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Ubiquitin regulatory domain X (UBX) 2 found in UBX domain protein 9 (UBXN9, UBXD9, or ASPSCR1) and similar proteins UBXN9, also termed tether containing UBX domain for GLUT4 (TUG), or alveolar soft part sarcoma chromosomal region candidate gene 1 protein (ASPSCR1), or alveolar soft part sarcoma locus (ASPL), or renal papillary cell carcinoma protein 17 (RCC17), belongs to the UBXD family of proteins that contains two ubiquitin regulatory domains 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. In addition, UBXN9 contains an N-terminal ubiquitin-like (Ubl) domain. UBXN9 functions as a cofactor of p97 (also known as VCP or Cdc48), which is a homohexameric AAA ATPase (ATPase associated with a variety of activities) involved in a variety of functions ranging from cell-cycle regulation to membrane fusion and protein degradation. However, high-affinity interacting protein ASPL efficiently promotes p97 hexamer disassembly, resulting in the formation of stable p97:ASPL heterotetramers; the extended UBX domain (eUBX) in ASPL is critical for p97 hexamer disassembly and facilitates the assembly of p97:ASPL heterotetramers.UBXN9 is involved in insulin-stimulated redistribution of the glucose transporter GLUT4, assembly of the Golgi apparatus. In addition to GLUT4, UBXN9 also controls vesicle translocation by interacting with insulin-regulated aminopeptidase (IRAP), a transmembrane aminopeptidase. UBXN9 and its budding yeast ortholog, Ubx4p, are multifunctional proteins that share some, but not all functions. Yeast Ubx4p is important for endoplasmic reticulum-associated protein degradation (ERAD) but UBXN9 appears not to share this function. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",