Purification and Characterisation of a Burkholderia pseudomallei Protease Expressed in Recombinant E. coli

A genomic DNA fragment that contains the gene, which codes for a novel extracellular serine protease in Burkholderia pseudomallei, was cloned by using pQE40 as a vector. It was maintained in Escherichia coli JM109. The expression of the gene(s) resulted in the production of a 52 kDa protease. The recombinant protease was purified from the culture filtrate via ammonium sulfate fractionation, gel filtration, and anion-exchange chromatography. The purified protease had an optimum pH and temperature of pH 8.9 and $38^{\circ}C$, respectively. The protease activity was inhibited by EGTA, EDTA, and PMSF, but not 1,10-phenanthroline. The first 11 amino acid residues from the N-terminus of the purified protease were identified as LAPNDPYYYGY. PNDPYY was found to show homology to the Bacillus cereus microbial serine protease and B. subtilis PD498 serine protease. These results indicate that the protease that was purified in this study is an extracellular calcium-dependent serine protease. The purified protease was able to digest the human serum 19A, IgG, albumin, and transferrin, as well as bovine muscle actin and myosin. Furthermore, it was able to promote or cause dermonecrosis in experimental rabbits. These results propose the possible role of a novel B. pseudomallei extracellular calcium-dependent serine protease in the virulence of the pathogen.