Methanol expression regulator 1 (Mxr1p) promotes xylulose 5-phosphate recycle via increaseing transketolase activity in Pichia pastoris

Abstract Background Methanol expression regulator 1 (Mxr1p) is a key transcription factor that plays a vital role in the methanol utilization pathway in Pichia pastoris ( P. pastoris ). Most genes referred to the methanol utilization pathway were regulated by Mxr1p. However, some genes did not show a significant difference between methanol and glycerol even though they play an important role in the methanol utilization pathway. So far, the regulation mechanism about these genes and the relationship with Mxr1p are still unknown. Results Methanol metabolic pathway analysis revealed that most of the methanol-induced genes were upregulated in transcriptional level when cultured in methanol. Whereas some genes like tkl1 (transketolase 1) did not show significant up-regulation in methanol even though it plays a very important role in Xu5P recycle, the reason is still not clear. To clarify this point, firstly, pull-down and MS experiments were performed. The result shows that Tkl1p protein combined with Mxr1p in vitro . Subsequently, this result was further confirmed by yeast two-hybrid in vivo , and the binding region mainly located from 150AA to 400AA. Moreover, Ser215 phosphorylation did not affect this interaction. In addition, Mxr1p-400AA integration into Δmxr1 could rescue cell growth in methanol. All the above results proved that Mxr1p played a post-translational role in the methanol utilization pathway and Mxr1p-400AA may achieved most of Mxr1p functions. Secondly, the function of Mxr1p-Tkl1p complex was expounded by detecting formaldehyde consumption and xylulose production in cell-free systems. Results showed that Mxr1p-Tkl1p mixture could promote formaldehyde consumption and xylulose production in vitro . Conclusion Mxr1p promotes methanol utilization via combining with Tkl1p to accelerate Xu5P recycle and this interaction was not affected by Ser215 phosphorylation.