DISTINCT ACTIONS OF CIS AND TRANS ATP WITHIN THE DOUBLE-RING OF THE CHAPERONIN GROEL

The chaperonin GroEL is a double-ring structure with a central cavity in each ring that provides an environment for the efficient folding of proteins(1-3) when capped by the co-chaperone GroES in the presence o f adenine nucleotides(4-8). Productive folding of the substrate rhodan ese has been observed in cis ternary complexes, where GroES and polype ptide are bound to the same ring, formed with either ATP, ADP or non-h ydrolysable ATP analogues(2,9), suggesting that the specific requireme nt for ATP is confined to an action in the trans ring that evicts GroE S and polypeptide from the cis side(9). We show here, however, that fo r the folding of malate dehydrogenase and Rubisco there is also an abs olute requirement for ATP in the cis ring, as ADP and AMP-PNP are unab le to promote folding. We investigated the specific roles of binding a nd hydrolysis of ATP in the cis and trans rings using mutant forms of GroEL that bind ATP but are defective in its hydrolysis. Binding of AT P and GroES in cis initiated productive folding inside a highly stable GroEL-ATP-GroES complex. To discharge GroES and polypeptide, ATP hydr olysis in the cis ring was required to form a GroEL-ADP-GroES complex with decreased stability, priming the cis complex for release by ATP b inding (without hydrolysis) in the trans ring. These observations offe r an explanation of why GroEL functions as a double-ring complex.