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Mol Biol Cell. 2003 Sep;14(9):3753-66. Epub 2003 May 18.

Endoplasmic reticulum export of glycosyltransferases depends on interaction of a cytoplasmic dibasic motif with Sar1.

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1
Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 Córdoba, Argentina.

Abstract

Membrane proteins exit the endoplasmic reticulum (ER) in COPII-transport vesicles. ER export is a selective process in which transport signals present in the cytoplasmic tail (CT) of cargo membrane proteins must be recognized by coatomer proteins for incorporation in COPII vesicles. Two classes of ER export signals have been described for type I membrane proteins, the diacidic and the dihydrophobic motifs. Both motifs participate in the Sar1-dependent binding of Sec23p-Sec24p complex to the CTs during early steps of cargo selection. However, information concerning the amino acids in the CTs that interact with Sar1 is lacking. Herein, we describe a third class of ER export motif, [RK](X)[RK], at the CT of Golgi resident glycosyltransferases that is required for these type II membrane proteins to exit the ER. The dibasic motif is located proximal to the transmembrane border, and experiments of cross-linking in microsomal membranes and of binding to immobilized peptides showed that it directly interacts with the COPII component Sar1. Sar1GTP-bound to immobilized peptides binds Sec23p. Collectively, the present data suggest that interaction of the dibasic motif with Sar1 participates in early steps of selection of Golgi resident glycosyltransferases for transport in COPII vesicles.

PMID:
12972562
PMCID:
PMC196565
DOI:
10.1091/mbc.E03-02-0101
[Indexed for MEDLINE]
Free PMC Article
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