RELEASE OF BOTH NATIVE AND NONNATIVE PROTEINS FROM A CIS-ONLY GROEL TERNARY COMPLEX

PROTEIN folding by the double-ring chaperonin GroEL is initiated in ct s ternary complexes, in which polypeptide is sequestered in the centra l channel of a GroEL ring, capped by the co-chaperonin GroES(1-3), The cis ternary complex is dissociated (half-life of similar to 15 s) by trans-sided ATP hydrolysis, which triggers release of GroES(4-6). For the substrate protein rhodanese, only similar to 15% of cis-localized molecules attain their native form before hydrolysis(2,7). A major que stion concerning the GroEL mechanism is whether both native and non-na tive forms are released from the cis complex, Here we address this que stion using a 'cis-only' mixed-ring GroEL complex that binds polypepti de and GroES on only one of its two rings, This complex mediates refol ding of rhodanese but, as with wild-type GroEL, renaturation is quench ed by addition of mutant GroEL 'traps', which bind but do not release polypeptide substrate(7,8), This indicates that nonnative forms are re leased from the cis complex, Quenching of refolding by traps was also observed under physiological conditions, both in undiluted Xenopus ooc yte extract and in intact oocytes, We conclude that release of non-nat ive forms from GroEL in vivo allows a kinetic partitioning among vario us chaperones and proteolytic components, which determines both the co nformation and lifetime of a protein.