alterlab-glycoengineering

Files (3)

• SKILL.md
• evals.json · evals/
• glycan_databases.md · references/

SKILL.md (first lines)

# Glycoengineering

## Overview

Glycosylation is the most common and complex post-translational modification (PTM) of proteins, affecting over 50% of all human proteins. Glycans regulate protein folding, stability, immune recognition, receptor interactions, and pharmacokinetics of therapeutic proteins. Glycoengineering involves rational modification of glycosylation patterns for improved therapeutic efficacy, stability, or immune evasion.

**Two major glycosylation types:**
- **N-glycosylation**: Attached to asparagine (N) in the sequon N-X-[S/T] where X ≠ Proline; occurs in the ER/Golgi
- **O-glycosylation**: Attached to serine (S) or threonine (T); no strict consensus motif; primarily GalNAc initiation

## When to Use This Skill

Use this skill when:

- **Antibody engineering**: Optimize Fc glycosylation for enhanced ADCC, CDC, or reduced immunogenicity
- **Therapeutic protein design**: Identify glycosylation sites that affect half-life, stability, or immunogenicity
- **Vaccine antigen design**: Engineer glycan shields to focus immune responses on conserved epitopes
- **Biosimilar characterization**: Compare glycan patterns between reference and biosimilar
- **Drug target analysis**: Does glycosylation affect target engagement for a receptor?
- **Protein stability**: N-glycans often stabilize proteins; identify sites for stabilizing mutations

### Does NOT Trigger

| Scenario | Use Instead |
|----------|-------------|
| Glycan/carbohydrate cheminformatics (structures, descriptors, SMILES) | `alterlab-rdkit` |
| Identifying glycopeptides from mass-spectrometry raw data | `alterlab-pyopenms` |
| Predicting the 3D structure of the glycoprotein itself | `alterlab-alphafold`, `alterlab-boltz` |
| MD simulation of a glycan shield (setup, force fields, trajectories) | `alterlab-molecular-dynamics` |
| Looking up a protein's curated sequence features in UniProt | `alterlab-uniprot` |

## N-Glycosylation Sequon Analysis

### Scanning for N-Glycosylation Sites

N-glycosylation occurs at the sequon **N-X-[S/T]** where X ≠ Proline.

```python
import re
from typing import List, Tuple

def find_n_glycosylation_sequons(sequence: str) -> List[dict]:
    """
    Scan a protein sequence for canonical N-linked glycosylation sequons.
    Motif: N-X-[S/T], where X ≠ Proline.

    Args:
        sequence: Single-letter amino acid sequence

    Returns:
        List of dicts with position (1-based), motif, and context
    """
    seq = sequence.upper()
    results = []
    # Step by 1, not 3: adjacent sequons can overlap (e.g. NNST has a sequon at
    # both position 1 (N-N-S) and position 2 (N-S-T)); skipping ahead misses them.
    for i in range(len(seq) - 2):
        triplet = seq[i:i+3]
        if triplet[0] == 'N' and triplet[1] != 'P' and triplet[2] in {'S', 'T'}:
            context = seq[max(0, i-3):i+6]  # ±3 residue context
            results.append({
                'position': i + 1,   # 1-based
                'motif': triplet,
                'context': context,
                'sequon_type': 'NXS' if triplet[2] == 'S' else 'NXT'
            })
    return results

def summarize_glycosylation_sites(sequence: str, protein_name: str = "") -> str:
    """Generate a research log summary of N-glycosylation sites."""
    sequons = find_n_glycosylation_sequons(sequence)

    lines = [f"# N-Glycosylation Sequon Analysis: {protein_name or 'Protein'}"]
    lines.append(f"Sequence length: {len(sequence)}")
    lines.append(f"Total N-glycosylation sequons: {len(sequons)}")

    if sequons:
        lines.append(f"\nN-X-S sites: {sum(1 for s in sequons if s['sequon_type'] == 'NXS')}")
        lines.append(f"N-X-T sites: {sum(1 for s in sequons if s['sequon_type'] == 'NXT')}")
        lines.append(f"\nSite details:")
        for s in sequons:
            lines.append(f"  Position {s['position']}: {s['motif']} (context: ...{s['context']}...)")
    else:
        lines.append("No canonical N-glycosylation sequons detected.")

    return "\n".join(lines)

# Example: IgG1 Fc region
fc_sequence = "APELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK"
print(summarize_glycosylation_sites(fc_sequence, "IgG1 Fc"))
```

### Mutating N-Glycosylation Sites

```python
def eliminate_glycosite(sequence: str, position: int, replacement: str = "Q") -> str:
    """
    Eliminate an N-glycosylation site by substituting Asn → Gln (conservative).

    Args:
        sequence: Protein sequence
        position: 1-based position of the Asn to mutate
        replacement: Amino acid to substitute (default Q = Gln; similar size, not glycosylated)

    Returns:
        Mutated sequence
    """
    seq = list(sequence.upper())
    idx = position - 1
    assert seq[idx] == 'N', f"Position {position} is '{seq[idx]}', not 'N'"
    seq[idx] = replacement.upper()
    return ''.join(seq)

def add_glycosite(sequence: str, position: int, flanking_context: str = "S") -> str:
    """
    Introduce an N-glycosylation site by mutating a residue to Asn,
    and ensuring X ≠ Pro and +2 = S/T.

    Args:

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