549 research outputs found
Graph theoretic analysis of protein interaction networks of eukaryotes
Thanks to recent progress in high-throughput experimental techniques, the
datasets of large-scale protein interactions of prototypical multicellular
species, the nematode worm Caenorhabditis elegans and the fruit fly Drosophila
melanogaster, have been assayed. The datasets are obtained mainly by using the
yeast hybrid method, which contains false-positive and false-negative
simultaneously. Accordingly, while it is desirable to test such datasets
through further wet experiments, here we invoke recent developed network theory
to test such high throughput datasets in a simple way. Based on the fact that
the key biological processes indispensable to maintaining life are universal
across eukaryotic species, and the comparison of structural properties of the
protein interaction networks (PINs) of the two species with those of the yeast
PIN, we find that while the worm and the yeast PIN datasets exhibit similar
structural properties, the current fly dataset, though most comprehensively
screened ever, does not reflect generic structural properties correctly as it
is. The modularity is suppressed and the connectivity correlation is lacking.
Addition of interlogs to the current fly dataset increases the modularity and
enhances the occurrence of triangular motifs as well. The connectivity
correlation function of the fly, however, remains distinct under such interlogs
addition, for which we present a possible scenario through an in silico
modeling.Comment: 7 pages, 6 figures, 2 table
The evolutionary dynamics of the Saccharomyces cerevisiae protein interaction network after duplication
Gene duplication is an important mechanism in the evolution of protein interaction networks. Duplications are followed by the gain and loss of interactions, rewiring the network at some unknown rate. Because rewiring is likely to change the distribution of network motifs within the duplicated interaction set, it should be possible to study network rewiring by tracking the evolution of these motifs. We have developed a mathematical framework that, together with duplication data from comparative genomic and proteomic studies, allows us to infer the connectivity of the preduplication network and the changes in connectivity over time. We focused on the whole-genome duplication (WGD) event in Saccharomyces cerevisiae. The model allowed us to predict the frequency of intergene interaction before WGD and the post duplication probabilities of interaction gain and loss. We find that the predicted frequency of self-interactions in the preduplication network is significantly higher than that observed in today's network. This could suggest a structural difference between the modern and ancestral networks, preferential addition or retention of interactions between ohnologs, or selective pressure to preserve duplicates of self-interacting proteins
IsoRankN: spectral methods for global alignment of multiple protein networks
Motivation: With the increasing availability of large protein–protein interaction networks, the question of protein network alignment is becoming central to systems biology. Network alignment is further delineated into two sub-problems: local alignment, to find small conserved motifs across networks, and global alignment, which attempts to find a best mapping between all nodes of the two networks. In this article, our aim is to improve upon existing global alignment results. Better network alignment will enable, among other things, more accurate identification of functional orthologs across species.
Results: We introduce IsoRankN (IsoRank-Nibble) a global multiple-network alignment tool based on spectral clustering on the induced graph of pairwise alignment scores. IsoRankN outperforms existing algorithms for global network alignment in coverage and consistency on multiple alignments of the five available eukaryotic networks. Being based on spectral methods, IsoRankN is both error tolerant and computationally efficient.National Science Council of Taiwan (NSC-096-2917-I- 002-114)National Science Council of Taiwan (NSC-095-2221-E-001-016-MY3)Fannie and John Hertz Foundatio
Infinite-Order Percolation and Giant Fluctuations in a Protein Interaction Network
We investigate a model protein interaction network whose links represent
interactions between individual proteins. This network evolves by the
functional duplication of proteins, supplemented by random link addition to
account for mutations. When link addition is dominant, an infinite-order
percolation transition arises as a function of the addition rate. In the
opposite limit of high duplication rate, the network exhibits giant structural
fluctuations in different realizations. For biologically-relevant growth rates,
the node degree distribution has an algebraic tail with a peculiar rate
dependence for the associated exponent.Comment: 4 pages, 2 figures, 2 column revtex format, to be submitted to PRL 1;
reference added and minor rewording of the first paragraph; Title change and
major reorganization (but no result changes) in response to referee comments;
to be published in PR
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