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