Did you happen to use glycerol as a cryoprotectant? From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> On Behalf Of Daniel Garcia Sent: Monday, 14 May 2018 12:40 PM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] Electron density
Dear all, I am currently refining a structure and found a intriguing electron density at the protein surface (pictures attached, the Fo-Fc map is contoured at >3.5 sigma). My first candidates were molecules from my protein prep or crystallisation buffer, but none of them seem to fit well. I can observe that the ligand is nearby the side chains of a tyrosine, a lysine, a threonine and a glutamate residue, and it is close to the carbonyl oxygens of the protein backbone of a nearby loop. The shape of this density is not pyramidal, but it is not planar either. Do you have any suggestions to solve this density based on your own experience? My crystallisation buffer contains tartrate, ammonium sulphate, and CHES, and my protein is in Tris buffer containing DTT and sodium chloride. Best regards, -- Mario
