Molecular characterization and comparative study of 6 salivary gland metalloproteases from the hard tick, Haemaphysalis longicornis

Six genes encoding metalloproteases were identified from the salivary gland of the hard tick, Haemaphysalis longicornis. Comparative analyses have shown the evolutionary distinct and different mRNA expression patterns of each gene during blood feeding. The proteins are synthesized as proenzymes with a prodomain and a metalloprotease/cysteine-rich domain of the reprolysin family. Within the active site, amino acid substitutions were observed. The recombinant Escherichia coli expression of one gene, hlESTMP1, was performed. The immunoblot analysis and indirect fluorescent assay using anti-hlESTMP1 suggested that this protein is mainly expressed in the cytoplasm of the salivary glands and only the mature form of 34 kDa was detectable. The proenzyme expressed by baculovirus was processed into a mature domain, suggesting that proenzyme activation possibly occurs through a pro-protein convertase dependent pathway. The presence of these diverse enzymes might contribute to the greater functional complexity of bioactive molecules in tick saliva to facilitate blood feeding.