Bug in select_primary_ligands_in_df: true ligand coordinates are modified during fragment selection, causing artificially low RMSD

[950288]

There is a bug in select_primary_ligands_in_df (posebench/analysis/inference_analysis.py) that causes the true ligand coordinates (mol_true_frag) to be unintentionally modified during fragment matching. This results in the reference mol_true being aligned to a predicted pose before evaluation, leading to very low RMSD values and overestimated model performance.

Reproduction (example: PDB 1G9V_RQ3)

Added debug prints of Chem.MolToMolBlock(mol_true_frags[0]) before and after this line:

PoseBench/posebench/analysis/inference_analysis.py

Line 173 in b3a15ef

find_most_similar_frag(mol_true_frag, mol_pred_frags)[0]

if row.pdb_id == "1G9V_RQ3":
    print(Chem.MolToMolBlock(mol_true_frags[0]))
mol_pred_frags = [
    find_most_similar_frag(mol_true_frag, mol_pred_frags)[0]
    # find_most_similar_frag(Chem.Mol(mol_true_frag), mol_pred_frags)[0]
    for mol_true_frag in mol_true_frags
]
if row.pdb_id == "1G9V_RQ3":
    print(Chem.MolToMolBlock(mol_true_frags[0]))
    exit()

• Before (original true coordinates):

1G9V_RQ3_A_801
     RDKit          3D

 25 26  0  0  0  0  0  0  0  0999 V2000
   16.1500   22.3350   42.8110 C   0  0  0  0  0  0  0  0  0  0  0  0
   15.3160   21.8930   41.9800 O   0  0  0  0  0  0  0  0  0  0  0  0
   16.9980   23.2070   42.5060 O   0  0  0  0  0  0  0  0  0  0  0  0
   16.1410   21.7710   44.2030 C   0  0  0  0  0  0  0  0  0  0  0  0
   15.1160   22.5540   45.0230 C   0  0  0  0  0  0  0  0  0  0  0  0
   17.5310   21.9290   44.8610 C   0  0  0  0  0  0  0  0  0  0  0  0
   15.7170   20.3840   44.1390 O   0  0  0  0  0  0  0  0  0  0  0  0
   16.5230   19.2430   43.6250 C   0  0  0  0  0  0  0  0  0  0  0  0
   16.2460   17.9700   44.1170 C   0  0  0  0  0  0  0  0  0  0  0  0
   16.9520   16.8770   43.6600 C   0  0  0  0  0  0  0  0  0  0  0  0
   17.9400   17.0290   42.7100 C   0  0  0  0  0  0  0  0  0  0  0  0
   17.5250   19.4050   42.6630 C   0  0  0  0  0  0  0  0  0  0  0  0
   18.2350   18.2860   42.2070 C   0  0  0  0  0  0  0  0  0  0  0  0
   18.6450   15.8760   42.2400 C   0  0  0  0  0  0  0  0  0  0  0  0
   17.8550   15.0410   41.2140 C   0  0  0  0  0  0  0  0  0  0  0  0
   16.7450   15.4130   40.8360 O   0  0  0  0  0  0  0  0  0  0  0  0
   18.2860   13.8040   41.0020 N   0  0  0  0  0  0  0  0  0  0  0  0
   17.7310   12.8920   40.1270 C   0  0  0  0  0  0  0  0  0  0  0  0
   16.3370   12.7960   39.9850 C   0  0  0  0  0  0  0  0  0  0  0  0
   15.7870   11.7440   39.2710 C   0  0  0  0  0  0  0  0  0  0  0  0
   16.6210   10.7910   38.7010 C   0  0  0  0  0  0  0  0  0  0  0  0
   18.5490   11.9350   39.5470 C   0  0  0  0  0  0  0  0  0  0  0  0
   18.0040   10.8950   38.8420 C   0  0  0  0  0  0  0  0  0  0  0  0
   14.3030   11.6400   39.1100 C   0  0  0  0  0  0  0  0  0  0  0  0
   18.9090    9.8760   38.2190 C   0  0  0  0  0  0  0  0  0  0  0  0
  1  2  1  0
  1  3  2  0
  1  4  1  0
  4  5  1  0
  4  6  1  0
  4  7  1  0
  7  8  1  0
  8  9  2  0
  9 10  1  0
 10 11  2  0
  8 12  1  0
 11 13  1  0
 12 13  2  0
 11 14  1  0
 14 15  1  0
 15 16  2  0
 15 17  1  0
 17 18  1  0
 18 19  2  0
 19 20  1  0
 20 21  2  0
 18 22  1  0
 21 23  1  0
 22 23  2  0
 20 24  1  0
 23 25  1  0
M  END

• After (coordinates changed):

