Kinetic significance of GroEL14.(GroES7)2 complexes in molecular chaperone activity

Symmetrical GroEL14.(GroES7)2 complexes, nicknamed 'footballs', have been observed by electron microscopy to form in the presence of excess ATP. But the significance of these footballs in the molecular chaperone cycle is controversial. We have analyzed the folding of barnase in the presence of GroEL, GroES and various nucleotides to probe the importance of footballs.

A stoichiometric concentration of GroES7 binds to the GroEL14.nucleotide.denatured barnase complex to produce a slow-folding state. Higher concentrations of GroES in the presence of ATP or AMP-PNP, but not ADP, produce a proportion of a fast-folding state, rising to 50% at a GroES7:GroEL14 stoichiometry of > or = 2:1.

These results imply that there is a transiently formed GroEL14.(GroES7)2.denatured protein complex that dissociates into a 50:50 mixture of slow-folding cis and fast-folding trans GroEL14.GroES7.denatured protein complexes. The transient formation of a symmetrical football could provide a means of opening the cage that encapsulates folded cis-bound proteins.