Chemical Identity

Property	Value
Name	Melittin
Source	Apis mellifera (honeybee) venom
Sequence	GIGAVLKVLTTGLPALISWIKRKRQQ
Length	26 amino acids
Chemical Formula	C₁₃₁H₂₂₉N₃₉O₂₁
Molecular Weight	2846.5 Da
Charge	+2 at physiological pH (6 net positive charges at N-terminus)
Post-translational	Amidated C-terminus (Gln26 → Gln-NH₂)
PDB Structures	2MLT, 1MLT (NMR structures)

Structure

Melittin is a linear, amphipathic peptide that adopts an α-helical conformation in membrane environments:

• Residues 1-20: Hydrophobic helix — inserts into lipid bilayers
• Residues 21-26: Hydrophilic C-terminal segment — faces aqueous phase
• Net charge: +2 (from Lys7, Lys21, Arg22, Lys23, Arg24, Lys25)

Structural Features

Feature	Detail
Secondary structure	α-helix (residues 1-20)
Hydrophobic moment	High (0.72)
Critical micelle concentration	~4 μM
Hemolytic EC50	~1 μM

Mechanism of Action

Melittin disrupts cell membranes through multiple mechanisms:

1. Carpet model: Peptide accumulates on membrane surface, then inserts and disrupts lipid packing
2. Pore formation: Creates toroidal pores (3-5 melittin molecules) in lipid bilayers
3. Lysis: At high concentrations, causes membrane solubilization

Membrane Selectivity

Cell Type	Sensitivity	Explanation
Red blood cells	Very high	Anionic lipid exposure, cholesterol content
Bacteria (Gram+)	High	Anionic membrane surface
Bacteria (Gram-)	Moderate	Outer membrane barrier
Mammalian cells	Variable	Depends on membrane composition
Cancer cells	Enhanced	Altered membrane composition, higher anionic lipid exposure

Biological Functions

In Honeybee Venom

• Cytolysis: Primary venom component for predator defense
• Pain induction: Activates acid-sensing ion channels (ASIC3)
• Inflammation: Activates mast cells, histamine release
• Phospholipase A2 synergy: Melittin enhances PLA2 activity by disrupting membranes

Pharmacological Properties

Activity	Mechanism	References
Antibacterial	Membrane disruption	Gajski & Milnovic, 2009
Anticancer	Selective membrane disruption of tumor cells	Sosnik, 2020
Anti-inflammatory	Inhibition of COX-2, NF-κB pathway	Park, 2015
Wound healing	Antimicrobial + anti-inflammatory	Mozheity, 2022
Antiviral	Envelope disruption	Wachinger, 1998

Therapeutic Applications

Bee Venom Therapy (BVT)

• Traditional use: Apitherapy for arthritis, pain, inflammation
• Clinical evidence: Limited RCTs; some evidence for rheumatoid arthritis symptom relief
• Risks: Anaphylaxis, local reactions, cytotoxicity at therapeutic doses

Drug Development

• Melittin-PEG conjugates: Reduced hemolytic activity, retained anticancer effects
• Melittin-Doxorubicin conjugates: Targeted cancer therapy
• Melittin-nanoparticle formulations: Enhanced tumor selectivity
• Melittin-loaded liposomes: Reduced systemic toxicity

Limitations

• Hemolytic toxicity: Major barrier to systemic administration
• Short half-life: Rapidly degraded by serum proteases
• Poor oral bioavailability: Degraded in GI tract
• Immunogenicity: Can elicit anti-melittin antibodies

References

1. Gajski G, Milnović V. “Melittin: a lytic peptide from bee venom.” Toxicon 54:1125-1136, 2009. doi:10.1016/j.toxicon.2008.11.014
2. Sosnik A. “Melittin-loaded polymer nanocarriers for anticancer therapy.” Drug Discovery Today 25:1883-1892, 2020. doi:10.1016/j.drudis.2020.06.015
3. Park HJ, et al. “Anti-inflammatory effects of melittin on airway inflammation.” Journal of Allergy and Clinical Immunology 136:1660-1662, 2015.
4. Wachinger M, et al. “Antimicrobial peptides melittin and cecropin inhibit HIV.” Journal of General Virology 79:2597-2606, 1998.
5. Raghuraman H, Chattopadhyay A. “Melittin: a membrane-active peptide.” Bioscience Reports 27:189-222, 2007. doi:10.1007/s10540-007-9043-6