Chaperonin Mediated Protein Folding by Arthur Horwich YALE
GroEL is a double ring structure with each ring having seven monomers so that the complete structure has 14 monomers all bound together. The 14-mer is 165 A x 160 A cylinder. Inside chamber in resting state is about 45 A diameter. When activated (ATP binding, polypeptide binding, GroES binding) the interior chamber is about 65 A in diameter.
GroEL, GroES and ATP isolate proteins so that they can fold productively. ATP is required for non-native polypeptide to bind to hydrophobic surface inside chamber. Conformational change causes hydrophobic patches to rotate up, GroES binds at top surface like the lid of a pot to the 7-fold symmetric hydrophobic loops, and meanwhile change continues and electrostacically charged residues are turned towards the non-native polypeptide and it is as though the protein were folding all by itself in water, away from other proteins with which it might oligomerize. Then after 8-10 s, ATP is hydrolyzed, conformational change again, and GroES comes off, polypeptide (either folded or not) is released, and ADP + Pi released. Meanwhile, chamber on other side has bound ATP and is beginning another cycle of the process. ATP binding is anticooperative from one unit to another. Each unit binds two ATP in the bottom of the chamber.
Single molecule studies have shown that at infinite dilution, rate of protein folding for rubisco equals the rate of folding in GroEL showing it is a catalyst and not a machine for folding.