OHE of the AAs was used for the 20 AAs, which, adding one slot for unknown AAs (X, Z, or B), produced 21 node features. Four physical AA descriptors were taken from the literature: hydrophobicity , volume , and alpha-helix and beta-sheet propensities . Four new physical descriptors were calculated for this investigation: ionization energy (IE), electron affinity (EA), dipole moment and polarizability; see details below. All physical descriptors were normalized before use as node features, and mean values were used for unknown AAs.