title: Comparison of protein interaction networks reveals species conservation and divergence.
abstract: BACKGROUND
  Recent progresses in high-throughput proteomics have provided us with a first chance to characterize protein interaction networks (PINs), but also raised new challenges in interpreting the accumulating data.
  
  
  RESULTS
  Motivated by the need of analyzing and interpreting the fast-growing data in the field of proteomics, we propose a comparative strategy to carry out global analysis of PINs. We compare two PINs by combining interaction topology and sequence similarity to identify conserved network substructures (CoNSs). Using this approach we perform twenty-one pairwise comparisons among the seven recently available PINs of E.coli, H.pylori, S.cerevisiae, C.elegans, D.melanogaster, M.musculus and H.sapiens. In spite of the incompleteness of data, PIN comparison discloses species conservation at the network level and the identified CoNSs are also functionally conserved and involve in basic cellular functions. We investigate the yeast CoNSs and find that many of them correspond to known complexes. We also find that different species harbor many conserved interaction regions that are topologically identical and these regions can constitute larger interaction regions that are topologically different but similar in framework. Based on the species-to-species difference in CoNSs, we infer potential species divergence. It seems that different species organize orthologs in similar but not necessarily the same topology to achieve similar or the same function. This attributes much to duplication and divergence of genes and their associated interactions. Finally, as the application of CoNSs, we predict 101 protein-protein interactions (PPIs), annotate 339 new protein functions and deduce 170 pairs of orthologs.
  
  
  CONCLUSIONS
  Our result demonstrates that the cross-species comparison strategy we adopt is powerful for the exploration of biological problems from the perspective of networks.
authors.affiliation: Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science & Technology of China, 96 Jinzhai Road, Hefei, Anhui 230027, China. liangzhi968@ustc.edu
authors.forename: Zhi
authors.initials: Z
authors.lastname: Liang
authors.forename: Meng
authors.initials: M
authors.lastname: Xu
authors.forename: Maikun
authors.initials: M
authors.lastname: Teng
authors.forename: Liwen
authors.initials: L
authors.lastname: Niu
mesh_terms: D000818:Animals; D019295:Computational Biology / Q000379:methods; D017124:Conserved Sequence; D053263:Gene Regulatory Networks / Q000502:physiology; D006801:Humans; D025941:Protein Interaction Mapping / Q000379:methods*; D011506:Proteins / Q000737:chemistry* / Q000235:genetics*; D013045:Species Specificity; D015003:Yeasts / Q000235:genetics
chemical_list: D011506:Proteins