Hi everyone,

 

I have a data set to 2.8A, with most likely 2 molecules in the asu and a molecular replacement model with 40% sequence identity. (Cell 71.3 71.3 227.9 90 90 90)

 

Initially the data appeared to be either P4322 or P43212 (Rsym = 7.4%; Cell 71.3 71.3 227.9 90 90 90), but the molecular replacement solutions had major clashes with the symmetry related molecules and a lower LLG for the solution of the second molecule. No twinning was detected by Xtriage.

 

Processing the data in P212121 (Rsym 5.6%, cell 71.3 71.4 228.2 90 90 90) gave me a better molecular replacement solution (LLG 121/373), but I had 5 clashes with the second molecule in the asu. (I tested all alternative spacegroups)

 

I also have a MAD dataset (very low quality!) and I combined the phases with the one obtained from molecular replacement in Sharp. After NCS averaging the maps had improved (still not great). I tried to improve things in the model and run Phaser again and the solution had better statistics (LLG 338/1223) and the clashes were reduced to 2.

Xtriage detected pseudo-merohedral twinning with a twin fraction of 43% with twin operator –k, -h, -l.

So I tried refining the model with phenix telling it the twinning operator and fraction, but R/Rfree are stuck around 45%. I also tried simulated annealing but that gave even higher R/Rfree.

 

Is there anything I can do, or is it a hopeless case?

 

Thanks for your help in advance!

 

Sabine