GroEL binds artificial proteins with random sequences

Chaperonin GroEL from Escherichia coli binds to the non-native states of ma ny unrelated proteins, and GroEL-recognizable structural features have been argued. As model substrate proteins of GroEL, we used seven artificial pro teins (138 similar to 141 residues), each of which has a unique but randoml y chosen amino acid sequence and no propensity to fold into a certain struc ture. Two of them were water-soluble, and the rest were soluble in 3 M urea . The soluble ones interacted with GroEL in a manner similar to that of a n atural substrate; they stimulated the ATPase cycle of GroEL and GroEL/ GroE S and inhibited GroEL-assisted folding of other protein. All seven artifici al proteins were able to bind to GroEL, The results suggest that the second ary structure as well as the specific sequence motif of the substrate prote ins are not necessary to be recognized by GroEL.