The advances in ligand binding affinity prediction have
been fostered
by system generation tools and improved force fields (FFs). CHARMM-GUI Free Energy Calculator provides input and postprocessing
scripts for AMBER-TI free energy calculations with various FFs. In
this study, we used 12 different FF combinations (ff14SB and ff19SB
for protein, GAFF2.2 and OpenFF for ligand, and TIP3P, TIP4PEW, and
OPC for water) to calculate relative binding free energies (ΔΔG
bind) for 80 alchemical transformations (among
the JACS benchmark set) with different numbers of λ windows
(12 or 21) and simulation times (1, 5, or 10 ns). Our results show
that 12 λ windows and 5 ns simulation time for each window are
sufficient to obtain reliable ΔΔG
bind with 4 independent runs for the current benchmark set.
While there is no statistically noticeable performance difference
among 12 different FF combinations compared to the experimental values,
a combination of ff14SB + GAFF2.2 + TIP3P FFs appears to be best with
a mean unsigned error of 0.87 [0.69, 1.07] kcal/mol, a root-mean-square
error of 1.22 [0.94, 1.50] kcal/mol, a Pearson’s correlation
of 0.64 [0.52, 0.76], a Spearman’s correlation of 0.73 [0.58,
0.83], and a Kendell’s correlation of 0.54 [0.42, 0.64]. This
large-scale ΔΔG
bind calculation
study provides useful information about ΔΔG
bind prediction with different AMBER FF combinations and
presents valuable suggestions for FF selection in AMBER-TI ΔΔG
bind calculations.