InterPro domain: IPR004342

The EXS domain is named after ERD1/XPR1/SYG1 and proteins containing this motif include the C-terminal of the SYG1 G-protein associated signal transduction protein from Saccharomyces cerevisiae, and sequences that are thought to be Murine leukemia virus (MLV) receptors (XPR1. The N-terminal of these proteins often have an SPX domain ( IPR004331 ) [ 1 ].

While the N-terminal is thought to be involved in signal transduction, the role of the C-terminal is not known. This region of similarity contains several predicted transmembrane helices. This family also includes the ERD1 (ERD: ER retention defective) S. cerevisiae proteins. ERD1 proteins are involved in the localization of endogenous endoplasmic reticulum (ER) proteins. Erd1 null mutants secrete such proteins even though they possess the C-terminal HDEL ER lumen localization label sequence. In addition, null mutants also exhibit defects in the Golgi-dependent processing of several glycoproteins, which led to the suggestion that the sorting of luminal ER proteins actually occurs in the Golgi, with subsequent return of these proteins to the ER via `salvage' vesicles [ 2 ].

1. A human cell-surface receptor for xenotropic and polytropic murine leukemia viruses: possible role in G protein-coupled signal transduction. Proc. Natl. Acad. Sci. U.S.A. 96, 1385-90
2. ERD1, a yeast gene required for the retention of luminal endoplasmic reticulum proteins, affects glycoprotein processing in the Golgi apparatus. EMBO J. 9, 623-30