We are refining a 2.7 A structure with multiple ASN-NAG links using phenix-1.3-final. The torsion angle between the Asn amide and the sugar is quite variable, while from the chemistry of this link we would expect a value close to 180°, as reported in the PDB survey by Imberty & Perez (Protein Engineering 8:669-709). A quick look at some entries in the PDB revealed close to textbook geometry for the NAG-ASN link in structures around 1Å resolution (e.g. 1UWC) and gets much worse in some lower resolution structures, including those refined with PHENIX. The NAG-ASN link used by PHENIX does not contain a torsion angle definition, and I would like to ask (i) if its appropriate to use one in refinement, and if so (2) could people share their cif file for this link. Thanks - MLM