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Ubiquitin regulatory domain X (UBX) found in UBX domain protein 7 (UBXN7) and similar proteins UBXN7, also termed UBX domain-containing protein 7 (UBXD7), belongs to the UBXD family of proteins that contains the ubiquitin regulatory domain X (UBX) with a beta-grasp ubiquitin-like fold, but without the C-terminal double glycine motif. UBX domain is typically located at the carboxyl terminus of proteins, and participates broadly in the regulation of protein degradation. UBXN7 functions as a ubiquitin-binding adaptor that mediates the interaction between the AAA+ ATPase p97 (also known as VCP or Cdc48) and the transcription factor HIF1-alpha. It binds only to the active, NEDD8- or Rub1-modified form of cullins. In addition to having a UBX domain, UBXD7 contains a ubiquitin-associated (UBA), ubiquitin-associating (UAS), and ubiquitin-interacting motif (UIM) domains. Either UBA or UIM could serve as a docking site for neddylated-cullins. UBA domain is required for binding ubiquitylated-protein substrates, while the UIM motif is responsible for the binding to cullin RING ligases (CRLs), and the UBX domain is essential for p97 binding.
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