SPECIFICITY OF THE ESCHERICHIA-COLI CHAPERONE DNAK (70-KDA HEAT-SHOCKPROTEIN) FOR HYDROPHOBIC AMINO-ACIDS

Molecular chaperones form a class of proteins that bind selectively to nascent, unfolded, misfolded, or aggregated polypeptides. This proper ty is the basis of their implication in many cellular processes such a s protein folding, protein targeting to membranes, or protein renatura tion after stress. It has been suggested that the recognition of non-n ative proteins by chaperones is mediated by their binding to exposed h ydrophobic areas, to the polypeptide backbone, or to specific secondar y structures. We show in the present study that DnaK, the 70-kDa chape rone of Escherichia coli specifically recognizes hydrophobic amino aci ds. The peptide-dependent ATPase activity of DnaK is specifically stim ulated 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 in side the hydrophobic core of native proteins and are exposed in non-na tive forms, their interaction with DnaK could be the basis of the spec ific interaction of the chaperone with non-native proteins in protein folding, protein targeting to membranes, or protein renaturation.