Wayman Joseph A, Glasscock Cameron, Mansell Thomas J, DeLisa Matthew P, Varner Jeffrey D
School of Applied and Engineering Physics, Cornell University, Ithaca, NY, 14853, USA.
Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY, 14853, USA.
Metab Eng Commun. 2019 Mar 29;9:e00088. doi: 10.1016/j.mec.2019.e00088. eCollection 2019 Dec.
Asparagine-linked (-linked) glycosylation is the most common protein modification in eukaryotes, affecting over two-thirds of the proteome. Glycosylation is also critical to the pharmacokinetic activity and immunogenicity of many therapeutic proteins currently produced in complex eukaryotic hosts. The discovery of a protein glycosylation pathway in the pathogen and its subsequent transfer into laboratory strains of has spurred great interest in glycoprotein production in prokaryotes. However, prokaryotic glycoprotein production has several drawbacks, including insufficient availability of non-native glycan precursors. To address this limitation, we used a constraint-based model of metabolism in combination with heuristic optimization to design gene knockout strains that overproduced glycan precursors. First, we incorporated reactions associated with glycan assembly into a genome-scale model of metabolism. We then identified gene knockout strains that coupled optimal growth to glycan synthesis. Simulations suggested that these growth-coupled glycan overproducing strains had metabolic imbalances that rerouted flux toward glycan precursor synthesis. We then validated the model-identified knockout strains experimentally by measuring glycan expression using a flow cytometric-based assay involving fluorescent labeling of cell surface-displayed glycans. Overall, this study demonstrates the promising role that metabolic modeling can play in optimizing the performance of a next-generation microbial glycosylation platform.
天冬酰胺连接(N-连接)糖基化是真核生物中最常见的蛋白质修饰,影响超过三分之二的蛋白质组。糖基化对于目前在复杂真核宿主中生产的许多治疗性蛋白质的药代动力学活性和免疫原性也至关重要。在病原体中发现蛋白质糖基化途径并随后将其转移到实验室菌株中,激发了人们对原核生物中糖蛋白生产的极大兴趣。然而,原核生物糖蛋白生产存在几个缺点,包括非天然聚糖前体的可用性不足。为了解决这一限制,我们使用基于约束的代谢模型结合启发式优化来设计过量生产聚糖前体的基因敲除菌株。首先,我们将与N-聚糖组装相关的反应纳入N-代谢的基因组规模模型中。然后,我们鉴定了将最佳生长与聚糖合成耦合的基因敲除菌株。模拟表明,这些生长耦合的聚糖过量生产菌株存在代谢失衡,从而使通量重新导向聚糖前体合成。然后,我们通过使用基于流式细胞术的测定法测量聚糖表达,对模型鉴定的敲除菌株进行了实验验证,该测定法涉及对细胞表面展示的聚糖进行荧光标记。总体而言,这项研究证明了代谢建模在优化下一代微生物糖基化平台性能方面可以发挥的有前景的作用。