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Endopeptidase Clp
Protein family From Wikipedia, the free encyclopedia
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Endopeptidase Clp (EC 3.4.21.92, endopeptidase Ti, caseinolytic protease, protease Ti, ATP-dependent Clp protease, ClpP, Clp protease).[1][2][3][4] This enzyme catalyses the following chemical reaction
- Hydrolysis of proteins to small peptides in the presence of ATP and Mg2+.
This bacterial enzyme contains subunits of two types, ClpP, with peptidase activity, and the protein ClpA, with AAA+ ATPase activity. ClpP and ClpA are not evolutionarily related.
A fully assembled Clp protease complex has a barrel-shaped structure in which two stacked heptameric ring of proteolytic subunits (ClpP or ClpQ) are either sandwiched between two rings or single-caped by one ring of hexameric ATPase-active chaperon subunits (ClpA, ClpC, ClpE, ClpX, ClpY, or others).[5]
ClpXP is presented in almost all bacteria while ClpA is found in the Gram-negative bacteria, ClpC in Gram-Positive bacteria and cyanobacteria. ClpAP, ClpXP and ClpYQ coexist in E. coli while only ClpXP complex in present in humans as mitochondrial enzymes.[5] ClpYQ is another name for the HslVU complex, a heat shock protein complex thought to resemble the hypothetical ancestor of the proteasome.[6]
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The Hsp100 family of eukaryotic heat shock proteins is homologous to the ATPase-active chaperon subunits found in the Clp complex; as such the entire group is often referred to as the HSP100/Clp family. The family is usually broken into two parts, one being the ClpA/B family with two ATPase domains, and the other being ClpX and friends with only one such domain.[7] ClpA through E is put into the first group along with Hsp78/104, and ClpX and HSIU is put into the second group.[8]
Many of the proteins are not associated with a protease and have functions other than proteolysis. ClpB (human CLPB "Hsp78", yeast Hsp104) break up insoluble protein aggregates in conjunction with DnaK/Hsp70. They are thought to function by threading client proteins through a small 20 Å (2 nm) pore, thereby giving each client protein a second chance to fold.[8][9][10] A member of the ClpA/B family termed ClpV is used in the bacterial T6SS.[11]
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