---
library_name: sentence-transformers
tags:
- sentence-transformers
- protein
- esm-c
- contrastive-learning
- protein-embeddings
- biology
license: mit
language:
- en
pipeline_tag: sentence-similarity
datasets:
- fredzzp/afdbseq
- OATML-Markslab/ProteinGym_v1
- Synthyra/StringDBSeqsv12
base_model:
- biohub/ESMC-300M
---

# ProtSent-V2 ESM-C 300M

Contrastively fine-tuned [ESM-C 300M](https://huggingface.co/Synthyra/ESMplusplus_small)
producing fixed-length protein embeddings where biological similarity maps to embedding
proximity. Intended for retrieval, clustering, and nearest-neighbour transfer.

This is the ProtSent V2 recipe applied to an ESM-C backbone. 
Continued training from the  `Synthyra/ESMplusplus_small` (ESMC-300M) weights.

## Usage

```python
from sentence_transformers import SentenceTransformer
from sentence_transformers.util import cos_sim

model = SentenceTransformer("GrimSqueaker/ProtSent-V2-ESMC-300M", trust_remote_code=True)
emb = model.encode([
    "MKTLLLTLVVVTIVCLDLGYT",
    "MKTLLLTLVVVTIVCLDLGYN",
    "AGWYRSPQEGLKPVDTFKDIV",
])
print(cos_sim(emb[0], emb[1:]))
```

Embeddings are mean-pooled over the final layer, dimension 960. No Matryoshka heads on
this release (see Training configuration).

## Training data

Four sources. Pfam/AFDB/STRING are decontaminated against benchmark test sets (see
below); the DMS source is not — see Limitations.

| source | pairs used |
|---|---:|
| Pfam families | 1,230,551 |
| AlphaFold DB (Foldseek clusters) | 27,105,179 |
| STRING-DB v12 PPI | 15,000,000 |
| ProteinGym DMS (CoSENT target) | 1,000,000 |
| **total** | **44,335,730** |

Pfam/AFDB pairs are drawn with the disjoint-pair sampler at up to 10 pairs per cluster
(`k=10`), which spends the pair budget on distinct sequence pairs rather than repeating
members — covers up to 90 distinct sequences per cluster instead of 10. STRING is a fixed
15M-pair subsample (seed 42).

## Decontamination

Pfam, AlphaFold DB and STRING were searched against the benchmark test sequences with
MMseqs2 `easy-search` (40% identity, 80% coverage, `--cov-mode 1`) and matching sequences
removed before training — the same `protsent-data-dc40` corpus used by the ProtSent-V2.5
ESM-2 releases.


## Training configuration

| setting | value |
|---|---|
| backbone | ESM-C 300M (`Synthyra/ESMplusplus_small`, 960 hidden) |
| loss | CachedMultipleNegativesRankingLoss (Pfam/AFDB/STRING) + CoSENT (DMS) |
| contrastive batch | 2048 per device |
| gather across devices | off |
| multi-dataset sampler | proportional, world-size-aligned (see below) |
| GOR weight | 0 (off) |
| Matryoshka | off |
| max sequence length | 512 |
| optimiser | AdamW, LR 1e-4, warmup 300 steps |
| precision / attention | bf16, flash-attention-2 (FA3 unavailable on this hardware) |
| hardware | 3x NVIDIA B300 |
| steps | 7,216 (one epoch) |
| gradient-cache mini-batch | 128 |

Training code: [github.com/oriel9p/ProtSent](https://github.com/oriel9p/ProtSent),
`train_esmc_300m_v2.sh`.


## Results

23-task suite, `-e test`, seed 42, both kNN and linear-probe transfer. Full per-task CSVs:
`results/benchmarks/ism/protsent_esmc_300m_v2_{knn,linear}/` in the repo above.

### SCOPe-40 structural retrieval, eligible queries only

| method | R@1 | R@10 | MAP |
|---|---:|---:|---:|
| ESM-C 300M (this model's backbone, untrained) | 0.3709 | 0.5794 | 0.2212 |
| ISM-C 300M (structure-distilled ESM-C 300M) | 0.4300 | 0.6592 | 0.2733 |
| HMMER (phmmer, filters off) | 0.7525 | 0.8978 | 0.6067 |
| **ProtSent-V2 ESM-C 300M** | **0.7974** | **0.9539** | **0.7692** |


### 23-task suite vs the model's own untrained backbone and vs ISM-C

Win/tie/loss, tie tolerance 0.005:

| probe | vs ESM-C 300M (this backbone, untrained) | vs ISM-C 300M |
|---|---|---|
| kNN | 16W / 0T / 7L | 14W / 1T / 8L |
| linear | 6W / 3T / 14L | 6W / 4T / 13L |



## Citation

Paper: [ProtSent: Protein Sentence Transformers](https://doi.org/10.48550/arXiv.2605.06830)