Identification of a novel mammalian endoplasmic reticulum-resident KDEL protein using an EST database motif search

Several endoplasmic reticulum (ER)-resident proteins contain a unique C-ter minal sequence (KDEL) which is required for the retention of these proteins in the ER. By searching a mouse EST database for records containing the nu cleotide sequence encoding the KDEL motif, we extracted cDNAs encoding puta tive novel ER-resident proteins in addition to all of the known ER proteins bearing the KDEL motif. Using the sequence information obtained by this da tabase search, we cloned the cDNA encoding a novel KDEL motif-bearing prote in, ER protein 58 (EP58), sharing no significant homology to any of the kno wn ER-resident proteins. Subcellular localization of EP58 in the ER was con firmed by cytoimmunofluorescence studies using epitope-tagged EP58. The EP5 8 gene was primarily expressed in embryo, placenta, and adult heart. Neithe r heat shock nor ER stress as tested here was sufficient to induce expressi on of the EP58 gene. A putative role of the N-terminal half of EP58 in prot ein-protein interaction is suggested by its similarity to the filamin rod d omain. Similarity of the EP58 sequence with bacterial and fungus proteins s uggests a possible role for EP58 in polysaccharide biosynthesis. (C) 2000 E lsevier Science B.V. All rights reserved.