Electronic address: [email protected].
- 6. Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; SSRL, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA. Electronic address: [email protected].
- 7. Department of Biology, Stanford University, Stanford, CA 94305, USA; Department of Genetics, Stanford University, Stanford, CA 94305, USA. Electronic address: [email protected].
The ATP-dependent ring-shaped chaperonin TRiC/CCT is essential for cellular proteostasis. To uncover why some eukaryotic proteins can only fold with TRiC assistance, we reconstituted the folding of β-tubulin using human prefoldin and TRiC. We find unstructured β-tubulin is delivered by prefoldin to the open TRiC chamber followed by ATP-dependent chamber closure. Cryo-EM resolves four near-atomic-resolution structures containing progressively folded β-tubulin intermediates within the closed TRiC chamber, culminating in native tubulin. This substrate folding pathway appears closely guided by site-specific interactions with conserved regions in the TRiC chamber. Initial electrostatic interactions between the TRiC interior wall and both the folded tubulin N domain and its C-terminal E-hook tail establish the native substrate topology, thus enabling C-domain folding. Intrinsically disordered CCT C termini within the chamber promote subsequent folding of tubulin's core and middle domains and GTP-binding. Thus, TRiC's chamber provides chemical and topological directives that shape the folding landscape of its obligate substrates.