Molecular cloning and characterization of mouse mast cell chymases

Mouse mast cell chymases are granule-associated serine proteinases with chymotrypsin-like substrate specificities. cDNAs for two new chymases were isolated from a cDNA library constructed using mRNA from ABFTL-6 mouse mast cells by screening with a rat mast cell proteinase cDNA. The deduced amino acid sequence of mouse chymase 1 consists of a 226 amino acid catalytic portion and a 21 amino acid preprosequence. Chymase 1 is unusual in that an Asn occurs in the substrate binding pocket, a feature that has not been observed in any other serine proteinase. Also, chymase 1 is expected to have a large positive charge (+13) at physiological pH. A partial cDNA for chymase 2 encodes 177 residues of the carboxy terminal portion of a second proteinase distinct from chymase 1. Chymase 2 cDNA contains a highly conserved intron/exon junction, a high positive charge (+17) and a novel, second potential N-glycosylation site. Transcripts for both chymases are found in ABFTL-6 mast cells, but only chymase 2 mRNA is in mouse connective tissue mast cells. These data suggest that these chymases have distinct enzymatic properties and tissue-specific patterns of gene expression.