Proline iminopeptidase; part of the gene cluster that mediates the biosynthesis of dihydroxynaphthalene (DHN)-melanin, a bluish-green pigment forming a dark layer in the conidial wall that protects the conidia from UV radiations (PubMed:28517364). The first step of the pathway is the production of the pentaketide 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN or T4HN) by the polyketide synthase PfmaE though condensation of acetyl-CoA with malonyl-CoA. T4HN is not stable and easily oxidizes into the stable form flaviolin (PubMed:28517364). T4HN is also substrate of the hydroxynaphthalene reductase PfmaG to yield scytalone (PubMed:28517364). The scytalone dehydratase PfmaJ then reduces scytalone to 1,3,8-THN (PubMed:31116900). 1,3,8-THN is then substrate of the hydroxynaphthalene reductase PfmaI to yield vermelone (Probable). Vermelone is further converted by the multicopper oxidase PfmaD to 1,8-DHN (Probable). Finally the laccase PFICI_06862 transforms 1,8-DHN to DHN-melanin (Probable). The roles of the 5-oxoprolinase PfmaA and the proline iminopeptidase PfmaB within the cluster have not been elucidated yet (Probable). Release of N-terminal proline from a peptide. Does not affect the production of scytalone. Belongs to the peptidase S33 family.