Expression, Purfication and endotoxin removal of Brucella melitensis DnaK and Omp31 proteins

New strategies are needed to protect against Brucella melitensis infection. Subunit vaccines offer a promising approach because they can stimulate both cellular and humoral immunity, so high production of recombinant protein with less content of endotoxin is desired. In present study, we described a method for expression and purification of B.melitensis recombinant DnaK(rDnaK) and Omp31(rOmp31) proteins while less content of endotoxins were detected in final product. Recombinant pET-dnak and pDEST-omp31 plasmids were transformed into competent expression host E.coli BL21 (DE3). After induction by IPTG, bacteria were grown at 20◦C for 22h. Then recombinant proteins were purified by Ni-NTA Agarose. Purification was done while two methods using Triton X-114 in washing steps and standard protocol (without detergent) were used in parallel. rDnak and rOmp31 were purified by using Urea. We could obtain 20 and 8 mg recombinant proteins from rDnak and rOmp31 from 1 liter medium, respectively. The amount of endotoxins in final products was less content of 0.05 EU/mg. Furthermore, recovery of protein was up to 80% as compared to the standard protocol. The method used in this study, gives a product with very low extent of endotoxin, but 20% of recombinant proteins were lost. So we think the method described here can be used for purification and endotoxin removal of other recombinant proteins with similar physiologic properties.