Figure 2.

RMSD of electrostatic and polarization energies for neutral oxyluciferin in the (a) aqueous and (b) enzyme environments and anionic oxyluciferin in the (c) aqueous and (d) enzyme environments. All MM charges beyond a cutoff distance were removed from the QM/MM electrostatics calculation in the “Truncation” model, and the long-range electrostatics interaction between these far-field charges and the QM subsystem were described at the MM level in the “Truncation/MMLC” model. Near-field MM charges remained unchanged in the “Step” calculations, but scaled with the long-range electrostatic corrections (“LREC”), “Switch” and “Shift” calculations to ensure a continuous potential energy surface.