COPII–cargo interactions direct protein sorting into ER-derived transport vesicles

Abstract

Vesicles coated with coat protein complex II (COPII) selectively transport molecules (cargo) and vesicle fusion proteins from the endoplasmic reticulum (ER) to the Golgi complex. We have investigated the role of coat proteins in cargo selection and recruitment. We isolated integral membrane and soluble cargo proteins destined for transport from the ER in complexes formed in the presence of Sar1 and Sec23/24, a subset of the COPII components, and GTP or GMP-PNP. Vesicle fusion proteins of the vSNARE family and Emp24, a member of a putative cargo carrier family, were also found in COPII complexes. The inclusion of amino-acid permease molecules into the complex depended on the presence of Shr3, a protein required for the permease to leave the ER. Resident ER proteins Sec61, BiP (Kar2) and Shr3 were not included in the complexes, indicating that the COPII components bound specifically to vesicle cargo. COPII-cargo complexes and putative cargo adaptor-cargo complexes were also isolated from COPII vesicles. Our results indicate that cargo packaging signals and soluble cargo adaptors are recognized by a recruitment complex comprising Sar1-GTP and Sec23/24.

Clustering of Peptide-Loaded MHC Class I Molecules for Endoplasmic Reticulum Export Imaged by Fluorescence Resonance Energy Transfer

“…The specific clustering of peptide-loaded MHC that we observed supports the second ER export mechanism. It is generally believed that transmembrane proteins are selectively recruited into ER exit sites by interactions of their cytoplasmic tails with the coat protein complex (COPII) coat (30,31). HLA-A2 lacks either of the putative signals for ER export, the di-phenylalanine (FF), or the diacidic (DϫE) motifs (32)(33)(34)(35)(36).…”

Mea6 controls VLDL transport through the coordinated regulation of COPII assembly

“…Sar1 binds to the ER membrane in its GTP-bound state and recruits the Sec23/24 heterodi-mer that forms the inner coat, which in turn recruits the outer coat proteins Sec13 and 31 to form the complex [14,15]. Sar1B mutations are associated with chylomicron retention disease and hepatic steatosis, likely resulting from retention of lipoproteins in the ER [17][18][19].…”

“…Vesicular trafficking factors such as coat protein complex II (COPII), which is composed of small GTPase (Sar1) and COPII coat proteins Sec23, 24, 13 and 31, play a crucial role in transporting ER cargoes to the Golgi apparatus [14][15][16]. Sar1 binds to the ER membrane in its GTP-bound state and recruits the Sec23/24 heterodi-mer that forms the inner coat, which in turn recruits the outer coat proteins Sec13 and 31 to form the complex [14,15].…”

Les gènes et les protéines qui contrôlent la voie de sécrétion

“…Meta Kuehn, un post-doc du labo, a détecté une interaction de la perméase de la membrane plasmique et des protéines SNARE mais il n'y avait pas d'interaction des protéines luminales résidentes du RE avec les sousunités COPII pendant une incubation des membranes en présence d'un analogue non hydrolysable du GTP (Kuehn et al, 1998). Le laboratoire de Bill Balch a observé une interaction analogue du Sec23/24 de mammifère avec un intermédiaire de transit de la protéine G du VSV et découvert que l'interaction dépend d'une séquence de tri C-terminale, ..DxE., dans la protéine G (Nishimura & Balch, 1997).…”