Dear All, I have a x-ray dataset of a protein-DNA complex to 2.8 A resolution with space group P312 checked by phenix xtriage for twinning. The estimated twin fraction from the output of xtriage is: 0.115 (Britton analysis); 0.119 (H test) and 0.022 (maximum likelihood method). However, the L-test graph in xtriage shows my observed data almost perfectly overlay with theoretical perfect twin data. In addition, when I tried to use phenix to do refinement with twin law -h,-k,l, the log file shows my twin fraction estimation is 0.49, which is very high and much bigger than Britton analysis and H test estimation. As far as my understanding is that if a twin fraction is lower than 15%, I still have hope to solve the structure (molecular replacement in this case) with reasonable R value, but if the twin fraction is 0.49, which is almost a perfect twin, which makes detwin impossible and refinement will stall at high R values (in my case, R free start: 0.4199; R work start: 0.4121; and R free final: 0.4038 and R work final: 0.3640 after running phenix refinement with twin law -h, -k, l). My question: which twin fraction estimation is more reliable? is my data almost perfectly twined? I attached the graphs of L test, Britton analysis and twin estimation from phenix xtriage and part of log file from phenix refine here. Many thanks in advance. Xiao
