Extracellular peptidase in the fungal pathogen Pseudallescheria boydii

Pseudallescheria boydii is a ubiquitous filamentous fungus capable of causing invasive disease in humans. In the present study, using sodium dodecyl sulfate-polyacrylamide gels containing bovine serum albumin as co-polymerized substrate, we identified a 28-kDa proteolytic activity released to the extracellular environment by mycelia of P. boydii. This peptidase was detected during the growth of P. boydii in Sabouraud-dextrose medium for 13 days and reached its maximal production on day 7. The 28-kDa peptidase was active in acidic pH (5.5) and had its activity completely blocked by 1,10-phenanthroline, a potent zinc-metallopeptidase inhibitor. Two other metallopeptidase inhibitors, EDTA and EGTA, were also tested and no alterations were observed in the activity of the 28-kDa extracellular peptidase. Likewise, E-64 (a cysteine peptidase inhibitor), phenylmethylsulphonyl fluoride (a serine peptidase inhibitor), and pepstatin A (an aspartyl peptidase inhibitor) did not significantly alter the enzymatic behavior. Collectively, we described for the first time the expression of an extracellular metallopeptidase in the human opportunistic fungal pathogen P. boydii.