Molecular cloning of a novel brain-specific serine protease with a kringle-like structure and three scavenger receptor cysteine-rich motifs.

In order to find serine proteases specifically expressed in brain, we designed degenerate mixed primers for consensus sequences of serine protease domains. By PCR utilizing the primers, we have cloned a novel sequence from reverse transcripts of total RNA of mouse brain and used it as a probe to screen a mouse brain cDNA library. Overlapping cDNAs encoding a precursor of a novel brain specific serine protease (BSSP-3) were cloned. DNA insert of the longest clone consisted of 2614-bp with an entire open reading frame encoding a secretory/membrane-anchored precursor protein consisting of 761 amino acids (AA) which may be processed to yield an active enzyme of 245 AA. As found in known serine proteases, BSSP-3 enzyme domain contained a catalytic triad which consists of AA residues essential for the enzyme activity. In the upstream region of the enzyme domain that resides at C-terminus of the precursor protein, there are, from N-terminus to downstream, a sequence similar to a kringle structure and three repetitive ones highly similar to the scavenger receptor cysteine-rich (SRCR) motifs. Northern blot analysis demonstrated that mBSSP-3 mRNA was specifically expressed in the mouse brain, lung and kidney. We concluded that a novel brain serine protease, BSSP-3, is a new member of kringle and SRCR superfamilies. Copyright 1997 Academic Press.