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:

• 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

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:

• URL: https://services.healthtech.dtu.dk/services/NetOGlyc-4.0/
• Input: FASTA protein sequence
• Output: Per-residue O-glycosylation probability scores
• Method: Neural network trained on experimentally verified O-GalNAc sites

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:

• URL: https://gitlab.mpcdf.mpg.de/dioscuri-biophysics/glycoshield-md/
• Use: Map glycan shielding on protein surface over MD trajectory
• Output: Per-residue shielding fraction, visualization

# 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)

• URL: https://www.eurocarbdb.org/project/glycoworkbench
• Use: Draw glycan structures, calculate masses, annotate MS spectra
• Format: GlycoCT, IUPAC condensed glycan notation

4. GlyConnect (Glycan-Protein Database)

• URL: https://glyconnect.expasy.org/
• Use: Find experimentally verified glycoproteins and glycosylation sites
• Query: By protein (UniProt ID), glycan structure, or tissue

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)

• URL: https://unicarbkb.org/
• Use: Browse glycan structures, search by mass or composition
• Format: GlycoCT or IUPAC notation

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

• Start with NetNGlyc/NetOGlyc for computational prediction before experimental validation
• Verify with mass spectrometry: Glycoproteomics (Byonic, Mascot) for site-specific glycan profiling
• Consider site context: Not all predicted sequons are actually glycosylated (accessibility, cell type, protein conformation)
• For antibodies: Fc N297 glycan is critical — always characterize this site first
• Use GlyConnect to check if your protein of interest has experimentally verified glycosylation data

Additional Resources

• GlyTouCan (glycan structure repository): https://glytoucan.org/
• GlyConnect: https://glyconnect.expasy.org/
• CFG Functional Glycomics: http://www.functionalglycomics.org/
• DTU Health Tech servers (NetNGlyc, NetOGlyc): https://services.healthtech.dtu.dk/
• GlycoWorkbench: https://glycoworkbench.software.informer.com/
• Review: Apweiler R et al. (1999) Biochim Biophys Acta. PMID: 10564035
• Therapeutic glycoengineering review: Jefferis R (2009) Nature Reviews Drug Discovery. PMID: 19448661

Glycan Databases and Resources Reference

Primary Databases

GlyTouCan

• URL: https://glytoucan.org/
• Content: Unique accession numbers (GTC IDs) for glycan structures
• Use: Standardized glycan identification across databases
• Format: GlycoCT, WURCS, IUPAC

import requests

def lookup_glytoucan(glytoucan_id: str) -> dict:
    """Fetch glycan details from GlyTouCan."""
    url = f"https://api.glytoucan.org/glycan/{glytoucan_id}"
    response = requests.get(url, headers={"Accept": "application/json"})
    return response.json() if response.ok else {}

GlyConnect

• URL: https://glyconnect.expasy.org/
• Content: Protein glycosylation database with site-specific glycan profiles
• Integration: Links UniProt proteins to experimentally verified glycosylation
• Use: Look up known glycosylation for your target protein

import requests

def get_glycoprotein_info(uniprot_id: str) -> dict:
    """Get glycosylation data for a protein from GlyConnect."""
    base_url = "https://glyconnect.expasy.org/api"
    response = requests.get(f"{base_url}/proteins/uniprot/{uniprot_id}")
    return response.json() if response.ok else {}

def get_glycan_compositions(glyconnect_protein_id: int) -> list:
    """Get all glycan compositions for a GlyConnect protein entry."""
    base_url = "https://glyconnect.expasy.org/api"
    response = requests.get(f"{base_url}/compositions/protein/{glyconnect_protein_id}")
    return response.json().get("data", []) if response.ok else []

UniCarbKB

• URL: https://unicarbkb.org/
• Content: Curated glycan structures with biological context
• Features: Tissue/cell-type specific glycan data, mass spectrometry data

