In situ observation of chaperonin function in protein folding

The GroEL/GroES chaperonin mediates protein folding in bacteria in an ATP-dependent process. Studies in vitro show that the GroEL double-ring and the lid-shaped GroES transiently encapsulate unfolded protein for folding unimpaired by aggregation. To clarify critical aspects of this mechanism, we used cryo-electron tomography in situ to visualize and quantify functional GroEL:ES complexes in their intact cellular environment. Mass spectrometry was used to estimate stoichiometries of GroEL, GroES, cellular ribosome content and substrates.