[phenixbb] Strong anomalous signal but AutoSol fails

Diana Tomchick Diana.Tomchick at utsouthwestern.edu
Fri Aug 7 09:36:17 PDT 2015

It’s often easiest, when confronted with a case of such high NCS, to use a high resolution limit on the data used for the initial heavy atom search and phasing to 4.0 Angstroms. Does Xtriage indicate translational pseudosymmetry, and do you have systematically weak reflections along one of the reciprocal space axes? If so, it may be possible to process and scale the data in the smaller unit cell, locate the heavy atoms, phase the structure, then use that model for MR into the actual unit cell. See this paper for details:

Li W., Ma C., Guan R., Xu Y., Tomchick D.R., Rizo J. (2011) The crystal structure of a Munc13 C-terminal module exhibits a remarkable similarity to vesicle tethering factors. Structure, 19:1443-1455. PMID: 22000513


Diana R. Tomchick
Departments of Biophysics and Biochemistry
University of Texas Southwestern Medical Center
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Diana.Tomchick at UTSouthwestern.edu
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> On Aug 6, 2015, at 4:16 PM, mohamed noor <mohamed.noor34 at gmail.com> wrote:
> Dear developers
> I have a low resolution anomalous dataset which Aimless suggests has an effective resolution to 3.3 A and anomalous signal to 3.5 A. However, SAD phasing with AutoSol is not successful with the final R factor around 50 %.
> I also have another dataset collected at a remote wavelength without anomalous signal to 3 A but they are not isomorphous (> 2 A difference in c axis).
> The anomalous signal comes from the ligand heme c, which is bound covalently to the protein, so its occupancy should be 1. The protein is quite small with about 120 residues. Xtriage suggests an NCS of 6 to 20 with most likely number to be 13.
> Is there any reason why a reasonable solution cannot be found? There is no twinning.
> I am using the latest nightly 1.10 pre2124.
> Thanks.
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