Chaperonin-mediated folding in the eukaryotic cytosol proceeds through rounds of release of native and nonnative forms

Cell. 1997 Jun 13;89(6):927-37. doi: 10.1016/s0092-8674(00)80278-0.

Abstract

The eukaryotic cytosolic chaperonin, CCT, plays an essential role in mediating ATP-dependent folding of actin and tubulin. There is debate about whether it mediates folding through a single round of association followed by release of native forms, or through cycles of binding and full release in which only a fraction of released molecules reaches native form in any cycle. We examine the fate of newly synthesized substrate proteins bound to CCT in reticulocyte lysate or intact Xenopus oocytes. When a chaperonin "trap," able to bind but not release substrate protein, is introduced, production of the native state is strongly inhibited, associated with transfer to trap. While predominantly nonnative forms of actin, tubulin, and a newly identified substrate, G(alpha)-transducin, are released from CCT, a small fraction reaches native form with each round of release, inaccessible to trap. This overall mechanism resembles that of the bacterial chaperonin, GroEL.

MeSH terms

  • Actins / biosynthesis
  • Actins / chemistry*
  • Actins / metabolism
  • Animals
  • Cattle
  • Chaperonin 60 / chemistry
  • Chaperonin 60 / genetics
  • Chaperonin 60 / metabolism
  • Chaperonins / chemistry
  • Chaperonins / genetics*
  • Chaperonins / metabolism*
  • Cross-Linking Reagents / pharmacology
  • Cytosol / chemistry
  • Cytosol / metabolism
  • Eukaryotic Cells / chemistry
  • Eukaryotic Cells / physiology
  • Female
  • Humans
  • Microinjections
  • Mutagenesis / physiology
  • Oocytes / physiology
  • Protein Folding
  • Protein Synthesis Inhibitors / pharmacology
  • Recombinant Proteins / pharmacology
  • Reticulocytes / physiology
  • Transducin / chemistry
  • Transducin / metabolism
  • Tubulin / biosynthesis
  • Tubulin / chemistry
  • Tubulin / metabolism
  • Xenopus laevis

Substances

  • Actins
  • Chaperonin 60
  • Cross-Linking Reagents
  • Protein Synthesis Inhibitors
  • Recombinant Proteins
  • Tubulin
  • Chaperonins
  • Transducin