Abstract

ClpB is a Clp/Hsp100 molecular chaperone belonging to the AAA+ (ATPases Associated with various cellular Activities) superfamily. Following severe stress, ClpB promotes cell survival by disaggregating and reactivating damaged proteins. ClpB forms a hexamer as its active conformation, which is stabilized in the presence of ATP and substrate. ClpB uses the energy of ATP hydrolysis to unfold and translocate substrate polypeptides through the central pore of the hexamer. To disaggregate insoluble aggregates, ClpB functions with the DnaK chaperone system although it can act alone on specific substrates. We are interested in determining how the substrate translocation process is linked to substrate binding in the ClpB hexamer and how the DnaK system may influence this process. To this end, we mutated ClpB in regions known to interact with substrate, including highly conserved tyrosines located in loops in the central channel of the hexamer. Our data from protein remodeling experiments suggest that each ClpB pore tyrosine acts independently on substrates requiring DnaK, but more cooperatively when ClpB works alone. These data indicate that DnaK influences the function of the ClpB pore residues, possibly by stabilizing ClpB‐substrate interactions.

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