HOW GROES REGULATES BINDING OF NONNATIVE PROTEIN TO GROEL

At present, it is still enigmatic how the reaction cycle by which the Escherichia coli GroE chaperones mediate protein folding in the cell i s coordinated with respect to the sequential order of binding and rele ase of GroES, nucleotide, and nonnative protein. It is generally assum ed that the asymmetric GroEL.GroES complex is the acceptor state for s ubstrate protein, Nevertheless, this species is poorly understood in i ts binding characteristics for nucleotide and nonnative protein, We sh ow here that this species has a high affinity binding site for nonnati ve protein. In addition to this, binding of nucleotide to one GroEL ri ng is strongly favored by GroES binding to the other ring, However, th e slow rate of release of substrate protein from the unproductive tran s-position kinetically favors the binding of a second GroES, thereby f orming a symmetric GroEL(14).(GroES(7))(2) complex and simultaneously ensuring that substrate protein is sequestered in a position underneat h GroES. Our results demonstrate that the intrinsic binding characteri stics of the trans-bullet complex determine the sequence of events dur ing the reaction cycle.