Characterization of the N-terminal repeat domain of Escherichia coli ClpA - A class I Clp/HSP100 ATPase

The ClpA, ClpB, and ClpC subfamilies of the Clp/HSP100 ATPases contain a co nserved N-terminal region of similar to 150 residues that consists of two a pproximate sequence repeats. This sequence from the Escherichia coli ClpA e nzyme is shown to encode an independent structural domain (the R domain) th at is monomeric and similar to 40% alpha -helical. A ClpA fragment lacking the R domain showed ATP-dependent oligomerization, protein-stimulated ATPas e activity, and the ability to complex with the ClpP peptidase and mediate degradation of peptide acid protein substrates, including casein and ssrA-t agged proteins. Compared with the activities of the wild-type ClpA, however , those of the ClpA fragment missing the R domain were reduced. These resul ts indicate that the R domain is not required for the basic recognition, un folding, and translocation functions that allow ClpA-ClpP to degrade some p rotein substrates, but they suggest that it may play a role in modulating t hese activities.