Hi, I would guess radiation damage, see Weik et al., 2000, PNAS 97, 623-628 or for a more recent discussion and thorough overview Sutton et al., 2013, Acta Cryst D69, 2381-2394.
best regards Marjolein On 02 Jun 2014, at 07:08, Eze Chivi <ezech...@outlook.com.ar<mailto:ezech...@outlook.com.ar>> wrote: Hello, when I refine my structure, I see negative density around the disulfide bond. I have 7 copies per ASU, and I can see this density in many of them. In some cases, I see positive density also (negative in the center of the straight line linking S atoms, and positive in both sides). What can I try to solve it? Is it due to radiation damage? Alternative conformation (partial oxidation)? Incorrect disulfide geometry parameters? My resolution is 2.1 A, R/Rfree are around 0.220/0.243, and similar results with refmac5, phenix and PDBREDO. Please find two example pictures in attachment. Thanks for your help! Ezequiel <disulfide.jpg><disulfide2.jpg> [cid:3A2194AC-734C-45EB-B5A7-CE7FC0F0F1BC] Marjolein Thunnissen Science Coordinator MX MAX IV Laboratory Lund University P.O. Box 118, SE-221 00 Lund, Sweden Visiting address: Ole Römers väg 1, 223 63 Lund Telephone: +46 766 32 04 17 www.maxlab.lu.se<http://www.maxlab.lu.se/>
