Dear Rhys, an important addendum to the magic triangle is the fact that it gives you direct evidence whether or not the substructure search has succeeded (by locating the triangle in the substructure solution) so that you can carry on with phasing via density modification. At 3.5A resolution this is an utterly time- and effort saving piece of information you do not want to miss.
Best, Tim On 01/15/2014 07:21 PM, Tanner, John J. wrote: > More references to consider… > > You asked about soaking times - here are two articles advocating quick > soaking at relatively high heavy atom concentration, which has worked well > for us. We've had good luck with thimerosal. > > Acta Crystallogr D Biol Crystallogr. 2002 Jul;58(Pt 7):1099-103. Epub 2002 > Jun 20. > Generating isomorphous heavy-atom derivatives by a quick-soak method. Part > II: phasing of new structures. > Sun PD, Radaev S. > > Acta Crystallogr D Biol Crystallogr. 2002 Jul;58(Pt 7):1092-8. Epub 2002 Jun > 20. > Generating isomorphous heavy-atom derivatives by a quick-soak method. Part I: > test cases. > Sun PD, Radaev S, Kattah M. > > Petsko has a good discussion about the chemistry of heavy atom derivatization. > > Methods Enzymol. 1985;114:147-56. > Preparation of isomorphous heavy-atom derivatives. > Petsko GA. > PMID: 4079763 > > Beck et al. would suggest you consider the triiodo magic triangle. > > Acta Cryst. (2008). D64, 1179-1182 [ doi:10.1107/S0907444908030266 ] > A magic triangle for experimental phasing of macromolecules > T. Beck, A. Krasauskas, T. Gruene and G. M. Sheldrick > > > > > > John J. Tanner > Professor of Biochemistry and Chemistry > University of Missouri-Columbia > 125 Chemistry Building > Columbia, MO 65211 > Phone: 573-884-1280 > Fax: 573-882-2754 > Email: tanne...@missouri.edu<mailto:tanne...@missouri.edu> > http://faculty.missouri.edu/~tannerjj/tannergroup/tanner.html > > On Jan 15, 2014, at 11:32 AM, Engin Özkan > <eoz...@stanford.edu<mailto:eoz...@stanford.edu>> > wrote: > > There is quite a bit of literature on this, but my favorite paper is this: > > http://www.ncbi.nlm.nih.gov/pubmed/18391402 > Towards a rational approach for heavy-atom derivative screening in protein > crystallography. > > Spoiler: The overall winner is ethyl mercury phosphate (Figure 7). Of course, > chemistry will dictate your success (as every article and book chapter on > this topic stresses). Check out quick soak literature, but not halides like > sodium bromide (less likely to work at your resolution). > > Engin > > On 1/15/14, 11:18 AM, RHYS GRINTER wrote: > Hello message board, > > My group has some crystals of an interesting protein to take to the > synchrotron in a couple of weeks. We won't be able to prepare and crystallise > a SelMet derivative during that time period, but we have loads of crystals > sitting around. The diffraction isn't great, we see maybe 3.5 at home but > might be enough to get over the line. > It will be a very difficult MR target, so we were thinking of soaking so > crystals with heavy atomic compounds that we have lying around. I was > wondering if people had any suggestions of compounds that people have used > successfully for experimental phasing and maybe concentrations to use and > soaking time. > > Cheers, > > Rhys > > -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A
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