Human Tryptase ε (PRSS22), a New Member of the Chromosome 16p13.3 Family of Human Serine Proteases Expressed in Airway Epithelial Cells

Probing of the GenBank™ expressed sequence tag (EST) data base with varied human tryptase cDNAs identified two truncated ESTs that subsequently were found to encode overlapping portions of a novel human serine protease (designated tryptase ε or protease, serine S1 family member 22 (PRSS22)). The tryptase ε gene resides on chromosome 16p13.3 within a 2.5-Mb complex of serine protease genes. Although at least 7 of the 14 genes in this complex encode enzymatically active proteases, only one tryptase E-like gene was identified. The trachea and esophagus were found to contain the highest steady-state levels of the tryptase ε transcript in adult humans. Although the tryptase ε transcript was scarce in adult human lung, it was present in abundance in fetal lung. Thus, the tryptase ε gene is expressed in the airways in a developmentally regulated manner that is different from that of other human tryptase genes. At the cellular level, tryptase ε is a major product of normal pulmonary epithelial cells, as well as varied transformed epithelial cell lines. Enzymatically active tryptase ε is also constitutively secreted from these cells. The amino acid sequence of human tryptase ε is 38-44% identical to those of human tryptase α, tryptase βI, tryptase βII, tryptase βIII, transmembrane tryptase/tryptase γ, marapsin, and Esp-1/testisin. Nevertheless, comparative protein structure modeling and functional studies using recombinant material revealed that tryptase ε has a substrate preference distinct from that of its other family members. These data indicate that the products of the chromosome 16p13.3 complex of tryptase genes evolved to carry out varied functions in humans.