The features of low-connectivity essential proteins

Centrality-lethality rule demonstrates high-connectivity proteins in the protein-protein interaction (PPI) network are more likely to be essential than those selected by chance. But the mechanism of centrality-lethality rule is still an intriguing problem in systems biology. There are also many low-connectivity proteins in the PPI network with lethality. In order to explain the reason that low-connectivity proteins are essential, we present three indexes to measure biological features of low-connectivity essential proteins. We compared low-and high-connectivity essential proteins in centrality measures, the appearance in protein complexes, their relationship among neighborhood, functional modularity and so on. Our analysis confirms there are many essential proteins with low-connectivity in PPI networks. They have different properties to high-connectivity essential proteins, which could be used in determining whether the unclassified proteins are essential or not.