Expression and enzyme activity analysis of Djtry in planarian Dugesia japonica

: The cDNA Djtry, encoding a planarian trypsin, was identified from the cDNA library of Dugesia japonica. Multiple alignment analysis showed that the Tryps_SPc domain contained the incompletely conserved catalytic triad in which the first amino acid His was substituted by Lys. Phylogenetic analysis indicateed that Djtry protein falls at the base of other animal trypsins. The Djtry cDNA was cloned into a bacterial vector pET-28a and was transferred into E. coli BL21. The His-tagged Djtry fusion protein expression was induced by IPTG. SDS-PAGE analysis revealed that the Djtry was expressed as inclusion bodies in E. coli BL21 with the estimated molecular weight of approximately 26 kDa. Western blotting with His-tag antibody showed that the antibody was reacted with the fusion protein after refolding. Compared to bovine trypsin using BAEE as special substrate of trypsin, the enzyme activity of Djtry was measured. These results indicate that Djtry represents the archetype of animal trypsins, and this type of mutational trypsin Djtry still performs the trypsin nature with slightly weaker activity.