Partially occupied Cs+ comes to mind. At lower resolution the difference may be
more easily fudged away by the refinement lowering the B.
Mark J van RaaijCNB-CSICwwwuser.csic.es/~mjvanraaij
-------- Original message --------From: Andrew Marshall
<andrew.c.marsh...@adelaide.edu.au> Date: 13/04/2017 07:59 (GMT+01:00) To:
CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] waters with positive FoFc peaks?
Hello all,
I have a 1.8A structure (Rfree/Rwork = 20.5/17.4) with 1420 water molecules
modelled. There are approximately a dozen waters, all well structured with
hydrogen bonds to protein atoms, with positive difference density (>4sigma,
sometimes >5) at their centre. The only ions present in my buffer were Cs, Cl
and a small amount of Na. I thought Cl ions might be a possibility, but many of
them are in close proximity to acidic residues and/or one-another. It's
probably worth noting that the same structure solved using data to 2.25A from
the same crystal at a different wavelength doesn't contain these peaks (the
offending waters look normal).
Has any come across this before? Thoughts?
Thanks,
Andrew MarshallPhD CandidateLaboratory of Protein CrystallographyDept. of
Molecular and Cellular BiologySchool of Biological Sciences
The University of Adelaide
