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

TL;DR

This study estimates how increasing salt concentration affects the second virial coefficients of E. coli proteins, revealing a significant decrease that impacts protein interactions within the cell.

Contribution

It provides a comprehensive analysis of how salt concentration influences the second virial coefficients of all E. coli proteins based on their charge distribution.

Findings

Second virial coefficients decrease by about twice the average protein volume from 0.2 to 1 M salt.

The decrease in coefficients has a standard deviation comparable to the mean change.

Implications for protein interactions inside E. coli cells are discussed.

Abstract

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. The consequences of this for the complex mixture of proteins inside an E. coli cell, are briefly discussed.