The local structural organization of metabolic networks

Metabolic networks share global statistical features. Their connectivity distributions follow a long-tailed power-law and they show the small-world property. In addition, their modular structure is organized in a hierarchical manner. Although the global topological organization of metabolic networks is well understood, local structural organization is still not clear. It is also necessary to understand local properties of metabolic networks for analysis of metabolism. Here, by analyzing subgraphs of metabolic networks of 43 organisms from three domains of life and using the significance profile of subgraphs, we identified the local structural organization of metabolic networks. We identified network motifs, which are statistically significant subgraphs patterns, of metabolic networks. We also showed that metabolic networks from different domains have similar local structure. And we found that local structure of each metabolic network has its own taxonomical meaning. The closer in taxonomy, the more similar local structure. In addition, we found that the common substrates of 43 metabolic networks are not randomly distributed but more likely to be constituents of more cohesive subgraph patterns.