Experimental estimation of proteome size for cells and human plasma

Abstract

Huge range of concentrations of different protein and insufficient sensitivity of methods for detection of proteins at a single molecule level does not yet allow obtaining the whole image of human proteome. In our investigations, we tried to evaluate the size of different proteomes (cells and plasma). The approach used is based on detection of protein spots in 2-DE after staining by protein dyes with different sensitivities. The function representing the dependence of the number of protein spots on sensitivity of protein dyes was generated. Next, by extrapolation of this function curve to theoretical point of the maximum sensitivity (detection of a single smallest polypeptide) it was calculated that a single human cell (HepG2) may contain minimum 70000 proteoforms, and plasma – 1.5 mln. Utilization of this approach to other, smaller proteomes showed the competency of this extrapolation. For instance, the size of mycoplasma (Acholeplasma laidlawii) was estimated in 1100 proteoforms, yeast (Saccharomyces cerevisiae) - 40000, E. coli – 6200, P. furiosus – 3400. In hepatocytes, the amount of proteoforms was the same as in HepG2 – 70000. Significance of obtained data is in possibilities to estimating the proteome organization and planning next steps in its study.