9.B.188.1.9
Transmembrane emp24 domain-containing protein 9 of 235 aas and 2 TMSs, N- and C-terminal, TMED9. The secretory pathway is an intracellular highway for the vesicular transport of newly synthesized proteins that span the ER, Golgi, lysosomes and cell surface. A variety of cargo receptors, chaperones, and quality control proteins maintain the smooth flow of cargo along this route. Among these is vesicular transport protein TMED9, which belongs to the p24/transmembrane emp24 domain (TMED) family of proteins. It is expressed across vertebrate species (Roberts and Satpute-Krishnan 2022). The TMED family consists of structurally-related type I transmembrane proteins with a luminal N-terminal Golgi-dynamics domain, a luminal coiled-coil domain, a transmembrane domain and a short cytosolic C-terminal tail that binds COPI and COPII coat proteins. TMED9, like other members of the TMED family, was first identified as an abundant constituent of the COPI and COPII coated vesicles that mediate traffic between the ER and the Golgi. TMED9 is typically purified in hetero-oligomers together with TMED family members, suggesting that it may function as part of a complex. TMED family members play various roles in secretory pathway homeostasis including secreted protein processing, quality control and degradation of misfolded proteins, and post-Golgi trafficking. In particular, TMED9 has been implicated in autophagy, lysosomal sorting, viral replication and cancer (Roberts and Satpute-Krishnan 2022).