CALUMENIN, A CA2-BINDING PROTEIN RETAINED IN THE ENDOPLASMIC-RETICULUM WITH A NOVEL CARBOXYL-TERMINAL SEQUENCE, HDEF()

We have identified and characterized a cDNA encoding a novel Ca2+-bind ing protein named calumenin from mouse heart by the signal sequence tr ap method, The deduced amino acid sequence (315 residues) of calumenin contains an amino-terminal signal sequence and sis Ca2+-binding (EF-h and) motifs and shows homology with reticulocalbin, Erc-55, and Cab45. These proteins seem to form a new subset of the EF-hand protein famil y expressed in the lumen of the endoplasmic reticulum (ER) and Golgi a pparatus. Purified calumenin had Ca2+-binding ability. The carboxyl-te rminal tetrapeptide His-Asp-Glu-Phe was shown to be responsible far re tention of calumenin in ER by the retention assay, immunostaining with a confocal laser microscope, and the deglycosylation assay, This is t he first report indicating that the Phe residue is included in the ER retention signal, Calumenin is expressed most strongly in heart of adu lt and 18.5-day embryos. The calumenin gene (Calu) was mapped at the p roximal portion of mouse chromosome 7.