SEQUENCE SIMILARITY OF CALRETICULIN WITH A CA-2+-BINDING PROTEIN THAT COPURIFIES WITH AN INS(1,4,5)P3-SENSITIVE CA-2+ STORE IN HL-60 CELLS

HL-60 cells possess a 60 kDa Ca2+-binding protein that is contained in a discrete subcellular compartment, referred to as calciosomes. Subcellular fractionation studies have suggested that, in HL-60 cells, this intracellular compartment is an Ins(1,4,5)P3-sensitive Ca2+ store. In order to investigate the structural relationship of the 60 kDa Ca2+-binding protein of HL-60 cells to other Ca2+-binding proteins, we have purified the protein by ammonium sulphate extraction, acid precipitation, and DEAE-cellulose and phenyl-Sepharose column chromatography. The N-terminal sequence of the protein shows 93% identity with rabbit muscle calreticulin, a recently cloned sarcoplasmic reticulum Ca2+-binding protein. No amino acid sequence similarity with calsequestrin was found, although the purified protein cross-reacted with anti-calsequestrin antibodies. The calreticulin-related protein of HL-60 cells might play a role as an intravesicular Ca2+-binding protein of an Ins(1,4,5)P3-sensitive Ca2+ store.