Just to add to this, in our group, we had a funny case where we found PEG around K:
https://drive.google.com/open?id=0B2DrnhrLgvwGSldLVl9pSEptakE https://drive.google.com/open?id=0B2DrnhrLgvwGZlNiYTFoaktPUHc Ana Luisa > On 24 Jan 2017, at 17:36, Artem Evdokimov <artem.evdoki...@gmail.com> wrote: > > PEG. It wraps around K or R residues just like you are showing. > > Artem > www.harkerbio.com <http://www.harkerbio.com/> > "where every blob has candy inside" > > On Jan 24, 2017 12:19 PM, "Uma Gabale" > <00000ebb5dcf3eaa-dmarc-requ...@jiscmail.ac.uk > <mailto:00000ebb5dcf3eaa-dmarc-requ...@jiscmail.ac.uk>> wrote: > Dear all, > While refining a structure at 2.5 A resolution, we observed a > semi-circular/crescent shaped electron density blob as shown in the attached > picture. We have been unable to identify it so far, and would appreciate any > help in identification. > The protein was expressed in E. coli BL21(DE3), purified on Ni-NTA followed > by gel filtration. The purification buffers included Tris and NaCl (no > detergent/ other ingredients except for imidazole for Ni-NTA). > Crystallization condition had HEPES and PEG3350; no cryoprotectant was used. > The blob is surrounded by residues Trp, Thr, Gln, Arg, and Phe. > Thanks and regards, > Uma. > > -- > Uma Gabale, PhD > Research Associate > Molecular and Cellular Biochemistry > Indiana University Bloomington Research Assistant Professor at UCIBIO@REQUIMTE-FCT-NOVA *************************************************************************** Biologia Estrutural - Cristalografia de Raios-X (Gab 6.34) Dep. Quimica, FCT-UNL 2829-516 Caparica Portugal Phone: 00351212948300 (ext: Gab: 10940; Lab: 10962; X-ray Lab: 10915) Fax: 00351212948550 http://docentes.fct.unl.pt/almc <http://docentes.fct.unl.pt/almc> http://sites.fct.unl.pt/xtal https://www.facebook.com/XtalNOVA/ *************************************************************************** Single Crystal X-ray Structure Determination Service: http://www.dq.fct.unl.pt/en/single-crystal-x-ray-structure-determination
