CLONING, EXPRESSION, AND CHARACTERIZATION OF STRATUM-CORNEUM CHYMOTRYPTIC ENZYME - A SKIN-SPECIFIC HUMAN SERINE PROTEINASE

The cDNA encoding human stratum corneum chymo- tryptic enzyme (SCCE); an epidermal serine-proteinase which was recently purified from human stratum corneum, was isolated from a keratinocyte derived library. The obtained nucleotide sequence contained an open reading frame sufficie nt to encode a preproprotein consisting of 253 amino acid residues. Ex pression of two mRNA species hybridizing with SCCE cDNA, 1.2 and 2.0 k ilobases, respectively, was detected in human skin. These two forms di ffer with respect to the length of the 3'-untranslated sequence. Analy sis of mRNA derived from various human tissues showed that abundant ex pression of the SCCE gene was restricted to human skin. The cloned cDN A was introduced to a bovine papilloma virus-based expression system a nd recombinant protein was purified and characterized. The results sho w that recombinant SCCE is produced with a 22-amino acid residue signa l peptide and a propeptide of 7 amino acid residues. Tryptic digestion removed this propeptide and yielded a proteolytically active protein with the same NH2-terminal amino acid sequence as native SCCE. The ded uced amino acid sequence contains the conserved active site regions of serine proteinases. The calculated molecular mass of unglycosylated a ctive SCCE was 24.4 kDa. The sequence indicates one tentative N-glycos ylation site located near the C terminus. Recombinant SCCE was found t o be heterogenous regarding glycosylation in a manner similar to that of the native enzyme.