PepJ is a new extracellular proteinase of Aspergillus nidulans

Under carbon starvation, Aspergillus nidulans released a metallo-proteinase with activities comparable to those of PrtA, the major extracellular serine proteinase of the fungus. The relative molar mass of the enzyme was 19 kDa as determined with both denaturing and renaturing SDS PAGE, while its isoelectric point and pH and temperature optima were 8.6, 5.5 and 65 °C, respectively. The enzyme was stable at pH 3.5–10.5 and was still active at 95 °C in the presence of azocasein substrate. MALDI-TOF MS analysis demonstrated that the proteinase was encoded by the pepJ gene (locus ID AN7962.3), and showed high similarity to deuterolysin from Aspergillus oryzae. The size of the mature enzyme, its EDTA sensitivity and heat stability also supported the view that A. nidulans PepJ is a deuterolysin-type metallo-proteinase.