The effects of added salt on the second virial coefficients of the complete proteome of E. coli

Bacteria typically have a few thousand different proteins. The number of proteins with a given charge is a roughly Gaussian function of charge — centred near zero, and with a width around ten (in units of the charge on the proton). We have used the charges on E. coli’s proteins to estimate the changes in the second virial coefficients of all its proteins as the concentration of a 1:1 salt is increased. The second virial coefficient has dimensions of volume and we find that on average it decreases by about twice the average volume of a protein when the salt concentration is increased from 0.2 to 1 Molar. The standard deviation of the decrease is of the same order. Such information on a large set of proteins is important for structural genomics, the large scale determination of protein structures.