These proteins are related to glycoprotein 25L, or gp25L, which is a member of the p24 family. The p24 family is a widely conserved family of transmembrane proteins that plays a functional role in the initiation of assembly of COPI (Coat protein I) coated vesicles. COPI coated vesicles are involved in protein transport within the early secretory pathway [, ].p24 proteins are major membrane components of COPI- and COPII-coated vesicles and are implicated in cargo selectivity of ER to Golgi transport [, ]. Multiple members of the p24 family are found in all eukaryotes, from yeast to mammals. Members of the p24 family are type I membrane proteins with a signal peptide at the amino terminus, a lumenal coiled-coil (extracytosolic) domain, a single transmembrane domain with conserved amino acids, and a short cytoplasmic tail. They may be grouped into at least three subfamilies based on primary sequence []. One subfamily comprises yeast Emp24p and mammalian p24A. Another subfamily comprises yeast Erv25p and mammalian Tmp21, and the third subfamily comprises mammalian gp25L proteins.
