Dear Kai,
You may try to use the SHELIXIR pipeline developed by Petr Kolenko which
runs SHELX C/D/E with numerous parameters to find a strategy which would
work.
https://kmlinux.fjfi.cvut.cz/~kolenpe1/shelixir
In any case, as was pointed out in the previous responses, it's
important to understand all the aspects to perform the experiment
carefully and provide a valid input to the software programs. And any
case which cannot be solved nowadays using molecular replacement of an
AlphaFold prediction is interesting!
Good luck!
Martin
On 11/07/2026 12:40, [email protected] wrote:
Dear all,
I am currently processing a SAD dataset collected from a Se-Met
derivative. According to the |matthews_coef| calculation in CCP4,
there should be 20 heavy atom sites in the asymmetric unit.
However, due to the very weak anomalous signal, the occupancy
refinement in SHELX shows only one site with an occupancy above 1.0,
one site around 0.4, and the remaining 15 sites all converging to
approximately 0.3.
Given this situation, I would be very grateful for any suggestions on
how to obtain reliable initial phases. Are there any specific
strategies, software settings, or alternative approaches (e.g.,
density modification or partial structure refinement) that you would
recommend to make the most of this weak signal?
Thank you in advance for your time and insights.
Best regards,
Kai Zhang
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