Detail of PDB entry 1zcs
after automated re-refinement. The carbonyl atoms of Glu20A were modelled with 50% occupancy but without any alternate atom positions by Thapper et al. (2007). This results in a positive mFo − DFc difference-map peak on this carbonyl group, contoured here at 3.0σ. The difference-map peak disappeared after setting the atomic occupancies to 1.00.