Man or mouse? Protein networks highlight differences between organisms
27 May 2008
Research published in the Proceedings of the National Academy of Sciences journal show that the number of protein interactions in a particular organism could reflect its biological complexity.
In the study, scientists found that the network of protein interactions in humans is around ten times bigger than that in fruit flies, and around three times bigger than that in Caenorhabditis elegans, a nematode worm used as model organism in biology.
Scientists had thought that the number of genes in an organism related to its complexity, but the completion of the human and other genome projects showed that this wasn’t the case. The 24 000 or so genes counted in humans was much lower than expected, and not that different from the total number of genes seen in some relatively simple organisms - the fruit fly, for example, has 14 000 genes in total.
“Understanding the human genome definitely does not go far enough to explain what makes us different from more simple creatures. Our study indicates that protein interactions could hold one of the keys to unravelling how one organism is differentiated from another,” says Professor Michael Stumpf, the paper’s primary author and researcher at Imperial College London.
In the study, researchers from Imperial College London worked with colleagues from the Max-Planck-Institute for Molecular Biology in Berlin and the University of Arhus in Denmark to devise a mathematical tool that allowed them to predict the size of an organism’s protein interaction network. This prediction was based on currently available information on protein interactions, which is incomplete.
They estimate that there are around 650 000 interactions in the human ‘interactome’ - the term used to describe the total number of protein interactions in an organism.
In the future it is hoped that careful comparison of the interactomes of closely related species will help researchers understand the different effects of similar organisms - for example,why some fungal species can be used to make bread and beer while others can cause fatal fungal infections.
Image: Partial alignment of protein-protein interaction networks in humans
(bottom) and fruit flies (Drosophila melanogaster; top). The vertical lines depict evolutionary relationships and different colours indicate different protein function; Thomas Thorne
References
Stumpf MP et al. Estimating the size of the human interactome. Proc Natl Acad Sci U S A 2008;105(19):6959-64.