Hi all,
I am dealing with a molecular replacement problem for a 60KDa protein composed of 2 rigid domains joined by a flexible linker which can move relative to each other. Sequence identity for my best model is 46% evenly spread, so in principle this should be a tractable problem. Then the problems start to pile up: a) The unit cell is 56.7Å, 288.5Å, 69.4Å, 90 93.5, 90. Spacegroup P21. Rmerge 12% to 2.4Å. The data also merges relatively well (Rmerge 16%) in P222 with the same a, c and b axes, now of course in that order. In the P21 case, that corresponds to 4 monomers in the asymmetric unit with a solvent content of approx. 50%, giving me 8 domains to find if I separate them. b) The 288 axis means that my data show some overlap in almost all orientations (might be corrected in the future with new datasets), so that my low resolution data are likely unreliable. c) Intensity distributions suggest twinning in either point groups. Actually, they are beyond the perfect twinning case, which I attribute to the reflection overlaps making the strong reflections weaker (integration box too small) and the small stronger (from tails of adjacent strong ones). Of course the latest would mean that the twin fraction estimation is unreliable, but all moments, etc show perfect twin statistics, so I am assuming that there is indeed perfect twinning of some sort. So, the question is, what is the best strategy to deal with this many (4 or 8) body / noisy / twinned problem? I am trying EPMR with many bodies, but I suspect the twinning would throw it out of the right track, and one domain seems to be too little of the diffracting matter to show any sort of discriminations between solutions and non-solutions if do the usual serial searches. I plan to let autotracing programs be the judge of success, but I am not sure of how well those can deal with twinning. Can Arp-Warp use twinned data? Thanks in advance for any tips. Jose. ======================================== Jose Antonio Cuesta-Seijo, PhD Carlsberg Laboratory Gamle Carlsberg Vej 10 DK-1799 Copenhagen V Denmark Tlf +45 3327 5332 Email josea.cuesta.se...@carlsberglab.dk ========================================
