Global topological study of a biological network - the protein-protein interaction network

Abstract

We have employed the combinatory graph theory approach to analyze the protein-protein interacting database, DIP, for five different spe-cies (S. cerevisiae, , H. pylori, H. sapiens, E. coli and M. musculus). Two global topological pa-rameters (connectivity, interaction path length, i.e. diameter) were used to characterize the pro-tein-protein interaction network. Our study indicates that the protein-protein interaction network is neither a random or scale-free net-work The maximum degree of connectivity study seems to indicate that the highly developed species, such as mammal, have a lower degree of connectivity. It is interesting to notice that, the average interaction path length is of the order 2.3 to 6.2 for any two proteins. Furthermore, one can concluded that for all the five species, the interaction network is quite robust when subject to random perturbation, that is the average diameter for the perturbed case are slightly differ from the unperturbed cases. This can be interpreted that the protein-protein interaction network is robust against external perturbations or errors.