ubp

Small Glutamine-Rich Tetratricopeptide Repeat-Containing Protein α (SGTA) is an ubiquitously expressed protein which belongs to the SGT Family. SGTA contains three TPR Protein-Protein Interaction Duplicates. SGTA is a co-chaperone that binds directly to HSC70 and HSP70 and regulates their ATPase activity. SGTA is capable of interacting with the major nonstructural protein of Parvovirus H-1 and 70-kDa heat shock cognate protein. It interacts with NS1 from Parvovirus H-1, with Vpu and Gag from HIV-1. It also interacts with SARS-CoV Accessory Protein 7a, DNAJC5 and DNAJC5B. However, its function is not known. Since this transcript is expressed ubiquitously in various tissues, SGTA may serve a housekeeping function.

Ubiquitin carboxyl-terminal hydrolase 5, also known as Deubiquitinating enzyme 5, Isopeptidase T, Ubiquitin thiolesterase 5, Ubiquitin-specific-processing protease 5, ISOT and USP5, is a member of the peptidase C19 family. USP5 contains 2 UBA domains and one UBP-type zinc finger. The UBP-type zinc finger domain interacts selectively with an unmodified C-terminus of the proximal ubiquitin. Both UBA domains are involved in polyubiquitin recognition. The UBP-type zinc finger domain crystallizes as a dimer linked by a disulfide bond between the Cys-195 residues of both molecules, but there is no evidence that the full-length USP5 exists as a dimer. USP5 cleaves linear and branched multiubiquitin polymers with a marked preference for branched polymers. USP5 is involved in unanchored 'Lys-48'-linked polyubiquitin disassembly. It binds linear and 'Lys-63'-linked polyubiquitin with a lower affinity. Knock-down of USP5 causes the accumulation of p53 TP53 and an increase in p53 TP53 transcriptional activity because the unanchored polyubiquitin that accumulates is able to compete with ubiquitinated p53 TP53 but not with MDM2 for proteasomal recognition.