Call EBI, consider some kind of chemical modification. FF Dr Felix Frolow Professor of Structural Biology and Biotechnology, Department of Molecular Microbiology and Biotechnology Tel Aviv University 69978, Israel
Acta Crystallographica F, co-editor e-mail: mbfro...@post.tau.ac.il Tel: ++972-3640-8723 Fax: ++972-3640-9407 Cellular: 0547 459 608 On Apr 25, 2013, at 19:10 , Antony Oliver <antony.oli...@sussex.ac.uk> wrote: > Dear CCP4 colleagues. > > I'm just finishing up a refinement, but am left with one little curio that I > just can't seem to solve. > > One aspartic acid residue is associated with some extra, unexplained electron > density. > > --> please see: http://i.imgur.com/vCYOqam.png > > Where, the Fo-Fc map is contoured at 3.78 rsmd in Coot. > > I have tried a number of different modelling scenarios, but as yet can't > reach a wholly satisfactory conclusion; waters, alternate conformers, really > don't seem to cut it. I though about some radiation-induced phenomena, but > this data set was collected on a home-source, so I guess this is unlikely. > > So, I would really appreciate some ideas and suggestions. Hopefully it is > blindingly obvious to someone. > > Random Thought: could it be PEGylation of the side-chain? > > Some other hopefully useful background information: > > * I'm sure it is/was an ASP, because the same protein (made from the same > construct) has been used in previous crystallisations, and the resultant > structures have clear, unambiguous electron density for the side chain. > > * the crystallization condition is PEG 200, with some Na/K phosphate at pH > 5.8, and NaCl. The protein itself contains HEPES buffer. > > With many thanks, > > Tony. > > --- > Dr Antony W Oliver > Senior Research Fellow > CR-UK DNA Repair Enzymes Group > Genome Damage and Stability Centre > Science Park Road > University of Sussex > Falmer, Brighton, BN1 9RQ > > email: antony.oli...@sussex.ac.uk > tel (office): +44 (0)1273 678349 > tel (lab): +44 (0)1273 677512
