Purification and characterization of a novel prolyl endopeptidase from Aspergillus niger

Abstract

A novel prolyl endopeptidase has been purified to homogeneity and characterized from the crude extract powder of the culture filtrate of Aspergillus niger var. macrosporus. It was shown to be a monomeric protein with a molecular weight of approximately 54,500, cleaving Pro-X bonds not only in oligopeptides but also in proteins. It has a pH optimum at around 3.7 and is strongly inhibited by diisopropylfluorophosphate, thus being an acid serine endopeptidase. Comparison of the amino acid sequences of related peptidases in the database indicates that it belongs, not to the serine peptidase family S9 which includes prolyl oligopeptidase, but to the serine peptidase family S28 which includes Pro-specific exopeptidases, such as lysosomal Pro-X carboxypeptidase and dipeptidyl peptidase II.