Microbiology; co-auth PAF

Microbiology. 2011 Feb 24. [Epub ahead of print]

Secreted glutamic protease rescues aspartic protease Pep deficiency in Aspergillus fumigatus during growth in acidic protein medium.

Sriranganadane D, Reichard U, Salamin K, Fratti M, Jousson O, Waridel P, Quadroni M, Neuhaus JM, Monod M.

Department of Dermatology, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland;

Abstract

In an acidic protein medium Aspergillus fumigatus secretes an aspartic endoprotease (Pep) as well as tripeptidyl-peptidases, a prolyl-peptidase and carboxypeptidases. In addition, we have identified by LC-MS/MS a novel glutamic protease, AfuGprA, homologous to Aspergillus niger aspergillopepsin II. The importance of AfuGprA in protein digestion was evaluated by deletion of its encoding gene in A. fumigatus wild type D141 and in a pepA mutant. We have shown that either A. fumigatus Pep or AfuGprA is necessary for fungal growth in protein medium at acidic pH. Exoproteolytic activity is therefore not sufficient for complete protein hydrolysis and fungal growth in a medium containing proteins as the sole nitrogen source. Pep and AfuGprA constitute a pair of endoproteases active at acidic pH in analogy to A. fumigatus alkaline protease (Alp) and metalloprotease I (Mep), where at least one of these enzymes is necessary for fungal growth in protein medium at neutral pH. Heterologous expression of AfuGprA in Pichia pastoris showed that the enzyme is synthesized as a preproprotein and that the propeptide is removed through an autoproteolytic reaction at acidic pH to generate the mature protease. In contrast to A. niger aspergillopepsin II, AfuGprA is a single chain protein and is structurally more similar to G1 proteases characterized in other non-Aspergillus fungi.

PMID: 21349972 [PubMed - as supplied by publisher]