-!- This enzyme, derived from the house dust mite, is a major component of the allergic immune response. -!- The substrate specificity of this enzyme is not altogether clear; it cleaves the low-affinity IgE receptor CD23 at 298-Glu-|-Ser-299 and 155-Ser-|-Ser-156. -!- It also cleaves the pulmonary structural proteins occludin and claudin at Leu-|-Leu, Asp-|-Leu and at Gly-|-Thr bonds, and it can also cleave the alpha subunit of the interleukin-2 (IL-2) receptor (CD25). -!- Using a positional scanning combinatorial library, it was found that the major substrate-specificity determinant is for Ala in the P2 position. -!- The enzyme shows only a slight preference for basic amino acids in the P1 and P3 positions and a preference for aliphatic amino acids such as Ile, Pro, Val, Leu and norleucine in the P4 position. -!- Belongs to peptidase family C1.