Improving protein production from yeast
The yeast Pichia pastoris is commonly used to produce useful proteins ranging from food enzymes to pharmaceuticals. The genes encoding these ‘foreign’ proteins are cloned in place of a P. pastoris gene, AOX1, which ordinarily allows the yeast to grow in methanol. AOX1, and any foreign gene that replaces it, is regulated by enhancer and repressor proteins interacting with a DNA sequence called a promoter. When P. pastoris is grown in methanol, enhancer proteins switch on the AOX1 promoter; when grown in glucose, however, repressor proteins turn it off. The EU-funded AOX1 PROMOTER project investigated the mechanisms controlling AOX1 promoter activity. The aim was to create promoters and yeast strains with enhanced protein-production capabilities. To find potential enhancers and repressors, researchers searched for proteins that bind to the AOX1 promoter. They identified an enzyme complex involved in metabolism and two proteins, Mig1 and Mig2, that repress the AOX1 promoter when grown in glucose. They also found a protein called methanol expression regulatory protein 2 (Mxr2p), which was produced only in cells using methanol as a sole energy source. When Mxr2p was removed, P. pastoris lost its ability to grow in methanol, suggesting that Mxr2p activates the methanol-use pathway. Researchers used this information to create a yeast strain that over-produces the enhancer Mxr2p, and lacks the repressors Mig1 and Mig2, thereby increasing protein production. This strain will be useful to industry that requires large-scale protein production, and to academic scientists who produce proteins for experimental purposes.
Keywords
Protein production, yeast, Pichia pastoris, AOX1, methanol