Absent ligands. The active site of hyaluronate lyase from S. agalactiae, PDB entry 1lxm
(Mello et al., 2002), does not contain the electron density needed to justify the presence of the hexasaccharide ligand. (a) shows difference density from the EDS contoured at −2σ, coinciding with the location of the ligand in the deposited model. (b) shows the omit maps and no electron density is observed that would allow ligand placement. (b) shows the 2.2 Å resolution mFo − DFc map contoured at ±3σ (green/red) and 2mFo − DFc maximum-likelihood omit map contoured at 1σ (blue). Maps were calculated for a refined model with the ligand atoms omitted.