The Mut+strain ofKomagataella phaffii(Pichia pastoris) expresses PAOX15 and 10 times faster than Mutsand Mut−strains: Evidence that formaldehyde or/and formate are true inducers of AOX

Abstract

AbstractThe methylotrophic yeastKomagataella phaffiiis among the most popular hosts for recombinant protein synthesis. Most recombinant proteins were expressed in the wild-type Mut+host strain from the methanol-inducible promoter PAOX1. Since methanol metabolism has undesirable consequences, two additional host strains, Muts(AOX1-) and Mut−(AOX1-AOX2-), were introduced which consume less methanol and reportedly also express recombinant protein better than Mut+. Both results follow from a simple model based on two widespread assumptions, namely methanol is transported by diffusion and the sole inducer of PAOX1. To test this model, we studied14C-methanol uptake in the Mut−strain and β-galactosidase expression in all three strains. We confirmed that methanol is transported by diffusion, but in contrast to the literature, Mut+expressed β-galactosidase 5- and 10-fold faster than Mutsand Mut−. These results imply that methanol is not the sole inducer of PAOX1— metabolites downstream of methanol also induce PAOX1. We find that formate or/and formaldehyde are probably true inducers since both induce PAOX1expression in Mut−which cannot synthesize intracellular methanol from formate or formaldehyde. Formate offers a promising substitute for methanol since it does not appear to suffer from the deficiencies that afflict methanol.