Figure 3.

The PCNA H₁ and I₁β-strands and loop J backbone electrostatic network for 3GPM from PDB_REDO and from the AMOEBA DEE refinement in FFX. The intrastrand interaction is stabilized by five backbone hydrogen bonds in the PDB_REDO structure (above), while the AMOEBA model (below) contains seven. The AMOEBA model has three additional low-energy C_αH···O bonds (purple). The bifurcated hydrogen bonding is driven largely by the quadrupole moment of the carbonyl oxygen. See Fig. S1 for similar improvements in α-helical structure.