BIOCHEMICAL AND ANTIGENIC CHARACTERIZATION OF A NEW DIPEPTIDYL-PEPTIDASE ISOLATED FROM ASPERGILLUS-FUMIGATUS

A novel dipeptidyl-peptidase (DPP V) was purified from the culture med ium of Aspergillus fumgatus. This is the first report of a secreted di peptidyl-peptidase. The enzyme had a molecular mass of 88 kDa and cont ained approximately 9 kDa of N-linked carbohydrate, The expression and secretion of dipeptidyl-peptidase varied with the growth conditions; maximal intra- and extracellular levels were detected when the culture medium contained only proteins or protein hydrolysates in the absence of sugars. The gene of DPP V was cloned and showed significant sequen ce homology to other eukaryotic dipeptidyl-peptidase genes. Unlike the other dipeptidyl-peptidases, which are all intracellular, DPP V conta ined a signal peptide. Like the genes of other dipeptidyl-peptidases, that of DPP V displayed the consensus sequences of the catalytic site of the nonclassical serine proteases, The biochemical properties of na tive and recombinant DPP V obtained in Pichia pastoris were unique and were characterized by a substrate specificity limited to the hydrolys is of X-Ala, Ris-Ser, and Ser-Tyr dipeptides at a neutral pH optimum. In addition, we showed that DPP V is identical to one of the two major antigens used for the diagnosis of aspergillosis.