Perhaps the Cys has been oxidized, which would result in sulfenic, sulfinic, or sulfonic acid.
-----Original Message----- From: CCP4 bulletin board on behalf of Cheng, Robert Sent: Thu 7/9/2009 4:05 AM To: [email protected] Subject: [ccp4bb] modified cysteine Hi all I am refining this structure and encountered this extra blob of density on a cysteine residue. It looks like the cysteine has been modified in some way. The density seems very strong (remain visible at 5sigma fofc). I wonder if someone could tell me what modification has taken place. The density would fit a MET residue perfectly but DNA sequence confirms it is a cys. The buffer contains b-mercaptoethanol, PEG, MgAcetate, Tris, Hepes, NaCl and glycerol. Many thanks for your help. Robert Evotec (UK) Ltd is a limited company registered in England and Wales. Registration number:2674265. Registered office: 114 Milton Park, Abingdon, Oxfordshire, OX14 4SA, United Kingdom.
