Cloning and characterization of a metalloprotease from Vibrio harveyi strain AP6

A metalloprotease gene pap6 was cloned from Vibrio harveyi strain AP6. Sequence analysis showed that pap6 was 2034 bp in length and predicted to encode a peptide of 677 amino acids with a molecular mass of 75 kDa. SDS-PAGE analysis of the purified Pap6 revealed that it was 35 kDa in size. N-terminal amino acid sequencing established that the mature protein began at Leu-191, suggesting that the preprotein of Pap6 was processed to generate a mature protease. Purified Pap6 was characterized as a zinc metalloprotease as it was inhibited by zinc- and metal-specific inhibitors such as 1, 10-phenanthroline, EGTA and EDTA. The deduced amino acid sequence revealed the presence of a zinc-binding motif HEXXH approximately 19aa approximately E. Substitution of these active site residues by site-directed mutagenesis caused significant losses in enzyme activity, thus demonstrating their involvement in catalysis. Pap6 was shown to digest a range of host proteins, including gelatin, fibronectin, and type IV collagen, indicating a potential role in pathogenesis.