From denaturant to ribosome: rethinking chaperone requirements in cells

Traditionally, protein refolding experiments use purified proteins that are globally unfolded with chaotropic agents or heat, whereupon chaperone-mediated refolding is scored by regained structure or activity. Yadav et al profile E. coli proteomes lacking DnaK/DnaJ or Trigger factor and find that chaperone dependence during primary biogenesis in vivo does not track with refoldability measured in vitro. Many proteins that refuse to refold after global denaturation achieve native-like structure during co-translational synthesis, while dependence on DnaK/DnaJ varies with temperature and cofactor installation. These results reposition co-translational pathways as dominant routes to native structure and argue that client lists derived from refolding assays cannot be used as simple predictors of chaperone requirements in cells.