Peptidase Inhibitor 15 (PI15)

PI15 encodes a trypsin inhibitor. The protein shares similarity to insect venom allergens, mammalian testis-specific proteins and plant pathogenesis-related proteins. It is frequently expressed in human neuroblastoma and glioblastoma cell lines, and thus may play a role in the central nervous system.The deduced 258-amino acid protein has a predicted N-terminal signal sequence, a single N-glycosylation site, and an RRKR cleavage site. The mature secreted protein is predicted to contain 198-amino acids and to have a calculated molecular mass of about 23 kD. N-terminal sequencing of PI15 secreted from glioma cells confirmed cleavage of a prosequence. The purified protein shows an apparent molecular mass of 25 kD by SDS-PAGE. PCR analysis revealed expression in human brain, placenta, and lymphocyte cDNA.