Interaction of DnaK with native proteins and membrane proteins correlates with their accessible hydrophobicity

Molecular chaperones are involved in protein folding, protein targeting to membranes, and protein renaturation after stress. They interact specificall y with hydrophobic sequences that are exposed in unfolded proteins, and bur ied in native proteins. We have studied the interaction of DnaK with native water-soluble proteins and membrane proteins. DnaK-native protein interact ions are characterized by dissociation constants between 1 and 50 mu M (com pared with 0.01-1 mu M for unfolded proteins). This affinity is within the range of most intracellular protein concentrations, suggesting that DnaK in teracts with a greater number of native proteins than previously suspected. We found a correlation between the affinity of native proteins for DnaK an d their affinity for hydrophobic-interaction chromatography adsorbents, sug gesting that DnaK interacts with exposed hydrophobic groups in native prote ins. The interaction between DnaK and membrane proteins is characterized by DnaK's high affinity for detergent-solubilized membrane proteins, and its lower affinity for membrane proteins inserted in lipid bilayers, suggesting that the chaperone can interact with the hydrophobic sequences of the form er, while it cannot penetrate the hydrophobic core of lipid bilayers. Thus, the specificity of DnaK for hydrophobic sequences is involved in its inter action with not only unfolded proteins, but also native water-soluble prote ins and membrane proteins. All proteins interact with DnaK according to the ir exposed hydrophobicity. (C) 1999 Elsevier Science B.V. All rights reserv ed.