Specificity of the Escherichia coli chaperone DnaK (70-kDa heat shock protein) for hydrophobic amino acids.

Molecular chaperones form a class of proteins that bind selectively to nascent, unfolded, misfolded, or aggregated polypeptides. This property is the basis of their implication in many cellular processes such as protein folding, protein targeting to membranes, or protein renaturation after stress. It has been suggested that the recognition of non-native proteins by chaperones is mediated by their binding to exposed hydrophobic areas, to the polypeptide backbone, or to specific secondary structures. We show in the present study that DnaK, the 70-kDa chaperone of Escherichia coli specifically recognizes hydrophobic amino acids. The peptide-dependent ATPase activity of DnaK is specifically stimulated by Ile, Phe, Leu, and Val in a manner which is consistent with an interaction of these amino acids with the polypeptide binding site of DnaK. Two classes of amino acid binding site can be distinguished, one being specific for the aliphatic amino acids and the other for the aromatic amino acids. Since the hydrophobic amino acids are buried inside the hydrophobic core of native proteins and are exposed in non-native forms, their interaction with DnaK could be the basis of the specific interaction of the chaperone with non-native proteins in protein folding, protein targeting to membranes, or protein renaturation.