  The anisotropic feature of charge transfer reactions in realistic proteins
cannot be ignored, due to the highly complex chemical structure of
bio-molecules. In this work, we have performed the first large-scale
quantitative assessment of charge transfer preference in protein complexes by
calculating the charge transfer couplings in all 20*20 possible amino acid side
chain combinations, which are extracted from available high-quality structures
of thousands of protein complexes. The charge transfer database quantitatively
shows distinct features of charge transfer couplings among millions of amino
acid side-chains combinations. The knowledge graph of charge transfer couplings
reveals that only one average or representative structure cannot be regarded as
the typical charge transfer preference in realistic proteins. This data driven
model provides us an alternative route to comprehensively understand the
pairwise charge transfer coupling parameters based structural similarity,
without any require of the knowledge of chemical intuition about the chemical
interactions.
