Project description:The Crabtree phenotype defines whether a yeast can perform simultaneous respiration and fermentation under aerobic conditions at high growth rates, a phenomenon that resembles the Warburg effect in cancer cells. Whole genome duplication, global promoter rewiring and loss of respiratory complex I are the main molecular events that contributed to the evolution of Crabtree effect. Here we show that overexpression of a single Gal4-like transcription factor is sufficient to convert Crabtree-negative Komagataella phaffii (Pichia pastoris) into a Crabtree positive yeast. We report the transcriptome profile (RNASeq) of the Δgal4-like and Gal4-like overexpression K. phaffii strains. Upregulation of the glycolytic genes and a significant increase in glucose uptake rate due to the overexpression of the Gal4-like transcription factor caused an overflow metabolism, triggering both short-term and long-term Crabtree phenotypes. This indicates that a single mutation leading to overexpression of one gene may have been sufficient as a first molecular event towards respiro-fermentative metabolism in the course of yeast evolution.
Project description:We analyzed the chromatin accessibility and nucleosome positioning by ATAC-seq of both null and transgene-expressing strains of Komagataella phaffii (Pichia pastoris) under different growth conditions. These data enabled identification of the features that determine performance of various integration sites for transgene expression. Understanding chromatin accessibility and nucleosome positioning can provide further clarity into gene regulation and expression broadly in this organism.
Project description:Prevention of COVID-19 on a global scale will require the continued development of high-volume, low-cost platforms for the manufacturing of vaccines to supply on-going demand. Vaccine candidates based on recombinant protein subunits remain important because they can be manufactured at low costs in existing large-scale production facilities that use microbial hosts like Komagataella phaffii (Pichia pastoris). Here, we report an improved and scalable manufacturing approach for the SARS-CoV-2 spike protein receptor binding domain (RBD); this protein is a key antigen for several reported vaccine candidates. We genetically engineered a manufacturing strain of K. phaffii to obviate the requirement for methanol-induction of the recombinant gene. Methanol-free production improved the secreted titer of the RBD protein by >5x by alleviating protein folding stress. Removal of methanol from the production process enabled scale up to a 1,200 L pre-existing production facility. This engineered strain is now used to produce an RBD-based vaccine antigen that is currently in clinical trials and could be used to produce other variants of RBD as needed for future vaccines.
