Purification and characterization of an extracellular serine protease from the nematode-trapping fungus Dactylella shizishanna

Aims: To evaluate the production of an extracellular serine protease by Dactylella shizishanna and its potential as a pathogenesis factor. Methods and Results: An extracellular alkaline serine protease (Ds1) was purified and characterized from the nematode-trapping fungus D. shizishanna using cation-exchange chromatography and hydrophobic interaction chromatography. The molecular mass of the protease was approximately 35 kDa estimated by SDS-PAGE. The optimum activity of Ds1 was at pH 10 and 55 degrees C (over 30 min). The purified protease could degrade purified cuticle of Penagrellus redivivus and a broad range of protein substrates. The purified protease was highly sensitive to phenylmethyl sulfonyl fluoride (PMSF) (0.1 mmol l(-1)), indicating it belonged to the serine protease family. The N-terminal amino acid residues of Ds1 are AEQTDSTWGL and showed a high homology with Aozl and PII, two serine proteases purified from the nematode-trapping fungus Arthrobotrys oligospora. Conclusions: Nematicidal activity of D. shizishanna was partly related to its ability to produce extracellular serine protease. Significance and Impact of the Study: In this report, we purified a new serine protease from D. shizishanna and provided a good foundation for future research on infection mechanism.