Snapshots of actin and tubulin folding inside the TRiC chaperonin

  • Nat Struct Mol Biol. 2022 May;29(5):420-429. doi: 10.1038/s41594-022-00755-1.
John J Kelly  1 ,  Dale Tranter  2 ,  Els Pardon  3  4 ,  Gamma Chi  1 ,  Holger Kramer  5 ,  Lotta Happonen  6 ,  Kelly M Knee  7 ,  Jay M Janz  7 ,  Jan Steyaert  3  4 ,  Christine Bulawa  7 ,  Ville O Paavilainen  2 ,  Juha T Huiskonen  8  9  10 ,  Wyatt W Yue  11  12
Affiliations
  • 1. Centre for Medicines Discovery, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
  • 2. Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, Helsinki, Finland.
  • 3. Structural Biology Brussels, Vrije Universiteit Brussel (VUB), Brussels, Belgium.
  • 4. VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium.
  • 5. Biological Mass Spectrometry and Proteomics Facility, MRC London Institute of Medical Sciences, Imperial College London, Hammersmith Hospital Campus, London, UK.
  • 6. Division of Infection Medicine, Department of Clinical Sciences, Lund University, Lund, Sweden.
  • 7. Pfizer Rare Disease Research Unit, Worldwide Research and Development, Pfizer Inc., Cambridge, MA, USA.
  • 8. Institute of Biotechnology, Helsinki Institute of Life Science HiLIFE, University of Helsinki, Helsinki, Finland. [email protected].
  • 9. Molecular and Integrative Biosciences Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland. [email protected].
  • 10. Division of Structural Biology, Wellcome Centre for Human Genetics, Roosevelt Drive, University of Oxford, Oxford, UK. [email protected].
  • 11. Centre for Medicines Discovery, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK. [email protected].
  • 12. Biosciences Institute, Medical School, Newcastle University, Newcastle upon Tyne, UK. [email protected].
PMID: 35449234 DOI: 10.1038/s41594-022-00755-1
Abstract

The integrity of a cell's proteome depends on correct folding of polypeptides by chaperonins. The chaperonin TCP-1 ring complex (TRiC) acts as obligate folder for >10% of cytosolic proteins, including he cytoskeletal proteins Actin and tubulin. Although its architecture and how it recognizes folding substrates are emerging from structural studies, the subsequent fate of substrates inside the TRiC chamber is not defined. We trapped endogenous human TRiC with substrates (Actin, tubulin) and cochaperone (PhLP2A) at different folding stages, for structure determination by cryo-EM. The already-folded regions of client proteins are anchored at the chamber wall, positioning unstructured regions toward the central space to achieve their native fold. Substrates engage with different sections of the chamber during the folding cycle, coupled to TRiC open-and-close transitions. Further, the cochaperone PhLP2A modulates folding, acting as a molecular strut between substrate and TRiC chamber. Our structural snapshots piece together an emerging model of client protein folding within TRiC.