> ## Documentation Index
> Fetch the complete documentation index at: https://proto.evodesign.org/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Protein Symmetry Ring Structure
> Constrain protein to form symmetric ring-like multimeric structure
**License:** This constraint can use multiple tools, each under its own license. See the **Tools Used** tab and each tool's page for license details.
This constraint is open source. Any third-party models, product names, or trademarks referenced are the property of their respective owners, and Proto is not affiliated with them.
Constrain proteins to form symmetric ring-like multimeric structures using ESMFold.
This constraint function uses ESMFold to predict multimeric protein
structures and evaluates whether they form symmetric ring-like arrangements.
Ring symmetry is quantified by calculating the centroid (center of mass) of
each protomer's backbone and measuring how uniformly the protomers are
distributed around the ring. Perfect symmetric rings have all inter-protomer
distances equal, resulting in zero standard deviation.
Many functional protein complexes naturally form symmetric rings, including
chaperonins, proteasomes (heptameric rings), hexameric helicases, and various
ring-shaped enzymes. This constraint is useful for designing or selecting
proteins that form such symmetric assemblies.
Each input tuple is folded as one complex with an arbitrary number of protein
chains. DNA chains are first resolved with ORFipy by scanning both strands
for canonical ATG-to-stop ORFs and selecting the longest ORF as that chain's
translated CDS.
Structure prediction is GPU-intensive and may take several minutes per protein
depending on length and hardware.
## API Reference
Configuration for protein symmetry ring constraint.
This class defines configuration parameters for evaluating whether proteins
form symmetric ring-like multimeric structures using ESMFold structure
prediction. Ring symmetry is measured by analyzing the spatial arrangement
of protomer centroids in predicted oligomeric structures. Symmetric rings
have protomers evenly distributed in a circular arrangement with consistent
inter-protomer distances, characteristic of many functional protein complexes
like chaperonins, proteasomes, and ring-shaped enzymes. Symmetry is calculated by
taking the centroids of each protomer (using backbone atom coordinates) and
measuring the standard deviation of distances between protomers. Lower standard
deviation indicates more symmetric arrangements where all protomers are equally spaced.
The score is normalized by dividing by `max_symmetry_std` and capped at 1.0.
Max std of inter-protomer centroid distances (Å) for normalization; above this gets worst score 1.0.
True uses pairwise distances between all protomers. Else, use distances between adjacent protomers
ESMFold configuration for structure prediction.
ReturnsConstraintOutput
Per-proposal score in `[0.0, 1.0]` where 0.0 is
perfect ring symmetry. Protein results attach the predicted `Structure`
to slot 0. `metadata` carries:
* `avg_plddt`: Float average pLDDT score for structure confidence (0.0-1.0)
* `ptm`: Float predicted TM-score for structure accuracy (0.0-1.0)
* `pdb_output`: String PDB format structure file content
* `esmfolded_sequence`: String colon-separated protein-chain representation
* `symmetry_std_raw`: Float raw standard deviation of inter-protomer
distances in Ångströms (lower = more symmetric)
* `symmetry_score_normalized`: Float normalized symmetry score (0.0-1.0)
* `dna_chain_orfs`: Per-DNA-chain ORFipy metadata when DNA chains are present
evo-design/proto-language/proto\_language/constraint/protein\_structure/protein\_symmetry\_ring\_constraint.py
