Hello, a couple of thoughts. If your best dataset has a twinning fraction of 40% (i.e. almost 50:50 ;-?) and the twin operator corresponds to a 2-fold rotation parallel to the z-axis, is it definitely trigonal, rather than hexagonal? The 2-fold NCS operator that you found for the d3 domains, is it parallel to an axis, e.g. z? Also, how long did the crystals take to grow and do you have the original diffraction images? If so, and I know its hard to tell with fine-slicing on modern detectors, do they look clean or do they show any splitting of the spots, etc? Also, a bit boring question, but when you say the space group is P32, I guess you mean P3 subscript(2) rather than P321, and I take it you have tried alternative space groups in the MR like P3 subscript(1). Are the systematic absences good, or is it all a bit ambiguous?
Best wishes, Jon Cooper. jon.b.coo...@protonmail.com Sent with [ProtonMail](https://protonmail.com) Secure Email. ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Tuesday, 8 September 2020 19:53, Andrew Lovering <a.lover...@bham.ac.uk> wrote: > Dear all, > > I've a project with two historical datasets (i.e. not sure of when/if I can > reproduce to solve problem by getting better data) that are twinned. > > The spacegroup is P32, with operator -h, -k, l > > cell = 83.5 83.5 64.2 90 90 120 > > protein has three domains d1-d2-d3, likely 50% solvent, 2 copies in asu > > dataset 1, roughly 3.6 angstrom resolution, twin fraction 0.25 > > dataset 2, roughly 3.1 angstrom resolution, twin fraction 0.4 > > I've managed to solve this (unambiguously) by finding a d3:d3 dimer in > detwinned data, then seeing via phenix autobuild that it finds a d2 also in > map. At present the ability to interpret the map further stalls there, and it > can't be "the limit" because lack of crystal contacts suggest there should be > more protein to find..... > > I realise I can go two ways, either using the detwinned data or using twinned > data and supplying the operator.....the former giving ridiculously optimistic > R-values with a suspiciously "clean map", the latter giving noisier but maybe > more informative maps. > > Two-fold averaging is not going to be great because the d2-d3 arrangement > observed in monomer 1 clashes when placed over monomer 2 (so at present can > only average the small % of ASU between d3 copies). Critically, looking for a > second d2 using MR fails but the lack of crystal contacts suggests success > should be possible....its really unlikely that a third entity is in there (d1 > and d2 are actually 50% similar, so by searching for d2 and failing, I'm > actually missing three spots it could potentially occupy if the protein is > not proteolysed) > > Sorry for long email but the devil is in the details. My question would be, > what is best practice in a low res poor twinned dataset where you can only > fill roughly just over half of what should be in there? > > Feel free to tell me its doomed! > > Best wishes & thanks in advance > > Andy > > --------------------------------------------------------------- > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 ######################################################################## 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/
