RESUMO
A package of programs for the examination of areas of subunit contacts (interface) in protein-protein (PP) complexes has been created and used for a detailed study of amino acid (AA) composition and interface structure in a large number of PP complexes from Brookhaven database (PBD). It appeared that in about 75% of the complexes, the AA composition of the subunit surface is not important. This suggests that, along with the surface AA composition, interactions between AA from the inner parts of protein globules may play a significant role in PP recognition. Such interactions between relatively distant AA residues can only be of electrostatic nature and contribute to the total electric field of the protein molecule. The configuration of the electric field itself appears to determine the PP recognition. The total electric field created by protein molecules can be calculated as a result of superimposition of the fields created by the protein multipole (i.e. by the totality of partial electric charges assigned to each atom of the molecule). We performed preliminary calculations for the distant electrostatic interaction of ribonuclease subunits in a vacuum. The results reveal that the effect of the electric fields of the protein multipole is strong enough to orient protein molecules prior to their Brown collision.
