The molecular chaperones GroEL and GroES are needed to fold some proteins under what would otherwise be non-permissive conditions. The two chaperones form an asymmetrical complex that has now been crystallized and analysed by some clever mutagenic studies. The new results reveal that the substrate protein first binds to GroEL, and it is stretched apart as GroEL changes its shape. This shape change also encapsulates the substrate in a cavity within GroEL, in which it can then fold.
