Functional analysis of the Burkholderia cenocepacia ZmpA metalloprotease

Burkholderia cenocepacia ZmpA is expressed as a preproenzyme typical of thermolysin-like proteases such as Pseudomonas aeruginosa LasB and Bacillus thermoproteolyticus thermolysin. The zmpA gene was expressed using the pPRO-EXHTa His(6) tag expression system, which incorporates a six-His tag at the N-terminal end of the protein, and recombinant ZmpA was purified using Ni-nitrilotriacetic acid affinity chromatography. Upon refolding of the recombinant His(6)-pre-pro-ZmpA (62 kDa), the fusion protein was autoproteolytically cleaved into 36-kDa (mature ZmpA) and 27-kDa peptides. Site-directed mutagenesis was employed to infer the identity of the active site residues of ZmpA and to confirm that the enzyme undergoes autoproteolytic cleavage. Oligonucleotide mutagenesis was used to replace H-465 with G(46), or A(465), E-377 with A(377) or D-377, or H-380 with P-380 or A(380). Mutagenesis of H-465, E-377, or H-380 resulted in the loss of both autocatalytic activity and proteolytic activity. ZmpA with either substitution in H-380 was not detectable in B. cenocepacia cell extracts. The activity of the recombinant ZmpA was inhibited by EDTA and 1,10 phenanthroline, indicating that it is a zinc metalloprotease. ZmpA, however, was not inhibited by phosphoramidon, a classical inhibitor of the thermolysin-like proteases. The refolded mature ZmpA enzyme was proteolytically active against various substrates including hide powder azure, type IV collagen, fibronectin, neutrophil alpha-1 proteinase inhibitor, alpha(2)-macroglobulin, and gamma interferon, suggesting that B. cenocepacia ZmpA may cause direct tissue damage to the host or damage to host tissues through a modulation of the host's immune system.