Pitcher plants are insectivorous and secrete a digestive fluid into the pitcher. This fluid contains a mixture of enzymes including peptidases. One of these is neprosin, characterized from the pitcher plant Nepenthes ventrata. This peptidase is of unknown catalytic type and is unaffected by standard peptidase inhibitors. Unusually, activity is directed towards prolyl bonds, but unlike most peptidase that cleave after proline, there is no restriction on sequence length or position of the proline residue. The peptidase is secreted and is presumed to possess an N-terminal activation peptide. The neprosin domain corresponds to the mature peptidase [1]. It is not known if other proteins with this domain are peptidases.

1: Addressing proteolytic efficiency in enzymatic degradation therapy for celiac disease. Rey M, Yang M, Lee L, Zhang Y, Sheff JG, Sensen CW, Mrazek H, Halada P, Man P, McCarville JL, Verdu EF, Schriemer DC; Sci Rep. 2016;6:30980. PMID:27481162