The GroEL chaperonin: a protein machine with pistons driven by ATP binding and hydrolysis.

In response to the binding of ATP, the two heptameric rings of the GroEL chaperonin protein interact with one another in a negatively cooperative manner. Owing to the helix dipole, the positively charged nitrogen of glycine 88 at the N-terminus of helix D binds to oxygen atoms on the β and γ phosphorus atoms of ATP. In apo-GroEL, the nucleotide-binding sites of different rings are connected to one another by the interaction of the ɛ-amino group of lysine 105 of one helix D across the twofold axis with the negatively charged carbonyl oxygen atom of alanine 109 at the C-terminus of the other helix D. Upon binding ATP, the K105-A109 salt bridge breaks and both helices move apart by approximately 3.5 Å en bloc toward the ATP. Upon hydrolysis of ATP, the helices return to their original position. The helices thus behave as pistons, their movement being driven by the binding and hydrolysis of ATP.This article is part of a discussion meeting issue 'Allostery and molecular machines'.