Polder omit map of the HDAC6 CD1–AR-42 complex (PDB 6UO3; inhibitor contoured at 5.0 σ; K330 contoured at 2.5 σ). Atoms are color-coded as follows: C = light blue (monomer A), light gray (symmetry mate), or wheat (inhibitor), N = blue, O = red, Zn2+ = gray sphere, and water molecules = smaller red spheres. Metal coordination and hydrogen bond interactions are indicated by solid and dashed black lines, respectively.