Abstract: The superfamily of cysteine protease inhibitor consists of proteins which can inhibit the hydrolytic activity of cysteine proteinases. In this study, MdCPI, a gene of cysteine protease inhibitor was cloned from housefly (Musca domestica)by RACE based on dbEST information. It contains a 357 bp open reading frame encoding 118 amino acid residues. The deduced peptide contains a putative signal peptide of 17 amino acids. The amino acid sequence of MdCPI showed the highest homology with that of Sarcophaga crassipalpis  (identity=51%) in the homologous assay. The phylogenetic tree indicates that the CPIs from housefly and other dipterans have descended from a single common ancestor and belong to I25A family. To understand the inhibitory activity of MdCPI to cysteine protease, a prokaryotic expression vector pET-17b-MdCPI was constructed and then expressed in Escherichia coli BL21. The results of activity detection showed that about 1 μg recombinant MdCPI could inhibit the activity of 14 μg papain. The results suggest that MdCPI is the member of the CPI supperfamily, and may have similar functions and be involved in immunological and physiological regulation. The successful cloning, expression and activity detection of MdCPI provided a basis for the further study on its function.

Key words: Musca domestica, cysteine protease inhibitor, cloning, recombinant expression, inhibitory activity