The coordinates of the X-ray crystal structure of the aromatase/
androstenedione complex (PDB code 3EQM) were downloaded
from the Protein Databank (http://www.rcsb.org) and imported
into the modeling program SYBYL (version 8.0; Tripos, St. Louis,
MO). All non-protein components were deleted and hydrogen
atoms were added to the protein structure. Partial charges were assigned
according to the Amber library and the positions of the
added hydrogen atoms were optimized by molecular mechanics
minimization that kept the positions of the heavy atoms static.42
Energy minimization was performed with the Powell method in
combination with the Amber7 FF99 force field, a distance-dependent
dielectric constant of 4, and a convergence criterion of
0.05 kcal/(mol Å). The molecular structures of inhibitors were also
prepared in SYBYL and the conformational energy of each structure
was minimized by molecular mechanics (MMFF94s force field,
MMFF94 charges, and distance-dependent dielectric constant of
4) using the conjugate gradient method and a termination criterion
of 0.01 kcal/(mol Å).