NegBioDB / src /negbiodb_ppi /models /siamese_cnn.py
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"""SiameseCNN: Shared-weight CNN encoder for PPI binary prediction.
Simple sequence-only baseline. Shared encoder ensures f(A,B) = f(B,A)
symmetry appropriate for PPI (both entities are proteins).
Architecture:
shared_encoder(seq) → emb → Conv1D×3 → AdaptiveMaxPool
[enc(seq1) + enc(seq2), |enc(seq1) - enc(seq2)|] → FC → logit
"""
from __future__ import annotations
import numpy as np
import torch
import torch.nn as nn
# Reuse AA vocabulary from DTI DeepDTA
from negbiodb.models.deepdta import AA_VOCAB_SIZE, _AA_LUT
MAX_SEQ_LEN = 1000 # covers 95%+ of human proteins
def seq_to_tensor(seqs: list[str], max_len: int = MAX_SEQ_LEN) -> torch.Tensor:
"""Encode amino acid sequences to integer tensor (batch × max_len)."""
result = np.zeros((len(seqs), max_len), dtype=np.int64)
for i, seq in enumerate(seqs):
s = seq[:max_len]
codes = np.frombuffer(s.encode("ascii", errors="replace"), dtype=np.uint8)
result[i, : len(codes)] = _AA_LUT[codes]
return torch.frombuffer(result.tobytes(), dtype=torch.int64).reshape(
len(seqs), max_len
).clone()
class _ProteinEncoder(nn.Module):
"""1D-CNN encoder for protein sequences."""
def __init__(
self,
embed_dim: int = 128,
num_filters: tuple[int, int, int] = (64, 96, 128),
kernel_sizes: tuple[int, int, int] = (4, 8, 12),
) -> None:
super().__init__()
self.embed = nn.Embedding(AA_VOCAB_SIZE, embed_dim, padding_idx=0)
layers: list[nn.Module] = []
in_ch = embed_dim
for n_filters, k in zip(num_filters, kernel_sizes):
layers += [nn.Conv1d(in_ch, n_filters, kernel_size=k), nn.ReLU()]
in_ch = n_filters
layers.append(nn.AdaptiveMaxPool1d(1))
self.conv = nn.Sequential(*layers)
self.out_dim = num_filters[-1]
def forward(self, x: torch.Tensor) -> torch.Tensor:
h = self.embed(x).permute(0, 2, 1) # (B, D, L)
h = self.conv(h) # (B, C, 1)
return h.squeeze(-1) # (B, C)
class SiameseCNN(nn.Module):
"""Siamese CNN for PPI binary prediction.
Args:
embed_dim: Embedding dimension for amino acids.
num_filters: Filter counts for 3 conv layers.
kernel_sizes: Kernel sizes for 3 conv layers.
fc_dims: FC layer sizes after concatenation.
dropout: Dropout rate.
"""
def __init__(
self,
embed_dim: int = 128,
num_filters: tuple[int, int, int] = (64, 96, 128),
kernel_sizes: tuple[int, int, int] = (4, 8, 12),
fc_dims: tuple[int, int] = (512, 256),
dropout: float = 0.2,
) -> None:
super().__init__()
# Shared encoder (weight tying → symmetry)
self.encoder = _ProteinEncoder(embed_dim, num_filters, kernel_sizes)
enc_dim = self.encoder.out_dim
# Symmetric aggregation: [enc1 + enc2, |enc1 - enc2|]
concat_dim = enc_dim * 2
fc_layers: list[nn.Module] = []
in_dim = concat_dim
for out_dim in fc_dims:
fc_layers += [nn.Linear(in_dim, out_dim), nn.ReLU(), nn.Dropout(dropout)]
in_dim = out_dim
fc_layers.append(nn.Linear(in_dim, 1))
self.fc = nn.Sequential(*fc_layers)
def forward(
self, seq1_tokens: torch.Tensor, seq2_tokens: torch.Tensor
) -> torch.Tensor:
"""
Args:
seq1_tokens: (B, MAX_SEQ_LEN) integer token ids for protein 1.
seq2_tokens: (B, MAX_SEQ_LEN) integer token ids for protein 2.
Returns:
(B,) raw logits.
"""
e1 = self.encoder(seq1_tokens) # (B, C)
e2 = self.encoder(seq2_tokens) # (B, C)
h = torch.cat([e1 + e2, torch.abs(e1 - e2)], dim=1) # (B, 2C)
return self.fc(h).squeeze(-1) # (B,)