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SA (streptavidin hereinafter referred to as SA) method is Streptomyces avidinii bacteria culture process secretion of a foreign protein product, can be highly water-soluble vitamin binding specificity, D-Biotin (D-biotin). SA-biotin system has a high affinity and specificity, high sensitivity, good stability, signal amplification, etc., SA-biotin system is widely used in medicine, immunology, molecular biology and tissue chemistry and other related fields. Currently SA mainly from the genus Streptomyces traditional fermented and genetically engineered bacteria exogenous expression, which has a short production cycle, high yield, easy purification, etc., produced in recent years become a hot research. E. coli expression system and the B. subtilis expression system is currently the most widely used two kinds of prokaryotic expression system. The former has the overexpression of exogenous proteins, producing widespread use of genetic and molecular biology clear background, etc., while the latter has an exocrine expression of foreign proteins, safe and reliable. In this paper the use of Bacillus subtilis and Escherichia coli expression system was expressed in various forms SA and refolding the expressed protein, the purpose is to explore the expression of high yield strain SA and SA efficient refolding solution. In this study, successful amplification by PCR gene encoding produces three SA: stv-13 (encoding amino acid residues 16-133), csa (encoding amino acid residues 13-139), cnsa (encoding amino acid residues 13-159 yl). The stv-13 was cloned into the expression vector pP43 B. subtilis and pSacR to construct B. subtilisWB800 (pSacR-stv-13) sucrose-inducible expression of bacteria, B. subtilis WB800 (pP43-stv-13) and B. subtilis168 (pP43 -stv-13) constitutive expression strains, but no significant exocrine protein expression. The stv-13, csa, cnsa cloned into E. coli expression vector pET22b, pET11a to construct into expression strain BL21 (DE3) (pET22b-stv-13), BL21 (DE3) (pET22b-csa), BL21 (DE3) (pET11a-cnsa), BL21 (DE3) pLysS (pET22b-stv-13), BL21 (DE3) pLysS (pET22b-csa), BL21 (DE3) pLysS (pET11a-cnsa), ER2566 (pET22b-stv-13), ER2566 (pET22b-csa), ER2566 (pET22b-cnsa), induced by IPTG, the results show BL21 (DE3) pLysS (pET11a-cnsa) SA highest expression. By expressing conditions and optimization of complex conditions, SA total bacterial protein expression more than 40%, and its inclusion body refolding efficiency above 80%. Refolded SA identified by ELISA showed that the commercialization of its biological activity slightly lower than the standard SA.
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