glycoengineering

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:

When to Use This Skill

Use this skill when:

N-Glycosylation Sequon Analysis

Scanning for N-Glycosylation Sites

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

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 = []
    i = 0
    while i <= len(seq) - 3:
        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'
            })
            i += 3
        else:
            i += 1
    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

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:
        position: 1-based position to introduce Asn
        flanking_context: 'S' or 'T' at position+2 (if modification needed)
    """
    seq = list(sequence.upper())
    idx = position - 1

    # Mutate to Asn
    seq[idx] = 'N'

    # Ensure X+1 != Pro (mutate to Ala if needed)
    if idx + 1 < len(seq) and seq[idx + 1] == 'P':
        seq[idx + 1] = 'A'

    # Ensure X+2 = S or T
    if idx + 2 < len(seq) and seq[idx + 2] not in ('S', 'T'):
        seq[idx + 2] = flanking_context

    return ''.join(seq)

O-Glycosylation Analysis

Heuristic O-Glycosylation Hotspot Prediction

def predict_o_glycosylation_hotspots(
    sequence: str,
    window: int = 7,
    min_st_fraction: float = 0.4,
    disallow_proline_next: bool = True
) -> List[dict]:
    """
    Heuristic O-glycosylation hotspot scoring based on local S/T density.
    Not a substitute for NetOGlyc; use as fast baseline.

    Rules:
    - O-GalNAc glycosylation clusters on Ser/Thr-rich segments
    - Flag Ser/Thr residues in windows enriched for S/T
    - Avoid S/T immediately followed by Pro (TP/SP motifs inhibit GalNAc-T)

    Args:
        window: Odd window size for local S/T density
        min_st_fraction: Minimum fraction of S/T in window to flag site
    """
    if window % 2 == 0:
        window = 7
    seq = sequence.upper()
    half = window // 2
    candidates = []

    for i, aa in enumerate(seq):
        if aa not in ('S', 'T'):
            continue
        if disallow_proline_next and i + 1 < len(seq) and seq[i+1] == 'P':
            continue

        start = max(0, i - half)
        end = min(len(seq), i + half + 1)
        segment = seq[start:end]
        st_count = sum(1 for c in segment if c in ('S', 'T'))
        frac = st_count / len(segment)

        if frac >= min_st_fraction:
            candidates.append({
                'position': i + 1,
                'residue': aa,
                'st_fraction': round(frac, 3),
                'window': f"{start+1}-{end}",
                'segment': segment
            })

    return candidates

External Glycoengineering Tools

1. NetOGlyc 4.0 (O-glycosylation prediction)

Web service for high-accuracy O-GalNAc site prediction:

import requests

def submit_netoglycv4(fasta_sequence: str) -> str:
    """
    Submit sequence to NetOGlyc 4.0 web service.
    Returns the job URL for result retrieval.

    Note: This uses the DTU Health Tech web service. Results take ~1-5 min.
    """
    url = "https://services.healthtech.dtu.dk/cgi-bin/webface2.cgi"
    # NetOGlyc submission (parameters may vary with web service version)
    # Recommend using the web interface directly for most use cases
    print("Submit sequence at: https://services.healthtech.dtu.dk/services/NetOGlyc-4.0/")
    return url

# Also: NetNGlyc for N-glycosylation prediction
# URL: https://services.healthtech.dtu.dk/services/NetNGlyc-1.0/

2. GlycoShield-MD (Glycan Shielding Analysis)

GlycoShield-MD analyzes how glycans shield protein surfaces during MD simulations:

# Installation
pip install glycoshield

# Basic usage: analyze glycan shielding from glycosylated protein MD trajectory
glycoshield \
    --topology glycoprotein.pdb \
    --trajectory glycoprotein.xtc \
    --glycan_resnames BGLCNA FUC \
    --output shielding_analysis/

3. GlycoWorkbench (Glycan Structure Drawing/Analysis)

4. GlyConnect (Glycan-Protein Database)

import requests

def query_glyconnect(uniprot_id: str) -> dict:
    """Query GlyConnect for glycosylation data for a protein."""
    url = f"https://glyconnect.expasy.org/api/proteins/uniprot/{uniprot_id}"
    response = requests.get(url, headers={"Accept": "application/json"})
    if response.status_code == 200:
        return response.json()
    return {}

# Example: query EGFR glycosylation
egfr_glyco = query_glyconnect("P00533")

5. UniCarbKB (Glycan Structure Database)

Key Glycoengineering Strategies

For Therapeutic Antibodies

Common Mutations Used

Glycan Notation

IUPAC Condensed Notation (Monosaccharide abbreviations)

Complex N-Glycan Structure

Typical complex biantennary N-glycan:
Neu5Ac-Gal-GlcNAc-Man\
                       Man-GlcNAc-GlcNAc-[Asn]
Neu5Ac-Gal-GlcNAc-Man/
(±Core Fuc at innermost GlcNAc)

Best Practices

Additional Resources