Hi, I have a very peculiar crystal structure which has been challenging to solve:
Prot-X + VHH – nominally expected to be a 1:1 complex Data auto-process as C2 CRYST1 132.084 56.245 86.262 90.00 108.40 90.00 C 1 2 1 2 copies of Prot-X easily located by molecular replacement, Phaser fails to find the VHH Manual assessment of density in crystal voids reveals a density patch about the right size / shape for a VHH. Manual placement of a VHH into this density shows it lies across the C2 2-fold so the lattice symmetry places an inverted copy of the placed VHH in the same location. Expanding the symmetry to P1 gives 4-chains, arranged in a square ring, with a hole in the middle where the VHH sits, sterically only 1 VHH can sit in the hole CRYST1 56.245 71.780 86.262 106.88 90.00 113.07 P 1 I overlaid a computational model of Prot-X + VHH onto each of the 4 chains, 2 positions align reasonably with the density (related by 2-fold as expected), the other 2 do not. If I refine either of these models in P1 with twin refinement then I get a reasonable map, especially where the VHH contacts Prot-X as the alternative 2-fold related position does not overlap at the contact surface. Some parts of the density look really good, some are a bit confused / look like some rebuilding is required, though this may be largely residual density from the alternate orientation. Data resolution is modest with fairly noisy outer shell data so I can process to 2.6A with much better stats in C2 but only 2.8A and significantly worse stats in P1. I have had similar cases before in monoclinic/orthorhombic and trigonal/hexagonal and was able to obtain better maps by symmetry expanding the higher resolution processing from the higher symmetry spacegroup to the lower symmetry spacegroup rather than processing in the lower symmetry. I would therefore like to take the C2 processed data, symmetry expand to P1 and then use these expanded data for twin refinement to try and improve map quality. I am however not sure how to expand / transform the data from the C2 lattice to the P1 case. Help appreciated… Thanks, Charlie. ######################################################################## 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/
