Dear Sam,
to continue from James Parkhurst's email... You can do more analysis regarding ice rings using Auspex (https://www.auspex.de/) if you already have some integrated file. Regarding re-integrating images, what did you use the first time round? I think if you use DIALS it got some clever implementation in it that is better in estimating the errors of reflections in proximity to ice rings. Hence you should get better Rfactors without having to remove the effected resolution range and the data it covers (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5619854/). HTH M ________________________________ From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> on behalf of herman.schreu...@sanofi.com <herman.schreu...@sanofi.com> Sent: 04 April 2019 10:26:09 To: ccp4bb Subject: [ccp4bb] AW: [EXTERNAL] Re: [ccp4bb] High Rfree - ice ring Dear Sam, I would remove the ice ring and reprocess the data. Ice rings may wreak havoc with scaling so at minimum you have to redo the scaling. Best, Herman Von: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] Im Auftrag von Sam Tang Gesendet: Donnerstag, 4. April 2019 11:01 An: CCP4BB@JISCMAIL.AC.UK Betreff: [EXTERNAL] Re: [ccp4bb] High Rfree - ice ring Dear Eleanor and Eric Thanks for your replies. Yes indeed when we looked at the plots e.g. R factor vs resln there was a sharp peak near 3.6 - 3.8 A which is where we visibly saw an ice ring on the image. Thus our first thought was to remove the ic ring. (either reprocess or can we bypass this resolution range during refinement?) The protein is 50 kDa, two molecule in the ASU, seemingly no obvious density was unassigned. We got ~30000 total observations, ~15000 unique observations. NCS restraints was applied. Best regards Sam On Thu, 4 Apr 2019 at 08:57, Eric Montemayor <montemayor.e...@gmail.com<mailto:montemayor.e...@gmail.com>> wrote: That’s a rather large gap between Rwork and Rfree. I suspect you have mis-assigned your space group and as a result have a large number of copies in your asymmetric unit. Any structure can be solved in P1, but that does not mean the true space group is indeed P1. If you use P1 when it’s not actually P1, you will have an unnecessarily overparamerized model, hence the large gap between Rwork and Rfree. Questions: 1- how many copies in your asymmetric unit in P1? 2- how many atoms in your model vs number of unique reflections? 3- if more than one copy per asymmetric unit, are you imposing NCS restraints during refinement? -Eric On Wed, Apr 3, 2019 at 1:41 PM Sam Tang <samtys0...@gmail.com<mailto:samtys0...@gmail.com>> wrote: Hi everyone again Hmmm I think we have solved a structure in P1 space, to 2.5 A. However after refinement the Rfree stuck at 33%-35% with Rwork around 26%. The structure was solved by MR and current model seems to fit density well. In Refmac log I found that at the resolution corresponding to high R there may be a solvent/ice ring. Since imosflm should be able to exclude ice rings, I am not 100% sure whether it's the cause to high R. But if this is actually the case, is there a way I can exclude certain resolution bins during Refmac (and is it an appropriate way to do so?) PS - the data is not affected by twining or pseudosymmetry as checked by Xtriage. Many thanks! 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