A Human Homologue Of The Yeast HDEL Receptor

RETENTION of resident proteins in the lumen of the endoplasmic reticulum is achieved in both yeast and animal cells by their continual retrieval from the cis-Golgi, or a pre-Golgi compartment1–3. Sorting of these proteins is dependent on a C-terminal tetrapeptide signal, usually Lys-Asp-Glu-Leu (KDEL in the single letter code) in animal cells, His-Asp-Glu-Leu (HDEL) in Sac-charomyces cerevisiae2,4,5. There is evidence that the ERD2 gene encodes the sorting receptor that recognizes HDEL in yeast6,7; its product is an integral membrane protein of relative molecular mass 26,000 (26K) that is not glycosylated. In contrast, Vaux et al.8 suggest that the mammalian KDEL receptor is a 72K gly-coprotein that they detected using an anti-idiotypic antibody approach. If this were so, it would indicate a surprising divergence of the retrieval machinery between yeast and animal cells. We report here that human cells express a protein similar in sequence, size and properties to the ERD2 product, and propose that this protein is the human KDEL receptor.