Reticulocalbin, a novel endoplasmic reticulum resident Ca(2+)-binding protein with multiple EF-hand motifs and a carboxyl-terminal HDEL sequence.
A novel Ca(2+)-binding protein, tentatively designated reticulocalbin, has been identified and characterized. Reticulocalbin is a luminal protein of the endoplasmic reticulum with an M(r) of 44,000 as revealed by biochemical analysis and immunofluorescence staining. The cDNA of reticulocalbin encodes a protein of 325 amino acids with an amino-terminal signal sequence of 20 amino acids. The protein has six repeats of a domain containing the high affinity Ca(2+)-binding motif, the EF-hand. Although oxygen-containing amino acids important for the positioning of Ca2+ are conserved in all six domains, the conserved glycine residues in the central portion of the EF-hand motif are absent in three of them. Calcium blots showed that recombinant reticulocalbin expressed in bacterial cells binds Ca2+. The protein has the sequence His-Asp-Glu-Leu (HDEL) at its carboxyl terminus. This is similar to the Lys-Asp-Glu-Leu sequence, which serves as a signal to retain the resident proteins in the endoplasmic reticulum of animal cells. A mutant protein lacking the HDEL sequence produced by in vitro mutagenesis has been shown to be secreted into medium in transient expression assays.
Ozawa
M
M
Department of Biochemistry, Faculty of Medicine, Kagoshima University, Japan.
Muramatsu
T
T
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D064026:Calbindins; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D003001:Cloning, Molecular; D004273:DNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005455:Fluorescent Antibody Technique; D051379:Mice; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000032:analysis / Q000378:metabolism; D015183:Restriction Mapping; D064030:S100 Calcium Binding Protein G / Q000235:genetics; D013724:Teratoma; D014407:Tumor Cells, Cultured
D064026:Calbindins; D002135:Calcium-Binding Proteins; D004273:DNA, Neoplasm; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D064030:S100 Calcium Binding Protein G; C078865:reticulocalbin