GROES AND THE CHAPERONIN-ASSISTED PROTEIN-FOLDING CYCLE - GROES HAS NO AFFINITY FOR NUCLEOTIDES

The E. coli chaperonin proteins, GroEL and GroES, assist in folding ne wly synthesized proteins, GroES is necessary for GroEL-assisted foldin g under conditions where the substrate protein cannot spontaneously fo ld, On the basis of photolabelling of GroES with 8-azido-ATP, a role f or nucleotide binding to GroES in chaperonin function was suggested [M artin, et al., Nature, 366 (1993) 279-282], We confirm the photolabell ing of GroES,vith 8-azido-ATP. However, other proteins not known to co ntain nucleotide binding sites also became photolabeled suggesting tha t labeling is non-specific, Using rigorous physical methods, isotherma l calorimetry and equilibrium binding, no interaction between GroES an d nucleotides could be detected, We conclude that GroES has no nucleot ide binding site.