Purification and characterization of a novel extracellular neutral metalloprotease from Cerrena albocinnamomea

We selected a fungus secreting a neutral protease from soil and identified it as the basidiomycete fungus Cerrena albocinnamomea according to its ITS-5.8S rDNA and 28S rDNA-D1/D2 sequences. A major extracellular protease isolated from C. albocinnamomea was purified approximately 44-fold through two purification steps. SDS-PAGE analyses of the purified protease revealed a single band, and its molecular mass of 39,756 Da was determined using MALDI-TOF-MS. The enzyme was optimally active at approximately pH 7.0 and 45°C. The K_m and V_max values for the hydrolysis of azocasein were 2.46 mg/mL and 989 units/min/mg protein, respectively. The enzyme was stable at pH 3.6-8.6 for 16 h and at temperatures ≤35°C for 1 h. Enzymatic activity was completely inhibited by Cu²⁺ and Zn²⁺ and markedly by EDTA and phosphoramidon. The N-terminal amino acid sequence ASYRVLPIT is highly similar to those of the members of the metalloprotease family M36, such as keratinase and elastinase. However, the protease did not detectably hydrolyze keratin or elastin. In contrast, the protease hydrolyzed fibrinogen, although there were no significant sequence similarities to the N-terminal amino acid sequences of other fibrinolytic enzymes. These results suggest that the purified protease represents a new neutral metalloprotease with fibrinogenolytic activity.