科研之友
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摘要
Fab' fragments have become an established class of biotherapeutic over the last two decades. Likewise, developments in synthetic biology are providing ever more powerful techniques for designing bacterial genes, gene networks and entire genomes that can be used to improve industrial performance of cells used for production of biotherapeutics. We have previously observed significant leakage of an exogenous therapeutic Fab' fragment into the growth medium during high cell density cultivation of an Escherichia coli production strain. In this study we sought to apply a promoter engineering strategy to address the issue of Fab' fragment leakage and its consequent bioprocess challenges. We used site directed mutagenesis to convert the P-tac promoter, present in the plasmid, pTTOD-A33 Fab', to a P-tic promoter which has been shown by others to direct expression at a 35% reduced rate compared to P-tac. We characterized the resultant production trains in which either P-tic or P-tac promoters direct Fab' fragment expression. The P-tic promoter strain showed a 25-30% reduction in Fab' expression relative to the original P-tac strain. Reduced Fab' leakage and increased viability over the course of a fed-batch fermentation were also observed for the P-tic promoter strain. We conclude that cell design steps such as the P-tac to P-tic promoter conversion reported here, can yield significant process benefit and understanding with respect to periplasmic Fab' fragment production. It remains an open question as to whether the influence of transgene expression on periplasmic retention is mediated by global metabolic burden effects or periplasm overcapacity.
- 出版日期2016-8
