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Figure 10
Conformational validation. (a) Chemical errors in the key TM9 sugar, deposited as an N-acetyl α-L-mannosamine derivative (left, PDB entry 4k3t, now superseded by PDB entry 5awv), and their impact on the published structure (right). (b) Correct stereochemistry (left) and re-refined structure after correcting the errors (right). Re-refining the structure with the correct stereochemistry (N-acetyl β-D-glucosamine derivative) causes the sugars to end up in the minimal energy chair conformation. For the stereochemically correct ligand, OMIT density maps (mFoDFc coefficients, contoured at 2σ) show plausible density for the putative diol intermediate at least in chains M and N. While the maps selected by the original authors may not be too different from those obtained through refinement of the correct chemical species at the C6 diol, publishing a distorted sugar with the wrong stereochemistry at almost every position casts legitimate doubt on their glyco-chemical conclusions. This figure was generated with CCP4mg (McNicholas et al., 2011BB65).

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ISSN: 2059-7983
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