dnaK

DnaK is a molecular chaperone of the bacterial Hsp70 family. Encoded by the dnaK gene, it is a central component of the cellular protein quality control system, especially during stress such as heat shock. DnaK assists the folding, stabilization, and rescue of nascent or denatured polypeptides and prevents aggregation.

Its structure features an N-terminal ATPase (nucleotide-binding) domain and a C-terminal substrate-binding domain with a lid. DnaK operates in an ATP-dependent cycle: ATP binding lowers substrate affinity, whereas hydrolysis induced by the J-domain protein DnaJ increases affinity; GrpE promotes nucleotide exchange to release substrates.

In bacteria, DnaK functions with co-chaperones DnaJ and GrpE, forming the DnaK–DnaJ–GrpE system that folds many newly synthesized proteins and rescues stress-denatured ones. The system also supports protein translocation and assembly of complexes in some species, illustrating the diverse roles of DnaK in proteome maintenance.

Conservation and significance: DnaK is widespread in bacteria and has homologs in organelles such as mitochondria and chloroplasts. Its expression is upregulated by heat shock (often via the sigma factor RpoH). Because of its essential role in protein quality control, DnaK is frequently used as a model for Hsp70 function and is implicated in pathogen survival in some species.