A novel methanol-free Pichia pastoris system for recombinant protein expression

BACKGROUND: As one of the most popular expression systems, recombinant protein expression in Pichia pastoris relies on the AOX1 promoter (P(AOX1)) which is strongly induced by methanol. However, the toxic and inflammatory nature of methanol restricts its application, especially in edible and medical products. Therefore, constructing a novel methanol-free system becomes necessary. The kinases involved in P(AOX1) activation or repression by different carbon sources may be promising targets. RESULTS: We identified two kinase mutants: Δgut1 and Δdak, both of which showed strong alcohol oxidase activity under non-methanol carbon sources. Based on these two kinases, we constructed two methanol-free expression systems: Δgut1-HpGCY1-glycerol (P(AOX1) induced by glycerol) and Δdak-DHA (P(AOX1) induced by DHA). By comparing their GFP expression efficiencies, the latter one showed better potential. To further test the Δdak-DHA system, three more recombinant proteins were expressed as examples. We found that the expression ability of our novel methanol-free Δdak-DHA system was generally better than the constitutive GAP promoter, and reached 50–60 % of the traditional methanol induced system. CONCLUSIONS: We successfully constructed a novel methanol-free expression system Δdak-DHA. This modified expression platform preserved the favorable regulatable nature of P(AOX1), providing a potential alternative to the traditional system. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12934-016-0578-4) contains supplementary material, which is available to authorized users.