Identification of two isoforms of the vesicle-membrane fusion protein SNAP-23 in human neutrophils and HL-60 cells

We have identified and clotted two isoforms of SNAP-23 in human neutrophils and human promyelocytic HL-60 cells. SNAP-23A which is similar to the recently cloned SNAP-23, and a novel isoform, termed SNAP-23B. SNAP-23B results from a deletion of 159 bp of the SNAP-23A cDNA, encoding a protein of approximately 17.8 kDa. SNAP-23B is identical to SNAP-23A, but lacks fifty-three amino acid residues, from 90 to 142. This region of SNAP-23A has a target sequence for posttranslational fatty acid acylation, suggesting that the two isoforms can differ in their capacity to interact with membranes. The level of SNAP-23 mRNA is increased during HL-60 neutrophil differentiation. These findings demonstrate the existence of two SNAP-23 proteins in human neutrophils; and therefore, these cells have all the proteins needed to carry out the exocytic process. (C) 1997 Academic Press.