Graph summarization for finding relations of protein functions

Recent technologies give us comprehensive protein-protein interactions (PPI). Most of the PPI network analysis methods focus on local interaction structures [1, 2]. In this study, to understand the global regulation of cellular functions within the PPI network, we introduce the summarization method of the large PPI network under the restriction of both network relationships and homogeneity of known protein functions. For the extract of the structure, we propose an optimization problem by introducing a new index which measures attributes homogeneity in a group and relations between two groups. By applying the method to a yeast PPI network, we find network motifs associated with regulations of start time of cell functions and generation of cell energies and discover that the cell cycle proteins can be categorized into two different groups.