Molecular cloning and targeted deletion of PEP2 which encodes a novel aspartic proteinase from Aspergillus fumigatus

Abstract

An aspartic proteinase PEP2 [EC 3.4.23.25] was purified from a cell wall fraction of Aspergillus fumigatus. The enzyme, which showed a broad range of activity from pH 2.0 to 7.0 and migrated as a single band of 39 kDa in SDS-PAGE, was not detected in the culture supernatant. A specific gene probe was designed on the basis of the N-terminal sequence of the native protein, and the PEP2 genomic and cDNA were isolated from corresponding libraries. The deduced amino acid sequence of PEP2 consists of 398 amino acids. A signal sequence of 18 amino acids and a proregion of another 52 amino acids were identified. The mature protein consists of 328 amino acids which include the two DTG-motifs of the active site common to almost all pepsin-like enzymes. PEP2 showed a 64% identity with the vacuolar proteinase A (PrA), of Saccharomyces cerevisiae, and an 88% identity with PEPE, an aspartic proteinase of Aspergillus niger. Recombinant PEP2 was over-expressed in Pichia pastoris and the active enzyme was secreted into the culture supernatant. Targeted deletion of PEP2 did not affect vegetative growth or cell and colony morphology. Identification of proteinases, such as PEP2, which are apparently associated with the Aspergillus cell wall raises new interest in these molecules with respect to their possible function in the pathogenesis of invasive aspergillosis.