Topological properties of protein interaction network and phylogenetic age of proteins

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Proteins interact with each other to regulate their functionality and localization. The accumulated protein interaction evidences are represented by protein interaction network using a graph abstraction. Topological properties of protein interaction networks have been explored to characterize proteins and predict undiscovered interactions. Meanwhile, many researchers have tried to explain how protein interaction network is formed through evolutionary process. While one group of researchers have made efforts to simulate current protein interaction starting from hypothetical infant state of protein interaction networks through suggested evolutionary models, another group of researchers have made efforts to estimate the phylogenetic age of proteins from evolutionary relationship. Recently, these efforts gave rise to the database of phylogenetic age of proteins and this allows many researchers to estimate phylogenetic age of proteins of their interest easily. As seen by their terms, the evolutionary model of protein interaction networks and phylogenetic age of proteins are closely related, thus topological properties of protein interactions, which is important in studies of the evolutionary models, can be linked to the phylogenetic age of proteins. In this paper, we construct a weighted human protein interaction network from a human protein interaction network, which is provided by BioGRID database. The weight of an edge is defined as the number of triangles which contains this edge in the protein interaction network and we call this weight as the triangle score. From the weighted protein interaction network, we extract proteins that are incident to an edge that has a high triangle score. We obtain phylogenetic age of proteins and measure various statistical values to observe correlation between phylogenetic age and the triangle score. As a result, we show that the proteins, that participate in interactions with high triangle score, are old in terms of phylogenetic age. Also we show that for interactions within a same phylogenetic age category tend to have higher triangle scores than the interactions with only one of its participant protein contained in the given age category.