InterPro domain: IPR004487

ClpX is a member of the HSP (heat-shock protein) 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 [ 1 ]. It functions as an ATP-depedent [ 2 ] molecular chaperone and is the regulatory subunit of the ClpXP protease [ 2 ].

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 [ 3 ].

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 [ 4 ].

1. Enzymatic and structural similarities between the Escherichia coli ATP-dependent proteases, ClpXP and ClpAP. J. Biol. Chem. 273, 12476-81
2. Purification, crystallization and preliminary X-ray studies of ClpX from Helicobacter pylori. Acta Crystallogr. D Biol. Crystallogr. 59, 1642-4
3. Proteomic discovery of cellular substrates of the ClpXP protease reveals five classes of ClpX-recognition signals. Mol. Cell 11, 671-83
4. The N-terminal zinc binding domain of ClpX is a dimerization domain that modulates the chaperone function. J. Biol. Chem. 278, 48981-90