Chaperonins are nano-machines that are built of two back-to-back stacked heptameric rings. They assist protein folding by undergoing large conformational changes that are controlled by ATP binding and hydrolysis. In the E. coli cell, only about 60 different proteins require GroEL for efficient folding. In the first part of the talk, I will describe work that was aimed at determining the properties that distinguish GroEL clients from non-clients. In the second part of the talk, I will describe new approaches for establishing allosteric mechanisms. Using these approaches, it was possible to show that the chaperonin GroEL from E. coli undergoes concerted intra-ring conformational changes whereas its eukaryotic homologue CCT/TRiC undergoes sequential intra-ring conformational changes. The impact of these different allosteric mechanisms on the folding functions of GroEL and CCT/TRiC will be discussed.
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