Hello Tiantian
since there don't seem to be any replies to your message, I can suggest looking
at the following points:
1) What is the unit cell and space group? Is there any scope for misindexing or
twinning problems?
2) You have several heavy atom datasets, so why do you want to solve it with
SAD? There may be isomorphous signal there which should be stronger.
3) Do you have the figures of merit and phasing power for the individual
derivatives? Also, do the sites have good occupancies after refinement?
4) Are the derivatives all indexed consistently and are the sites of the
different derivatives all on a common hand and origin? This is handled
correctly by solve/resolve on the phenix side of things, and I guess the Crank
pipeline, but we used to do it by cross-phased Fouriers.
That's all that springs to mind for now. Hope some of it helps.
Jon.C.
On Thursday, 25 April 2019, 16:05:23 BST, ChenTiantian
<[email protected]> wrote:
Dear all,
I'm working on a 18kD protein, the secondary structure prediction says most of
the structure is beta sheets, trying to solve the structure with SAD.Heavy atom
soaking gives several datasets with I, W, Au, range from 2.7~3.7A, however, the
anomalous signal is pretty weak, I couldn't find a reasonable solution.We got a
co-crystal dataset with the magic triangle I3C, extends to around 2.5A, this is
the best data we got so far.shelxc gives me the following result:
Resl. Inf. 12.59 7.75 5.84 4.77 4.08 3.59 3.22 2.94 2.70 2.51 2.35
N(data) 79 257 429 635 811 1010 1235 1384 1698 1555 1954
Chi-sq 0.69 0.63 0.60 0.67 0.61 0.88 1.05 1.02 0.80 0.55 0.42
<I/sig> 79.4 34.1 30.3 32.2 31.8 26.6 21.1 14.6 8.3 3.9 2.4
%Complete 94.0 98.1 97.5 99.5 99.4 99.0 99.7 100.0 99.9 85.4 96.1
Multipl. 4.0 4.5 3.9 4.5 4.7 4.2 4.4 4.8 5.0 4.3 4.4
R(pim)% 2.27 1.72 2.29 2.05 2.02 2.62 3.51 4.84 7.90 14.43 22.78
Ranom% 6.49 3.68 5.19 4.29 4.27 6.35 9.50 12.97 20.90 33.58 52.21
<d"/sig> 0.73 0.80 1.08 0.85 0.95 1.03 1.00 0.91 0.85 0.78 0.70
CC(1/2) 5.1 41.7 68.8 38.1 42.7 49.9 49.9 25.5 24.9 13.3 -4.7
then I tried shelxd with different heavy atom sites number and resolution cut,
the best CC I got is CC/CCweak: 24.75/7.69,
and I can identify a triangle, (length: 6.5/6.5/5.0A), however, both shelxe and
autosol didn't end up with a promising result.
It would be great if anyone can give me some suggestions.
Thank you in advance!--
Tiantian
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