Discovering functional interaction patterns in protein-protein interaction networks

Mehmet E Turanalp¹ and Tolga Can²

¹Department of Computer Engineering, Selcuk University, Alaaddin Keykubat Kampusu, 42075 Selcuklu, Konya, Turkey

²Department of Computer Engineering, Middle East Technical University, Inonu Bulvari, 06531 Cankaya, Ankara, Turkey

author email corresponding author email

BMC Bioinformatics 2008, 9:276doi:10.1186/1471-2105-9-276


Published:	11 June 2008

Abstract

Background

In recent years, a considerable amount of research effort has been directed to the analysis of biological networks with the availability of genome-scale networks of genes and/or proteins of an increasing number of organisms. A protein-protein interaction (PPI) network is a particular biological network which represents physical interactions between pairs of proteins of an organism. Major research on PPI networks has focused on understanding the topological organization of PPI networks, evolution of PPI networks and identification of conserved subnetworks across different species, discovery of modules of interaction, use of PPI networks for functional annotation of uncharacterized proteins, and improvement of the accuracy of currently available networks.

Results

In this article, we map known functional annotations of proteins onto a PPI network in order to identify frequently occurring interaction patterns in the functional space. We propose a new frequent pattern identification technique, PPISpan, adapted specifically for PPI networks from a well-known frequent subgraph identification method, gSpan. Existing module discovery techniques either look for specific clique-like highly interacting protein clusters or linear paths of interaction. However, our goal is different; instead of single clusters or pathways, we look for recurring functional interaction patterns in arbitrary topologies. We have applied PPISpan on PPI networks of Saccharomyces cerevisiae and identified a number of frequently occurring functional interaction patterns.

Conclusion

With the help of PPISpan, recurring functional interaction patterns in an organism's PPI network can be identified. Such an analysis offers a new perspective on the modular organization of PPI networks. The complete list of identified functional interaction patterns is available at http://bioserver.ceng.metu.edu.tr/PPISpan/ webcite.