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Oops George - you are correct.. I guess I never think of using either SIR or SAD phases without some investigation into hand, and then only work with the better result. The selection for SAD is rather straightforward - use SHELXE to do density modification and if your sites are correct it is usually very clear which gives the best result. I dont think anyone now would just do SIR phasing without including the anomalous contribution from the sub-structure as well, and with that extra information you can choose the correct hand. An anomalous difference map with phases from the correct hand shows the anomalous scatterers as strong peaks. Eleanor On Tue, 23 Jul 2019 at 15:03, George Sheldrick <[log in to unmask]> wrote: > I'm afraid that I have to disagree with Eleanor, a very rare event. Both > pure SIR and pure SAD give you only half of the necessary phase > information. The initial map will in both cases be a double image. One then > tries to improve it by density modification. For pure SAD one image is > positive and one is negative, so just setting negative density to zero is a > good start. For pure SIR both images are positive so this does not help, > the map remains centrosymmetric. This also explains why SAD works much > better if the solvent content is high, there is less danger of the images > canceling each other. This is much less of a problem for MAD or SiRAS, both > of which could work for a bromine derivative. If you collected Friedel > opposites you may still be able to try SIRAS. > > George > > > On 23.07.19 11:43, Eleanor Dodson wrote: > > Well - there are lots of ways to proceed. It doesnt really matter for the > crystallography theory if the exptl phases are from SAD or SIR. Just harder > to handle in some software > I think I would start to refine the poor MR model with the xptl phases as > restraints. > REFMAC will do this. Then see if the maps look better - can you see > features not in the model?.. > If they do you could use Buccaneer to try to rebuild the existing model > using exptl phases.. > It might work! > Eleanor > > On Tue, 23 Jul 2019 at 09:55, Luke Smithers < > [log in to unmask]> wrote: > >> Hi all, >> >> I have collected native data and data on a bromide derivative of one of >> my crystals, but have struggled to get a second derivative. I went through >> the SIR pipeline as the anomalous signal from the Br was weak and have >> generated some not-so-great phases. I have also attempted MR with the >> closest match in the PDB (which is only 22% sequence identity) and got some >> more not-so-great phases. I have found plenty of programs that will combine >> SAD/MR phases, is there anything that will do SIR/MR? I understand it's >> likely I will need more and better data and ideally a second derivative but >> thought it was worth putting it out there to see if there is something like >> this. >> >> Luke >> >> -- >> >> *Luke Smithers* >> >> *PhD Candidate* >> >> Protein Production and Structure Facility, School of Molecular Sciences >> >> *T *+61 8 6488 3163 >> >> [image: The University of Western Australia] >> <http://www.uwa.edu.au/university-campaigns-resources/emailsig2015/uwa-logo/> >> >> [image: Pursue Impossible] >> <http://www.uwa.edu.au/university-campaigns-resources/emailsig2015/pursue>[image: >> Facebook] >> <http://www.uwa.edu.au/university-campaigns-resources/emailsig2015/facebook>[image: >> Twitter] >> <http://www.uwa.edu.au/university-campaigns-resources/emailsig2015/twitter>[image: >> Youtube] >> <http://www.uwa.edu.au/university-campaigns-resources/emailsig2015/youtube> >> >> [image: >> http://static.weboffice.uwa.edu.au/visualid/graphics/email/sig2015/campaign.gif] >> <http://www.uwa.edu.au/university-campaigns-resources/emailsig2015/campaign> >> >> >> >> ------------------------------ >> >> To unsubscribe from the CCP4BB list, click the following link: >> https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 >> > > ------------------------------ > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 > > -- > Prof. George M. Sheldrick FRS > Dept. Structural Chemistry > University of Goettingen > Tammannstr. 4 > D37077 Goettingen > Germany > Tel: +49 551 3933021 or +49 5594 227312 > > > ------------------------------ > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 > ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1