The Burkholderia pseudomallei serine protease MprA is autoproteolytically activated to produce a highly stable enzyme

Burkholderia pseudomallei, a tropical pathogen and the causative agent of melioidosis, is known to secrete a serine metalloprotease (MprA) into the internal milieu of the infectious host. This protein has been shown to cause extensive damage to mammalian physiological proteins and its role in the pathogenesis of melioidosis is still under investigation. Previously, we have reported on the epitope mapping of B. pseudomallei protease that revealed a consensus peptide sequence of serine–methionine–alanine (SMA). The serine within this motif is involved in the serine protease catalytic triad and the SMA domain of the B. pseudomallei serine protease could be a major immunodominant domain. We undertook to further characterize the mprA gene and protein to gain deeper insight into the role and mechanism of this protein. Preliminary analysis showed that the crude lysate of expressed recombinant protease was able to hydrolyze gelatin, azocasein and skimmed milk. Further biochemical characterization demonstrated that the expressed protein maintained good proteolytic activity over a wide pH range of 5–11, is stable from 4 °C up to 68 °C and partially digested immunoglobulins A and G, transferrin and myosin. The proteolytic activity was strongly inhibited by phenylmethylsulfonyl fluoride. From our in vitro experimental evidence, we propose a proenzyme processing mechanism similar to that of subtilisin to produce the mature active protease.