1G9V_RQ3_A_801
     RDKit          3D

 25 26  0  0  0  0  0  0  0  0999 V2000
    7.9435   24.1721   34.3343 C   0  0  0  0  0  0  0  0  0  0  0  0
    8.5512   23.6262   35.2904 O   0  0  0  0  0  0  0  0  0  0  0  0
    7.4807   25.3348   34.4147 O   0  0  0  0  0  0  0  0  0  0  0  0
    7.7445   23.3855   33.0704 C   0  0  0  0  0  0  0  0  0  0  0  0
    8.9890   23.5655   32.2015 C   0  0  0  0  0  0  0  0  0  0  0  0
    6.5146   23.9093   32.2937 C   0  0  0  0  0  0  0  0  0  0  0  0
    7.6213   21.9802   33.4129 O   0  0  0  0  0  0  0  0  0  0  0  0
    6.4473   21.3349   34.0619 C   0  0  0  0  0  0  0  0  0  0  0  0
    6.2312   19.9793   33.8276 C   0  0  0  0  0  0  0  0  0  0  0  0
    5.1680   19.3303   34.4195 C   0  0  0  0  0  0  0  0  0  0  0  0
    4.3058   20.0134   35.2512 C   0  0  0  0  0  0  0  0  0  0  0  0
    5.5758   22.0346   34.9025 C   0  0  0  0  0  0  0  0  0  0  0  0
    4.4993   21.3632   35.4978 C   0  0  0  0  0  0  0  0  0  0  0  0
    3.2212   19.3119   35.8667 C   0  0  0  0  0  0  0  0  0  0  0  0
    3.6414   18.4619   37.0812 C   0  0  0  0  0  0  0  0  0  0  0  0
    4.8093   18.4687   37.4675 O   0  0  0  0  0  0  0  0  0  0  0  0
    2.7802   17.5339   37.4788 N   0  0  0  0  0  0  0  0  0  0  0  0
    2.9539   16.6703   38.5416 C   0  0  0  0  0  0  0  0  0  0  0  0
    4.2116   16.1015   38.8012 C   0  0  0  0  0  0  0  0  0  0  0  0
    4.3288   15.0811   39.7307 C   0  0  0  0  0  0  0  0  0  0  0  0
    3.1988   14.6282   40.3989 C   0  0  0  0  0  0  0  0  0  0  0  0
    1.8372   16.2098   39.2215 C   0  0  0  0  0  0  0  0  0  0  0  0
    1.9543   15.2004   40.1397 C   0  0  0  0  0  0  0  0  0  0  0  0
    5.6670   14.4759   40.0170 C   0  0  0  0  0  0  0  0  0  0  0  0
    0.7336   14.7236   40.8665 C   0  0  0  0  0  0  0  0  0  0  0  0
  1  2  1  0
  1  3  2  0
  1  4  1  0
  4  5  1  0
  4  6  1  0
  4  7  1  0
  7  8  1  0
  8  9  2  0
  9 10  1  0
 10 11  2  0
  8 12  1  0
 11 13  1  0
 12 13  2  0
 11 14  1  0
 14 15  1  0
 15 16  2  0
 15 17  1  0
 17 18  1  0
 18 19  2  0
 19 20  1  0
 20 21  2  0
 18 22  1  0
 21 23  1  0
 22 23  2  0
 20 24  1  0
 23 25  1  0
M  END

The topology remains identical, but the coordinate frame is clearly shifted/rotated — meaning mol_true_frag was modified in-place during the call to find_most_similar_frag.

Impact
Downstream RMSD calculations use an already-aligned mol_true, so reported pose accuracy (especially success rate @2Å) is significantly biased high. This affects evaluations on Astex Diverse, PoseBusters, DockGen when select_most_similar_pred_frag=True (default).

Fix
Pass a copy of the true fragment to avoid modifying the original:

find_most_similar_frag(Chem.Mol(mol_true_frag), mol_pred_frags)

(or Chem.Mol(mol_true_frag) inside the function before any RMSD computation)

After applying this fix
On AlphaFold3 (AF3) for Astex Diverse apo docking, the success rate (r.m.s.d. ≤ 2 Å) drops to approximately 60% — a much more realistic value compared to the inflated number before the fix.

Would appreciate if this could be fixed to ensure fair benchmarking. Happy to provide more details or a PR if needed.

Thanks for the great benchmark!

[amorehead]

Hi, @950288.

Thanks for identifying this issue! I'm glad to see you have found the benchmark useful. In my new role, I currently do not have the same computational environment in which I originally ran PoseBench set up. I'd be happy to accept a PR, with the caveat being that we would first need to rerun the (CPU-only) inference_analysis.py part of the inference sweeps for Astex, PoseBusters, and DockGen (3x) and then plot the results.

I can reach out to others to see if they can run these sweeps soon. However, in the meantime, if you happen to run them, I'd be glad to add updated results in a tabular leaderboard (e.g., within the README).

[950288]

Hi, @amorehead.

I’ve now opened a pull request #21 implementing the suggested modification so that the true ligand coordinates are no longer modified during fragment selection.

When convenient, it would be very helpful if the benchmark could be rerun with this patch applied and the updated results shared. That would help clarify how this change affects the reported evaluation metrics.

[amorehead]

Hi, @950288. Thanks for opening this PR. I've reached out to folks for help in rerunning the benchmark. I will let you know once I have more to share.