Hi Rohit, If it is of some significance you may consider replacing NaCl with KI or NaI in your crystallization condition and collect a dataset at 1.5-2 Angstrom. The Iodide anomalous signal might be of some help for identifying Chloride binding sites. Without further evidence for a Cl ion, unless the environment strongly suggests an anion binding site (as what Robbie said) my personal view is that it is more proper to put a water there.
Zhijie From: rohit kumar Sent: Tuesday, January 20, 2015 1:59 AM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] chloride or water Dear all, I am solving a data of 3.0 Å resolution. In the active site we found an unidentified blob. The crystallization condition is (PEG 3350-25%, Naformate-200mM, MES (100mM)-6.5pH, and Nacl-200mM). Can anyone suggest what it could be? If I suppose that, it is chloride, how could someone differentiate between a chloride moiety and water. below I am showing the coot figure in two different orientations. Thanks in advance... -- WITH REGARDS Rohit Kumar Singh Lab. no. 430, P.I. Dr. S. Gourinath, School of Life Sciences, Jawaharlal Nehru University New Delhi -110067
