FOLDING INTERMEDIATES OF BETA-LACTAMASE RECOGNIZED BY GROEL

beta-Lactamase, from which the disulfide bond was removed by two Cys-- >Ala mutations, forms stable complexes with GroEL only during the firs t 30 s of folding, while wild-type beta-lactamase forms no stable comp lex under these conditions, The 3-phasic kinetics of folding are very similar between wild-type and mutant, After 4 s, Trp-210 is already ju xtaposed to the disulfide bond, but proline cis-trans isomerization ha s not yet taken place and almost no enzymatic activity is observed. Th is shows that GroEL is unable to bind late folding intermediates and a lso discriminates between the degree of unfolding possible in wild-typ e disulfide-containing beta-lactamase and the Cys-Ala mutant.