A 26-amino-acid amphipathic peptide that comprises ~50% of honeybee (Apis mellifera) venom by dry weight. The most studied natural antimicrobial peptide and a model system for understanding how peptides interact with and disrupt cell membranes.
Melittin is a 26-amino-acid peptide and the principal active component of honeybee (Apis mellifera) venom, comprising approximately 50% of dry venom weight. It is one of the most extensively studied antimicrobial peptides (AMPs) in biochemistry, serving as the primary model system for understanding how cationic, amphipathic peptides interact with and disrupt biological membranes.
Melittin's structure is a textbook example of an amphipathic α-helix — when it folds, one face of the helix is hydrophobic (interacts with the lipid membrane interior) while the other face is hydrophilic and positively charged (interacts with the aqueous environment and anionic membrane surface). This dual nature is what gives it its membrane-disrupting ability.
Melittin's mechanism follows the general AMP killing pathway but with unusually high potency. The peptide adopts a random coil structure in solution but transitions to an amphipathic α-helix upon contact with a lipid membrane. The N-terminal 20 residues are predominantly hydrophobic, while the C-terminal 6 residues (KRKRQQ) carry a +5 charge at physiological pH. This charge clustering at the C-terminus is important for initial membrane binding and for the selectivity between bacterial and mammalian cells.
| Pathway | Effect | Significance |
|---|---|---|
| Membrane disruption | Forms pores in lipid bilayers causing uncontrolled ion flux | Direct bactericidal and cytotoxic activity |
| Hemolysis | Disrupts red blood cell membranes at low concentrations | Major limitation for therapeutic use — high toxicity to human cells |
| Anti-cancer | Selectively disrupts cancer cell membranes (more negative than normal cells) | Actively researched for targeted cancer therapy using nanoparticle delivery |
| Anti-inflammatory | Inhibits NF-κB pathway and PLA2 activity | May explain anti-inflammatory effects of bee venom therapy |
| Synergy with antibiotics | Membrane disruption allows conventional antibiotics to enter resistant bacteria | Potential combination therapy to overcome antibiotic resistance |
| Study | Design | Findings | Level |
|---|---|---|---|
| Antimicrobial activity | In vitro, extensive | Broad-spectrum activity against Gram+, Gram−, and fungi. MIC values typically 1-10 μM | Preclinical |
| Cancer research | In vitro + animal models | Selective toxicity to cancer cells, especially when delivered via nanoparticles or conjugated to targeting ligands | Preclinical |
| Bee venom therapy | Clinical observational + small trials | Traditional use for arthritis and pain. Some evidence for anti-inflammatory effects, but controlled trials are limited | Level II-III |
| Anti-HIV | In vitro | Melittin-loaded nanoparticles destroyed HIV viral particles without harming surrounding cells (Washington U study) | Preclinical |
Highly toxic in free form: Melittin causes hemolysis, pain, edema, and can trigger anaphylaxis. It is NOT safe for direct therapeutic injection.
Delivery challenge: The fundamental challenge is delivering melittin to target cells (bacteria, tumors) without destroying healthy tissue. Nanoparticle encapsulation is the primary strategy.
Bee sting allergy: Melittin is a major allergen in bee venom. Anaphylaxis risk in sensitized individuals.
| Jurisdiction | Status |
|---|---|
| FDA | Not approved as a drug. Bee venom is used in some traditional medicine practices but is not FDA-regulated. |
| Research | Actively studied as a lead compound for antimicrobial and anticancer drug development |
| WADA | Not applicable |