Selenium Incorporation Into Recombinant HSA In Pichia Pastoris And Comparison Of Se Content In Various Leguminous Plants

Selenium (Se) is an essential trace element in the human body which is an important part of antioxidant enzymes that protect cells against adverse effects of free radicals produced during normal oxygen metabolism. Human serum albumin (HSA) plays an important role in clinical therapy. In our work, the recombinant protein contained Se is expected based on some yeasts are capable of accumulating large amounts of trace elements, such as Se, and incorporating them into organic compounds.The transgenic yeast Pichia pastoris cultured for high level expression of rHSA was fed with Na₂SeO₃ during the induction phase to investigate incorporation of selenium into rHSA. After fermentation, the supernatant was processed by heat treatment, ultrafiltration, ion exchanged chromatography and acetone precipitation and the molecule weight determined by Tricine-SDS-PAGE. Energy dispersive X-ray analysis (EDX) and atomic absorption spectroscopy (AAS) were then used to determine the selenium concentration. The results indicated that Na₂SeO₃ directly affects cell growth and rHSA yield. Furthermore, the experimental sample is found to contain 23.2% more selenium than the control (no addition of Na₂SeO₃) and the ratio of selenium to rHSA is 0.0069, which is about 35 times higher than the control. Our work primarily proved that inorganic Se can be converted into organic Se by Pichia pastoris and Se containing amino acids could be incorporated into rHSA.Some leguminous plants have the ability not only to grow in the presence of potential environmental contaminants, such as Se, but also to accumulate them. From the comparison of selenium content in various leguminous plants we found that the capability of accumulating Se of the bean No.9 and No. 10 which grew in low Se region is better than others, especially the bean No. 10 and the soybean No.1 which from high Se region also has the good ability to enrich Se. The optimum method of distilling Se-containing proteins is dunking, trituration, filtration, centrifugalism, acetone precipitation and drying.