Zipf’s Law in Proteomics

After completion of the human genome sequencing and determination of its size, there is a great demand for similar information about the human proteome as proteins mediate almost all processes in a cell. To better understand the functionality of proteins, we need the information about their activity that is directly linked to their abundance. However, the situation is not simple here because of the complexity of proteins themselves. This complexity may arise from allelicvariations, alternative splicing of RNA transcripts, and post-translational modifications. All these cellular events create distinct protein molecules, proteoforms/protein species, that modulate a wide variety of biological processes. 

Apparently, by using standard technologies, it has been impossible so far to identify and calculate all protein species/ proteoforms present in a single human cell or in human plasma. The main problem is a huge dynamic range of concentrations, where the number of copies of different protein species in an object lies in the range from one to a billion molecules. One ofquantitative proteomic approaches, a proteomic technique that is mainlyperformed using 2DE or liquid chromatography-tandem mass spectrometry (LC-MS/MS) is expected to offer an alternative solution this problem. Recently, using a shotgun approach, a large amount of information about protein abundance was produced. This information is still not enough as we still need to know how many specific molecules (protein species/ proteoforms) are present in a cell.