The second ATP-binding site of the chaperonin GroEL and its functional role

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The Escherichia coli chaperonin GroEL, a molecular chaperone that mediates protein folding in the biological cell, expresses its chaperone function through ATP binding. In the present study, we investigated the ATP binding to GroEL by photo-affinity labeling, amino acid sequence analysis, stopped-flow fluorescence spectroscopy, and isothermal titration calorimetry. We found (1) that the second ATP-binding site is present and located near Tyr360, and (2) that in the absence of potassium ion, only the ATP binding to the primary site was observed, and its binding constant is an order of 10^4M^<-1>.