Peptide Properties Calculation

Usage

1. MCP Server Definition

Use the same BiologyToolsClient class as defined in the protein-properties-calculation skill.

2. Peptide Properties Calculation Workflow

This workflow calculates comprehensive physicochemical properties of peptide sequences for peptide drug design, synthesis planning, and characterization.

Workflow Steps:

1. Calculate Peptide Properties - Compute MW, pI, extinction coefficient, GRAVY, and chemical formula
2. Analyze Multiple Peptides - Compare properties across different sequences

Implementation:

## Initialize client
HEADERS = {"SCP-HUB-API-KEY": "<your-api-key>"}

client = BiologyToolsClient(
    "https://scp.intern-ai.org.cn/api/v1/mcp/29/SciToolAgent-Bio",
    HEADERS
)

if not await client.connect():
    print("connection failed")
    exit()

print("=== Peptide Properties Calculation ===\n")

## Input: Peptide sequences to analyze
peptides = [
    ("All 20 amino acids", "ACDEFGHIKLMNPQRSTVWY"),
    ("Glycine repeat", "GGGGG"),
    ("Arginine repeat (positively charged)", "RRRRR"),
]

## Calculate properties for each peptide
for name, peptide in peptides:
    print(f"--- {name}: {peptide} ---")

    # Calculate peptide properties
    result = await client.client.call_tool(
        "CalculatorPeptideProperty",
        arguments={
            "sq": peptide,
            "aaCode": "0",          # Use single-letter code
            "nTerm": "",            # N-terminal modification (if any)
            "cTerm": "",            # C-terminal modification (if any)
            "disulphideBonds": ""   # Disulfide bonds (if any)
        }
    )
    result_data = client.parse_result(result)
    print(f"{result_data}\n")

## Additional analysis: Peptide weight calculation
print("=== Peptide Weight Calculation (Alternative Method) ===\n")
test_peptide = "ACDEFGHIKLMNPQRSTVWY"

result = await client.client.call_tool(
    "PeptideWeightCalculator",
    arguments={"sequence": test_peptide}
)
result_data = client.parse_result(result)
print(f"Peptide: {test_peptide}")
print(f"{result_data}\n")

## Additional analysis: Peptide formula calculation
print("=== Peptide Chemical Formula ===\n")

result = await client.client.call_tool(
    "PeptideFormulaCalculator",
    arguments={"sequence": test_peptide}
)
result_data = client.parse_result(result)
print(f"Peptide: {test_peptide}")
print(f"{result_data}\n")

await client.disconnect()

Tool Descriptions

SciToolAgent-Bio Server:

• CalculatorPeptideProperty: Calculate comprehensive peptide properties

  • Args:
    • sq (str): Peptide sequence (single or three-letter code)
    • aaCode (str): "0" for single-letter, "1" for three-letter code
    • nTerm (str): N-terminal modification (e.g., "Acetyl", "")
    • cTerm (str): C-terminal modification (e.g., "Amide", "")
    • disulphideBonds (str): Disulfide bonds specification
  • Returns: MW, extinction coefficient, pI, GRAVY, chemical formula, sequence length

• PeptideWeightCalculator: Calculate peptide molecular weight

  • Args: sequence (str) - Peptide sequence
  • Returns: Molecular weight in Daltons

• PeptideFormulaCalculator: Calculate peptide chemical formula

  • Args: sequence (str) - Peptide sequence
  • Returns: Molecular formula (e.g., C₁₀₇H₁₅₉N₂₉O₃₀S₂)

Input/Output

Input:

• sq: Peptide sequence in single-letter (ACDEFG...) or three-letter (Ala-Cys-Asp...) code
• aaCode: "0" for single-letter code, "1" for three-letter code
• nTerm: Optional N-terminal modification
• cTerm: Optional C-terminal modification
• disulphideBonds: Optional disulfide bond specification

Output:

• Average Molecular Weight: Mass in g/mol or Daltons
• Extinction Coefficient: For peptide quantification at 280nm (M⁻¹cm⁻¹)
• Theoretical Isoelectric Point (pI): pH at which peptide has no net charge
• GRAVY (Grand Average of Hydropathy): Hydrophobicity index
• Chemical Formula: Elemental composition (C, H, N, O, S)
• Sequence Length: Number of amino acid residues
• Three-letter Representation: Full peptide notation

Use Cases

• Design peptide drugs and therapeutics
• Plan peptide synthesis strategies
• Calculate peptide concentrations spectrophotometrically
• Predict peptide solubility and stability
• Optimize peptide purification conditions
• Design peptide-based biosensors
• Analyze peptide fragments from mass spectrometry

Terminal Modifications

Common N-terminal modifications:

• Acetyl: Blocks N-terminus, increases stability
• Formyl: Common in bacterial proteins
• None: Free amine group (default)

Common C-terminal modifications:

• Amide: Blocks C-terminus, increases stability
• None: Free carboxyl group (default)

Example with modifications:

result = await client.client.call_tool(
    "CalculatorPeptideProperty",
    arguments={
        "sq": "ACDEFG",
        "aaCode": "0",
        "nTerm": "Acetyl",
        "cTerm": "Amide",
        "disulphideBonds": ""
    }
)

GRAVY Interpretation

• GRAVY < -0.5: Very hydrophilic (highly soluble)
• GRAVY -0.5 to 0: Hydrophilic (soluble)
• GRAVY 0 to +0.5: Hydrophobic (may have solubility issues)
• GRAVY > +0.5: Very hydrophobic (likely membrane-associated or poorly soluble)

Extinction Coefficient Usage

Calculate peptide concentration:

Concentration (M) = Absorbance at 280nm / (Extinction Coefficient × Path Length)

Where path length is typically 1 cm for standard cuvettes.

Note: Extinction coefficient is primarily determined by Trp (5500), Tyr (1490), and Cys-Cys (125) residues.

Additional Peptide Tools Available

• ConvertingPeptide2SMILES: Convert peptide sequence to SMILES notation
• ProteinIsoelectricPointCalculator: Calculate pI for longer sequences
• ComputeAffinity: Predict peptide-protein binding affinity
• OverlapPeptideLibraryDesign: Design peptide libraries
• AlanineScanningLibraryDesign: Design mutagenesis libraries
• TruncationLibraryDesign: Design truncation variants