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PEG likes to hang around where it is unwelcome: http://onlinelibrary.wiley.com/doi/10.1002/pro.2923/full Cheers, Robbie Sent from my Windows 10 phone Van: Bernhard Rupp<mailto:[log in to unmask]> Verzonden: dinsdag 24 januari 2017 23:20 Aan: [log in to unmask]<mailto:[log in to unmask]> Onderwerp: Re: [ccp4bb] Unknown electron density blob Some general remarks about PEG modelling and associated caveats: http://journals.iucr.org/d/issues/2016/12/00/rr5136/index.html Section 3.6.5. Best, BR From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Ana Luísa Moreira de Carvalho Sent: Tuesday, January 24, 2017 10:11 AM To: [log in to unmask] Subject: Re: [ccp4bb] Unknown electron density blob 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 <[log in to unmask]<mailto:[log in to unmask]>> 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" <[log in to unmask]<mailto:[log in to unmask]>> 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://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