E. coli GroEL chaperonin monomers, isolated after urea-induced dissociation of GroEL14, undergo cold denaturation below 5° C. Above 5°C, these monomers undergo MgATP-dependent self-assembly. We have demonstrated a conformational transition at 0°C induced by interaction of monomeric GroEL with adenine nucleotides. This conformation has a dramatically decreased Stokes radius and enhanced resistance to trypsin but it is slightly less compact than the conformation of monomers at 23°C in the absence of MgATP and it is not capable of spontaneous self-assembly. A second, temperature-dependent conformational change with a transition at about 5°C is required for GroEL to undergo oligomerization.
