<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi -<div><br></div><div>I admit I might be preaching the wrong gospel here, but the easiest thing to do in such cases</div><div>is to try Zanuba at the YSBL server. You did most things manually already,</div><div>but giving to that web server the high symmetry data and model,</div><div>it will try systematically all other low symmetry choices and report back. Pretty much what</div><div>you have done but more systematically. Zanuba does not do twin refinement for now.</div><div><br></div><div>btw, I am not 100% confident, but I wonder if the twin fraction in the two out of three</div><div>P21 you are trying is around 50% which could be consistent with a real two fold in that case?</div><div>And the 'real' one less twinned?</div><div><br></div><div>Good luck !</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>A.<br></div><div><br></div><div><div><div>On 26 Nov 2008, at 0:36, HUA YUAN wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Dear Colleagues,<br> <br> I'd like to share with you with a twinning puzzle that's been<br> troubling me for a while.<br> I have a ~2.2 A data merged in p212121 space group with unit cell:<br> 41.8300 117.4490 134.4840 90.0000 90.0000 90.0000<br> Translational NCS was detected but structure solution was able to be<br> obtained by phased molecular replacement as we have a Au derivative<br> data set. Obtaining experimental phase or MR alone didn't work.<br> <br> However, with this model and data set, the refinement didn't work<br> (with R-free ~40% or higher if with more cycles). Different twinning<br> tests have been carried out and no sign of twinning. All possible<br> p222 space groups have been tried but no luck or even worse.<br> Considering that translational symmetry and perfect twinning may make<br> things deceiving, the data was merged into p21 and a twin-refinement<br> was performed in phenix.refine. After 3 cycles of rigid-body and<br> group ADP, a R-free of ~30% was obtained and the output map looks OK.<br> It looks like we got it. But then things get interesting when we<br> tested other two axis as the p21 unique axis. With all the three<br> choices plus corresponding twin-refinement, we could get a similar<br> R-free (30%). Besides, the three maps all look OK except for one<br> missing some side chains.<br> <br> Then the structure was solve in p1 and Xtriage was used with the hope<br> that one axis would stand out. However, the RvsR for all three axis<br> are almost the same. Did I miss anything here? Of course, we could<br> pick up the one axis we like best and get the structure solved ^---^.<br> However, this puzzle would eat me alive for a very long time.<br> <br> Best,<br> <font color="#888888"><br> Hua</font> _______________________________________________<br>phenixbb mailing list<br><a href="mailto:phenixbb@phenix-online.org">phenixbb@phenix-online.org</a><br>http://www.phenix-online.org/mailman/listinfo/phenixbb<br></blockquote></div><br></div></body></html>