Poly-L-lysine enhances the protein disaggregation activity of ClpB

The Hsp100 protein ClpB is a member of the AAA+ protein family that mediates the solubilization of aggregated proteins in cooperation with the DnaK chaperone system. Unstructured polypeptides such as casein or poly-L-lysine have been shown to stimulate the ATPase activity of ClpB and thus may both act as substrates. Here we compared the effects of alpha-casein and poly-L-lysine on the ATPase and chaperone activities of ClpB. alpha-Casein stimulated ATP hydrolysis by both AAA domains of ClpB and inhibited the ClpB-dependent solubilization of aggregated proteins if present in excess. In contrast, poly-L-lysine stimulated exclusively the ATPase activity of the second AAA domain and increased the disaggregation activity of ClpB. Thus poly-L-lysine does not act as substrate, but rather represents an effector molecule, which enhances the chaperone activity of ClpB.