Hi Patrick, couldn't see any text in you email, just the subject and the picture, but 2XGF is our T4 long tail fibre tail tip structure from 2010. (2XGF stands for "2nd eXtraordinary Great Fibre", at least that's what I *modestly* imagine..). I think it's probably one or more of: - noise (was this contoured at 3sigma? or at a specific e/Å3 level? at the end of refinements 3sigma corresponds to less e/Å3 than at the start, or at least it should). - perhaps a small percentage of another metal than iron in the site (Co, Ni, Cu, Zn?), it's quite clear most of it was iron though from the X-ray fluorescence spectrum and the fact that the MAD phasing worked - perhaps some radiation damage - ripple effects around the heavy atom sites Resolution was 2.2Å and data was 99.9% complete, multiplicity 3.8, more statistics here: https://www.pnas.org/content/107/47/20287/tab-figures-data <https://www.pnas.org/content/107/47/20287/tab-figures-data> (paper https://www.pnas.org/content/107/47/20287). We didn't consider lowering the occupancy of the irons, or changing from Fe2+ to Fe3+, because that would have meant less electrons, not more as suggested by the positive density. In any case, happy that this thread serves to learn something more from the comments by the experts. Mark
Mark J van Raaij Dpto de Estructura de Macromoleculas Centro Nacional de Biotecnologia - CSIC calle Darwin 3 E-28049 Madrid, Spain Section Editor Acta Crystallographica F https://journals.iucr.org/f/ > On 22 Feb 2021, at 16:16, Patrick Needham <needh...@miamioh.edu> wrote: > > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 > <https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1><Screen > Shot 2021-02-22 at 10.08.36 AM.png> ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/