Figure 1.

Airway trypsin-like proteases (TLPs). β-tryptase is released from mast cells in the airway epithelium in its active heterotrimeric form. Prostasin is a glycophosphatidylinositol (GPI)-anchored protein that contains a serine protease catalytic domain. The type II transmembrane serine proteases (TTSPs) are illustrated with their conserved serine protease domain linked to their respective extracellular domains (SEA, sea urchin sperm protein, enterokinase and agrin; LDLA, low-density lipoprotein receptor A; group A scavenger receptor; CUB C1s/C1r, urchin embryonic growth factor and bone morphogenetic protein-1) and transmembrane domains. Amino and carboxy termini are indicated by N and C, respectively.