Cost-effective manufacturing of biopharmaceuticals in non-mammalian hosts still requires tremendous efforts in strain development. In order to expedite identification of novel leads for strain engineering, we used a transposon-mutagenized yeast genomic DNA library to create a collection of Saccharomyces cerevisiae deletion strains expressing a full-length IgG antibody. Using a high-throughput screening, transformants with either significantly higher or lower IgG expression were selected. The integration site of the transposon in three of the selected strains was located by DNA sequencing. The inserted DNA lay within the VPS30 and TAR1 open reading frame, and upstream of the HEM13 open reading frame. The complete coding sequence of these genes was deleted in the wild-type strain background to confirm the IgG expression phenotypes. Production of recombinant antibody was increased 2-fold in the Delta vps30 strain, but only mildly affected secretion levels in the Delta tar1 strain. Remarkably, expression of endogenous yeast acid phosphatase was increased 1.7- and 2.4-fold in Delta vps30 and Delta tar1 strains. The study confirmed the power of genome-wide high-throughput screens for strain development and highlights the importance of using the target molecule during the screening process.
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