InterPro domain: IPR015720

This group of proteins consists of TMP21 (also known as transmembrane emp24 domain-containing protein 10) and related proteins, which are members 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 [ 1 , 2 ].

p24 proteins are major membrane components of COPI- and COPII-coated vesicles and are implicated in cargo selectivity of ER to Golgi transport [ 3 , 4 ]. 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 [ 5 ]. One subfamily comprises yeast Emp24p and mammalian p24A. Another subfamily comprises yeast Erv25p and mammalian Tmp21, and the third subfamily comprises mammalian gp25L proteins.

1. p24 proteins, intracellular trafficking, and behavior: Drosophila melanogaster provides insights and opportunities. Biol. Cell 96, 271-8
2. Biosynthetic protein transport through the early secretory pathway. Histochem. Cell Biol. 109, 477-86
3. gp25L/emp24/p24 protein family members of the cis-Golgi network bind both COP I and II coatomer. J. Cell Biol. 140, 751-65
4. A major transmembrane protein of Golgi-derived COPI-coated vesicles involved in coatomer binding. J. Cell Biol. 135, 1239-48
5. Tmp21 and p24A, two type I proteins enriched in pancreatic microsomal membranes, are members of a protein family involved in vesicular trafficking. J. Biol. Chem. 271, 17183-9