Did you check for twinning? The most radical approach is to reprocess
in P1 and see what R-values you get
On Mon, 2011-10-17 at 15:09 -0200, NapoleĆ£o Valadares wrote:
> Hi there!
> I got crystals from some synthetic peptides I bought, they are 30
> residues long and are supposed to form a coiled coil. I collected
> various data sets (home source, Brookhaven and Diamond), including some
> at the resolution of 1.65 A, for which the space group appears to be
> C222 or C2221. The unit cell is small, 22.67, 88.06, 26.13, and the
> Matheus Coefficient indicates that's there's only one helix in the
> asymmetric unit and a 25% solvent content.
>
> I have tried A LOT of Molecular Replacement using Phaser and Phenix
> AutoMR. I'm using a 80% identity coiled coil helix as search model. The
> programs give me solutions with "reasonable" maps, but it is never
> possible to refine to achieve Rvalues below 0.40. Additionally, maps
> from different solutions look reasonable, so I'm thinking these are all
> bias.
>
> I have 5 other synthetic 30 residues peptides (that crystallize in
> different space groups and diffract to lower resolutions), including a
> SelenoMethionine (SM) derivative (but it does not have enough anomalous
> signal, ASU is too big, it is possible that the SM are disordered). I'm
> stuck on this since March.
>
> Regarding the search model, I already tried trimming some or all
> side chains and removing 2, 3 or 5 residues on each/both sides. I also
> tried other search models. Maybe some "magic" combination of parameters
> on Phaser or other programs can help me.
>
> What is your advice regarding how to proceed with MR? Is there some
> program, procedure, parameter, pray or human sacrifice that could help me?
> Thank you.
> Regards,
> Napo
--
Edwin Pozharski, PhD, Assistant Professor
University of Maryland, Baltimore
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When the Way is forgotten duty and justice appear;
Then knowledge and wisdom are born along with hypocrisy.
When harmonious relationships dissolve then respect and devotion arise;
When a nation falls to chaos then loyalty and patriotism are born.
------------------------------ / Lao Tse /
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