Hi James, I've seen something similar with another metal site. It may be that the X-rays have photoreduced the metal and you may have a different coordination from that seen from the EXAFS data (recorded at much lower dose). A good example is Yano et al. PNAS 102, 12047-12052, X-ray damage to the Mn4Ca complex in single crystals of photosystem II: A case study for metalloprotein crystallography. It's a good example of the problem. Other studies are out there with similar effects send for Fe and Cu.
Cheers, Eddie Edward Snell Ph.D. Assistant Prof. Department of Structural Biology, SUNY Buffalo, Hauptman-Woodward Medical Research Institute 700 Ellicott Street, Buffalo, NY 14203-1102 Phone: (716) 898 8631 Fax: (716) 898 8660 Email: [EMAIL PROTECTED] Telepathy: 42.2 GHz Heisenberg was probably here! Edward Snell Ph.D. Assistant Prof. Department of Structural Biology, SUNY Buffalo, Hauptman-Woodward Medical Research Institute 700 Ellicott Street, Buffalo, NY 14203-1102 Phone: (716) 898 8631 Fax: (716) 898 8660 Email: [EMAIL PROTECTED] Telepathy: 42.2 GHz Heisenberg was probably here! -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of James Pauff Sent: Wednesday, July 11, 2007 9:10 AM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] Metal-ligand(s) positioning following refinement... Good day all, I have a metal center in my enzyme active site, in a roughly square pyramidal coordination. I know from EXAFS and other work how this coordination sphere should look, but following REFMAC the cofactor here does not end up realistically coordinated/oriented. Although it is in the density and roughly in position, the coordination sphere and ligands are not correct, and not correctly connected. Is there a means by which I can position this cofactor, establish the connectivity I want, and then specifically restrain this cofactor/center while refining? Thank you, Jim ________________________________________________________________________ ____________ Need a vacation? Get great deals to amazing places on Yahoo! Travel. http://travel.yahoo.com/
