GrpE is a so-called co-chaperone because it is known to assist the DnaK (Hsp70) protein to effectively carry out DnaK-dependent chaperone activity (i.e. protein folding, protein transport, disaggregation of heat inactivated proteins, activation of mutant protein). GrpE acts as a nucleotide exchange factor for DnaK, the main Hsp70 protein in bacteria, accelerating ADP/ATP exchange by several orders of magnitude. Unfolded proteins bind initially to dnaJ; upon interaction with the dnaJ-bound protein, dnaK hydrolyzes its bound ATP, resulting in the formation of a stable complex. GrpE releases ADP from dnaK; ATP binding to dnaK triggers the release of the substrate protein, thus completing the reaction cycle. GrpE may also function as a thermosensor. GrpE is a homodimer, each subunit containing three structural domains: a N-terminal unordered segment, two long coils and a C-terminal globular domain formed by a four-helix bundle, and a beta-subdomain.