High impact information on EMP24

• Members of the yeast p24 family, including Emp24p and Erv25p, form a heteromeric complex required for the efficient transport of selected proteins from the endoplasmic reticulum (ER) to the Golgi apparatus [1].
• We show that Emp24p is directly required for efficient packaging of a lumenal cargo protein, Gas1p, into ER-derived vesicles [1].
• Gap1p, which was not affected by emp24 mutation, was not cross-linked [1].
• These results suggest that the Emp24 complex acts as a cargo receptor in vesicle biogenesis from the ER [1].
• Abstract. Five mammalian members of the gp25L/ emp24/p24 family have been identified as major constituents of the cis-Golgi network of rat liver and HeLa cells [2].

Biological context of EMP24

• These phenotypes are similar to those caused by deletion of EMP24 or ERV25, two previously identified genes that encode related p24 proteins [3].
• Logjam encodes a predicted EMP24/GP25 protein that is required for Drosophila oviposition behavior [4].
• Emp24p is a type I transmembrane protein that is involved in secretory protein transport from the endoplasmic reticulum (ER) to the Golgi complex [5].
• Oligomerization and protease digestion studies of invertase suggest that the selective transport phenotype observed in the emp24 delta mutant is not due to a defect in protein folding or oligomerization [5].
• A yeast mutant that lacks Emp24p (emp24 delta) is viable, but periplasmic invertase and the glycosylphosphatidyl-inositol-anchored plasma membrane protein Gas1p are delivered to the Golgi apparatus with reduced kinetics, whereas transport of alpha-factor, acid phosphatase and two vacuolar proteins is unaffected [5].

Anatomical context of EMP24

• Distinct roles for the cytoplasmic tail sequences of Emp24p and Erv25p in transport between the endoplasmic reticulum and Golgi complex [6].
• In an H. polymorpha wild-type background, deletion of EMP24 and ERP3 resulted in a strong reduction of organelle number in conjunction with an increase in the size of individual peroxisomes [7].
• This process was impaired upon deletion of EMP24 and ERP3, genes that encode p24 proteins. p24 Proteins are components of coated vesicles that mediate trafficking between the endoplasmic reticulum and Golgi apparatus [7].
• The absence of Emp24p, a component of ER-derived COPII-coated vesicles, causes a defect in transport of selected proteins to the Golgi [5].
• We propose that Emp24p is involved in the sorting and/or concentration of a subset of secretory proteins into ER-derived transport vesicles [5].

Associations of EMP24 with chemical compounds

• COPI subunits also bound to these Emp24p and Erv25p peptides; however, the Erv25p tail sequence, which contains a dilysine motif, bound COPI more efficiently [6].
• We used this assay to investigate how targeting [v-SNARE, vesicle-soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein receptor], putative adapter (e.g., Emp24p), and cargo molecules are captured into ER-derived COPII vesicles [8].

Other interactions of EMP24

• Genetic and biochemical studies demonstrate that Erp1p and Erp2p function in a heteromeric complex with Emp24p and Erv25p [3].
• The BST1 and BST2/EMP24 genes code for integral membrane proteins that reside predominantly in the ER [9].
• More Sar1p (the GTP-binding protein that initiates vesicles budding) is needed to package the membrane-associated v-SNAREs and Emp24p than is needed to package the soluble secretory protein glycosylated pro-alpha-factor (gp alphaF) [8].
• Finally, we show that membranes prepared from strains with mutations in the SEC16 gene are more defective for the packaging of v-SNARE molecules and Emp24p than they are for the packaging of gp alphaF [8].
• As Yos9 is not a component of the Emp24 complex, it may act as a novel escort factor for GPI-anchored proteins in ER-Golgi transport in yeast and possibly in mammals [10].

References