Zipf’s Law in Proteomics

Abstract

Human cells contain many thousands of protein components, protein species/proteoforms, whose cooperation provides the complicated functional mechanisms of the cellular proteome. Though recent methods still do not allow us to obtain the whole picture of this cooperation, they at least provide an opportunity to develop a representation of the proteome size and quantitative distribution of protein species inside the proteome. Using 2DE analysis followed by both protein staining and ESI LC-MS/MS analysis, we performed an analysis of the quantitative distribution of different protein species in human cells. We have analyzed several human cancer cell lines (HepG2, glioblastoma, MCF7) along with the primary liver cells from tissue samples and found that the dependence of the number of protein species on their abundance is described by Zipf’s law: y=ax-1 (1) Where y stands for the number of protein species (N), x stands for the abundance. In the case where the abundance is expressed as %V, and a=14, the final equation is: N=14/%V (2) It is very likely that this type of distribution reflects the fundamental functional organization of the human cellular proteome since it is the same in all types of cells analyzed.