Caseinolytic Peptidase X (CLPX)

ClpX is a member of the HSP 100 family. Gel filtration and electron microscopy showed that ClpX subunits associate to form a six-membered ring that is stabilised by binding of ATP or nonhydrolysable analogs of ATP. It functions as an ATP-depedent molecular chaperone and is the regulatory subunit of the ClpXP protease.ClpXP is involved in DNA damage repair, stationary-phase gene expression, and ssrA-mediated protein quality control. To date more than 50 proteins include transcription factors, metabolic enzymes, and proteins involved in the starvation and oxidative stress responses have been identified as substrates. The N-terminal domain of ClpX is a C4-type zinc binding domain (ZBD) involved in substrate recognition. ZBD forms a very stable dimer that is essential for promoting the degradation of some typical ClpXP substrates such as lO and MuA.