You may have crystallized an enzyme that uses a phosphoramidate intermediate.
https://en.wikipedia.org/wiki/Phosphoramidate On Oct 9, 2017, at 10:40 AM, Stephen Cusack <cus...@embl.fr<mailto:cus...@embl.fr>> wrote: Dear All, I am refining the crystal structure of an E. coli expressed protein at 2.65 A resolution. The crystals grew in 0.1 M MES pH6, 0.7 M sodium formate pH 6. Ni-NTA was used in the purification. There are four molecules in the asymmetric unit. A particular histidine in each molecular has clear, strong extra density which looks like a metal bonded to an imidazole nitrogen (distance approx 2 A) with three other co-ordinating atoms in a triangular planar arrangement (see attached screen shot for unbiased extra density, atoms are only put in the density for illustrative purposes). Has anyone seen anything like this ? Any suggestions ? thanks very much Stephen -- ********************************************************************** Dr. Stephen Cusack, FRS Head of Grenoble Outstation of the European Molecular Biology Laboratory (EMBL) Group leader in structural biology of protein-RNA complexes and viral proteins ********************************************************************** Email: cus...@embl.fr<mailto:cus...@embl.fr> Website: http://www.embl.fr Tel: (33) 4 76 20 7238 Secretary (33) 4 76 20 7123 Fax: (33) 4 76 20 7199 Postal address: EMBL Grenoble Outstation, 71 Avenue des Martyrs, CS 90181, 38042 Grenoble Cedex 9, France Delivery address: EMBL Grenoble Outstation, Polygone Scientifique, 71 Avenue des Martyrs, 38000 Grenoble, France ********************************************************************** <Unknown-density.jpg>