KEGG Glycan

• URL: https://www.genome.jp/kegg/glycan/
• Content: Glycan structures in KEGG format, biosynthesis pathways
• Integration: Links to KEGG PATHWAY maps for glycan biosynthesis

CAZy (Carbohydrate-Active Enzymes)

• URL: http://www.cazy.org/
• Content: Enzymes that build, break, and modify glycans
• Use: Identify enzymes for glycoengineering applications

Prediction Servers

NetNGlyc 1.0

• URL: https://services.healthtech.dtu.dk/services/NetNGlyc-1.0/
• Method: Neural network for N-glycosylation site prediction
• Input: Protein FASTA sequence
• Output: Per-asparagine probability score; threshold ~0.5

NetOGlyc 4.0

• URL: https://services.healthtech.dtu.dk/services/NetOGlyc-4.0/
• Method: Neural network for O-GalNAc glycosylation prediction
• Input: Protein FASTA sequence
• Output: Per-serine/threonine probability; threshold ~0.5

GlycoMine (Machine Learning)

• Machine learning predictor for N-, O- and C-glycosylation
• Multiple glycan types: N-GlcNAc, O-GalNAc, O-GlcNAc, O-Man, O-Fuc, O-Glc, C-Man

SymLink (Glycosylation site & sequon predictor)

• Species-specific N-glycosylation prediction
• More specific than simple sequon scanning

Mass Spectrometry Glycoproteomics Tools

Byonic (Protein Metrics)

• De novo glycopeptide identification from MS2 spectra
• Comprehensive glycan database
• Site-specific glycoform assignment

Mascot Glycan Analysis

• Glycan-specific search parameters
• Common for bottom-up glycoproteomics

GlycoWorkbench

• URL: https://www.eurocarbdb.org/project/glycoworkbench
• Glycan structure drawing and mass calculation
• Annotation of MS/MS spectra with glycan fragment ions

Skyline

• Targeted quantification of glycopeptides
• Integrates with glycan database

Glycan Nomenclature Systems

Oxford Notation (For N-glycans)

Codes complex N-glycans as text strings:

G0F   = Core-fucosylated, biantennary, no galactose
G1F   = Core-fucosylated, one galactose
G2F   = Core-fucosylated, two galactoses
G2FS1 = Core-fucosylated, two galactoses, one sialic acid
G2FS2 = Core-fucosylated, two galactoses, two sialic acids
M5    = High mannose 5 (Man5GlcNAc2)
M9    = High mannose 9 (Man9GlcNAc2)

Symbol Nomenclature for Glycans (SNFG)

Standard colored symbols for publications:

• Blue circle = Glucose
• Green circle = Mannose
• Yellow circle = Galactose
• Blue square = N-Acetylglucosamine
• Yellow square = N-Acetylgalactosamine
• Purple diamond = N-Acetylneuraminic acid (sialic acid)
• Red triangle = Fucose

Therapeutic Glycoproteins and Key Glycosylation Sites

Batch Analysis Example

from glycoengineering_tools import find_n_glycosylation_sequons, predict_o_glycosylation_hotspots
import pandas as pd

def analyze_glycosylation_landscape(sequences_dict: dict) -> pd.DataFrame:
    """
    Batch analysis of glycosylation for multiple proteins.

    Args:
        sequences_dict: {protein_name: sequence}

    Returns:
        DataFrame with glycosylation summary per protein
    """
    results = []
    for name, seq in sequences_dict.items():
        n_sites = find_n_glycosylation_sequons(seq)
        o_sites = predict_o_glycosylation_hotspots(seq)

        results.append({
            'protein': name,
            'length': len(seq),
            'n_glycosites': len(n_sites),
            'o_glyco_hotspots': len(o_sites),
            'n_glyco_density': len(n_sites) / len(seq) * 100,
            'n_glyco_positions': [s['position'] for s in n_sites]
        })

    return pd.DataFrame(results)