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Multiscale guidance of protein structure prediction with heterogeneous cryo-EM data
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Guides the sampling trajectory of a pretrained diffusion structure predictor (Boltz-1) with multiscale global-to-local cryo-EM density guidance to recover multiple conformational states from heterogeneous maps, without retraining.
Problem
Structure prediction models generate ensembles peaked around a single conformation and fail to capture conformational diversity of dynamic biomolecular complexes, while cryo-EM density maps of heterogeneous states lack atomic models and existing model-building tools are incomplete at low resolution.
Approach
Apply DPS-style likelihood guidance to a pretrained AlphaFold3-like diffusion model in atomic space using a two-stage multiscale schedule: a global guidance term matching a weighted k-means point cloud of the map via Sinkhorn divergence, followed by local guidance using a simulated-map likelihood with the original density map, bracketed by unguided warm-up and relaxation steps.
Key results
- On synthetic STP10 inward state, CryoBoltz achieves all-atom RMSD 1.057 Å versus 3.815 Å for Boltz-1 and 1.263 Å for AlphaFold3.
- On four P-glycoprotein states, CryoBoltz reaches all-atom RMSD 1.31–1.73 Å versus 2.93–6.99 Å for Boltz-1, while ModelAngelo completes only 2.3–40.3% of residues.
- On CYP102A1 closed state, guidance improves all-atom RMSD from 8.78 Å (Boltz-1) to 2.00 Å.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| guide Boltz-1 sampling with the matching cryo-EM map | Boltz-1 / CryoBoltz · STP10 inward and outward | all-atom RMSD: 3.815 -> 1.057; 2.656 -> 0.888 | Helped |
| guide Boltz-1 sampling with the matching cryo-EM map | Boltz-1 / CryoBoltz · CH67 antibody | local RMSD: 3.120 -> 1.269 | Helped |
| guide Boltz-1 sampling with the matching cryo-EM map | Boltz-1 / CryoBoltz · P-glycoprotein (apo) | all-atom RMSD: 6.994 -> 1.382 | Helped |
| guide Boltz-1 sampling with the matching cryo-EM map | Boltz-1 / CryoBoltz · Pma1 (inhibited) | all-atom RMSD: 6.140 -> 1.999 | Helped |
| guide Boltz-1 sampling with the matching cryo-EM map | Boltz-1 / CryoBoltz · CYP (closed) | all-atom RMSD: 8.78 Å to 2.00 Å | Helped |
| guide Boltz-1 sampling with the matching cryo-EM map | Boltz-1 / CryoBoltz · CYP (open) | all-atom RMSD: 8.53 Å to 4.17 Å | Helped |
| guide Boltz-1 sampling with the matching cryo-EM map | Boltz-1 / CryoBoltz · YbbAP (bound) | all-atom RMSD: 3.623 -> 1.320 | Helped |
| add global guidance to local-only guidance (ablation) | CryoBoltz · STP10 (inward) | all-atom RMSD: 3.860 -> 1.057 | Helped |
| add local guidance to global-only guidance (ablation) | CryoBoltz · STP10 (inward) | all-atom RMSD: 1.287 -> 1.057 | Helped |
| add global guidance to local-only guidance (ablation) | CryoBoltz · STP10 (outward) | all-atom RMSD: 2.722 -> 0.888 | Helped |
| add local guidance to global-only guidance (ablation) | CryoBoltz · STP10 (outward) | all-atom RMSD: 1.164 -> 0.888 | Helped |
| add local guidance to global-only guidance (ablation) | CryoBoltz · CH67 antibody | all-atom RMSD: 1.281 -> 1.048 | Helped |
Surprising findings
- Unguided AlphaFold3 predicts only the inward STP10 state and Boltz-1 only the outward state, showing single-state bias in both models.
- MSA subsampling of Boltz-1 gives only modest gains and does not sample the alternative STP10 state.
Limitations
- Optimization is unstable due to multimodality of the likelihood; mitigated only by sampling many structures, at higher memory and time cost.
- Relies on the unguided base model providing a good warm-up initialization, which failed on some systems (DSL1/SNARE complex, full IgG antibody).
- Heuristic choices such as stage durations and guidance schedules, and the global point-cloud term, are not physics-derived.
Experimental setup
Datasets: STP10 synthetic map from PDB 7AAQ/7AAR CH67 Fab synthetic map from PDB 4HKX P-glycoprotein EMD-40226/40259/40258/40227 Pma1 EMD-64135/64136 CYP102A1 EMD-27534/27536 YbbAP EMD-51292/51291
Benchmarks: STP10 CH67 antibody P-glycoprotein Pma1 CYP102A1 YbbAP
Metrics: all-atom RMSD C-alpha RMSD TM score local RMSD RSCC
Baselines: Boltz-1 AlphaFold3 Boltz-1 + MSA subsampling ModelAngelo
Builds on: Boltz-1 diffusion posterior sampling (DPS) AlphaFold3 ChimeraX molmap GeomLoss Sinkhorn divergence
Closest papers by meaning
- CryoBench: Diverse and challenging datasets for the heterogeneity problem in cryo-EM (NeurIPS 2024 · similarity 0.92)
- CryoFM: A Flow-based Foundation Model for Cryo-EM Densities (ICLR 2025 · similarity 0.92)
- cryoSPHERE: Single-Particle HEterogeneous REconstruction from cryo EM (ICLR 2025 · similarity 0.92)
- Mixture of neural fields for heterogeneous reconstruction in cryo-EM (NeurIPS 2024 · similarity 0.91)
- Reconstructing Heterogeneous Biomolecules via Hierarchical Gaussian Mixtures and Part Discovery (NeurIPS 2025 · similarity 0.90)
- CryoDomain: Sequence-free Protein Domain Identification from Low-resolution Cryo-EM Density Maps (AAAI 2025 · similarity 0.90)
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