代谢网络交替最优和近似最优流量分布中高流量骨干的守恒性
Conservation of high-flux backbone in alternate optimal and near-optimal flux distributions of metabolic networks
摘要：
基于约束的通量平衡分析（FBA）已被证明在预测不同环境条件下代谢网络的通量分布方面是成功的。FBA找到使生物质生产率最大化的备选最优解之一。Almaas等人已经表明，通量分布遵循幂律，并且可能与大多数代谢物相关的两个反应分别最大限度地产生和消耗给定代谢物。这一观察结果导致了代谢网络中高通量骨架（HFB）的概念。在以前的工作中，HFB已经使用通过FBA获得的特定最优值进行了计算。本文研究了在给定的培养基下，E. coli和革兰氏阳性菌S.啤酒。使用通量变异性分析（FVA），我们提出了一种方法来确定反应，保证在HFB，而不考虑替代解决方案。我们发现，在E. coli中，而在S.啤酒。然而，在两种生物体中，特定的近最佳状态的HFB在交替的近最佳状态之间显示出较大的变化。我们证明了HFB中的保守反应集与本质反应和唯一消耗（UC）和唯一产生（UP）的反应有很大的重叠.我们的研究结果表明，代谢网络的结构在接近最佳的流动模式中具有高度的冗余性和可塑性，从而增强了系统在给定环境条件下的鲁棒性。
英文摘要：
Constraint-based flux balance analysis (FBA) has proven successful in predicting the flux distribution of metabolic networks in diverse environmental conditions. FBA finds one of the alternate optimal solutions that maximizes the biomass production rate. Almaas et al have shown that the flux distribution follows a power law, and it is possible to associate with most metabolites two reactions which maximally produce and consume a give metabolite, respectively. This observation led to the concept of high-flux backbone (HFB) in metabolic networks. In previous work, the HFB has been computed using a particular optima obtained using FBA. In this paper, we investigate the conservation of HFB of a particular solution for a given medium across different alternate optima and near-optima in metabolic networks of E. coli and S. cerevisiae. Using flux variability analysis (FVA), we propose a method to determine reactions that are guaranteed to be in HFB regardless of alternate solutions. We find that the HFB of a particular optima is largely conserved across alternate optima in E. coli, while it is only moderately conserved in S. cerevisiae. However, the HFB of a particular near-optima shows a large variation across alternate near-optima in both organisms. We show that the conserved set of reactions in HFB across alternate near-optima has a large overlap with essential reactions and reactions which are both uniquely consuming (UC) and uniquely producing (UP). Our findings suggest that the structure of the metabolic network admits a high degree of redundancy and plasticity in near-optimal flow patterns enhancing system robustness for a given environmental condition.
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