PEG. It wraps around K or R residues just like you are showing. Artem www.harkerbio.com "where every blob has candy inside"
On Jan 24, 2017 12:19 PM, "Uma Gabale" < 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 >
