What is role of isoelectric point in protein protein interactions?
The answer is that at its isoelectric point the protein surface carries no net charge. As protein solubility is based upon favourable electrostatic interactions between the charges (negative or positive) on the protein surface and the delta-negative or delta-positive dipoles on water molecules, when there is LEAST charge on the protein surface you can also expect their to be the least favourable interactions between water molecules and the protein. As the protein-water interaction is in competition with protein-protein interactions, being at the pI most favours protein-protein interactions, which leads to precipitation, compared to protein-water interaction which lead to solvation.
