| Periplasmic expression of rhGH in Escherichia coli was propitious to avoid antigenicity in its clinic application and convenient for purification. Therefore, in modern industry secretary expression of rhGH was being in favor. The engineering bacteria expressing rhGH in secretion type was constructed by using T7 promoter and ompA3 leader sequence. The effect of phosphate, yeast extract and lactose on expression level of rhGH was determined by orthogonal test, and the influence of different starting glucose concentration on rhGH expression level was also studied to optimize culture medium compositions. Induction stage, induction temperature, IPTG concentration and expression time were studied to optimize condition in secretory expression of rhGH in engineering bacteria. rhGH expression conditions and level of engineering bacteria in fermentation were based on results obtained in shaking flasks. Engineered pET-ompA3-hGH/BL21(DE3) expressed secretion rhGH by inducing and supplying nutrimental components in 5 L fermentor. Expression level of rhGH could reach 250 mg/L culture solution by means of selecting components of original culture media, components of supplemental media, volume of supplemental media, the time of supplying supplemental media and supplying speed of supplemental media, secretion rhGH was found to represent 44%-54% of the total proteins in periplasm, and the fermentation time was reduced to 8 hrs. Secretion rhGH was purified in one-step with affinity chromatography prepared by the polyclonal antibodies from the rabbit immunized with rhGH, and homogeneous rhGH was obtained, with the purity above 96% identified with reduced and nonreduced SDS-PAGE and reversed-phase HPLC. The molecular mass size, immunity activity and formation of disulphide bond were identical to those of native hGH.
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