Expressão heteróloga da enteroquinase em enzima Escherichia coli

Abstract

Enterokinase (EC 3.4.21.9) is a heterodimer serine protease, a natural activator of trypsinogen, capable of cleaving specifically the sequence Asp-Asp-Asp-Asp-Lys. Due to the high specificity of the recognition site, it became a great tool of biotechnological interest. It is usually used to remove affinity tags in vitro, of recombinant proteins. In this work, the molecular cloning strategy resulted in the construction of the pDMK06, capable of programming the regulated expression of a heterologous gene ETK-Trx in E. coli. Through the cleavage process with restriction enzymes NdeI and BamHI, it was possible to obtain the coding sequence of the fusion protein between enterokinase and thioredoxin (ETK-Trx) of approximately 1259 bp from pENTK plasmid. Then, this sequence was subcloned at NdeI and BamHI sites of the expression vector pDM02, originating the recombinant plasmid pDMK06. This vector contains the TH2 promoter, which is efficiently regulated by Lac operator/repressor. E. coli JM110 cells transformed with the recombinant plasmid showed smaller growth in a solid medium when the expression of the heterologous protein was induced by IPTG in comparison with the control; however, this effect was not detected in the liquid medium. Furthermore, the E. coli cells morphology was analyzed through optical microscopy containing the recombinant plasmid pDMK06, when it was observed, all through the growth time, modifications on cell morphology, characterized by the formation of filaments in those induced with IPTG, in comparison with the control. For expression analysis of the recombinant protein ETKTrx, polyacrylamide gel electrophoresis SDS-PAGE was performed with the samples that grew with IPTG induction for eight hours. The results showed that the protein ETK-Trx is about 47 kDa with a high level of expression at the insoluble fraction, probably as an inclusion corpuscle. The high levels of expression of ETK-Trx protein occurred in a perfectly regulated way, showing the functionality of the pDM02 plasmid expression/regulation system.