Molecular and biochemical characterization of a serine proteinase predominantly expressed in the medulla oblongata and cerebellar white matter of mouse brain

A full-length cDNA clone of a serine proteinase, mouse brain serine protein ase (mBSP), was isolated from a mouse brain cDNA library. mBSP, which has b een recently reported to be expressed in the hair follicles of nude mice, i s most similar (88% identical) in sequence to rat myelencephalon-specific p rotease, The mBSP mRNA was steadily expressed in the brain of adult mice wi th a transient expression in the early fetal stage during development. The genomic structure of the mouse gene for mBSP was determined. The gene, whic h is mapped to chromosome 7B4-B5, is about 7.4 kilobases in size and contai ns 7 exons, Interestingly, the 5'-untranslated region of the mBSP gene was interrupted by two introns, In situ hybridization analyses revealed that mB SP is expressed in the white matter of the cerebellum, medulla oblongata, a nd capsula interna and capsula interna pars retrolenticularis of mouse brai n. Further, mBSP was immunolocalized to the neuroglial cells in the white m atter of the cerebellum. Recombinant mBSP was produced in the bacterial exp ression system and activated by lysyl endopeptidase digestion, and the acti vated enzyme was purified for characterization. The enzyme showed amidolyti c activities preferentially cleaving Arg-X bonds when 4-methylcoumaryl-7-am ide-containing peptide substrates were used. Typical serine proteinase inhi bitors, such as diisopropyl fluorophosphates, phenylmethanesulfonyl fluorid e, soybean trypsin inhibitor, aprotinin, leupeptin, antipain, and benzamidi ne, strongly inhibited the enzyme activity, The recombinant mBSP effectivel y hydrolyzed fibronectin and gelatin, but not laminin, collagens I and IV, or elastin. These results suggest that mBSP plays an important role in asso ciation with the function of the adult mouse brain.