Erroneous connections in PDB entries. Besides missing connection information, some entries contain surplus connections. (a) In case the wrongly connected atoms are far distant from each other, these errors can be observed on the first view (PDB entry 1qoo, residue NAG401A). In this example, the spuriously assigned connections result in a hexavalent carbon atom. (b) Surplus connections ranging on short distances are much more difficult to discover by visual inspection (PDB entry 1bcs, residues NAG1051, NAG1052).
Lütteke and von der Lieth BMC Bioinformatics 2004 5:69 doi:10.1186/1471-2105-5-69