Hi Liu,
we had a case in our lab where we had one molecule in the ASU even for a swapped dimer, so it is possible to have one molecule in the asymmetric unit even if your protein is a dimer. I would think that your problem might be somewhere else. Did you check with Xtriage if it can flag some issues with the data?
Andrea
On Wednesday, March 25, 2026 07:31 CET, "[email protected]" wrote:
Dear PhenixBB community,
I am currently working on solving the structure of protein X (110 amino acids). The protein forms a dimer in solution, and dimerization is functionally relevant.
Based on initial analysis, the asymmetric unit (ASU) was estimated to contain one copy [unit cell: 82.699, 82.699, 36.435, 90 , 90, 120]. The data extend to 1.2 Å resolution, but the final R factors are around 0.23/0.25, which seem higher than expected at this resolution, and we have not been able to improve them further.
When I examined the structure using symmetry mates in PyMOL, I observed a clear dimer that appears biologically meaningful. This makes me suspect that the ASU estimation might be incorrect—especially for a small protein like this, the ASU could potentially contain a dimer rather than a monomer.
However, every time I use a dimer model as the search model for molecular replacement, Phaser consistently returns a monomer solution. I would greatly appreciate any suggestions on how to successfully obtain the dimeric model that matches the crystallographic symmetry.
Thank you in advance for your help!
Best regards,
Liu
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