Cecropin A
Cecropin A is a 37-amino acid antimicrobial peptide from the giant silk moth Hyalophora cecropia, the first insect AMP discovered, with potent activity against gram-negative bacteria.
Chemical Identity
| Property | Value |
|---|---|
| Chemical Formula | C175H303N47O53 |
| Molecular Weight | 4003.68 g/mol |
| CAS Number | 80451-04-3 |
| IUPAC Name | Cecropin A (Hyalophora cecropia) |
| Peptide Class | Insect Antimicrobial Peptide |
| Origin | Hyalophora cecropia (giant silk moth) |
Structure
Cecropin A is a 37-amino acid linear, cationic, amphipathic alpha-helical peptide. It was the first antimicrobial peptide isolated from an insect by Hans Boman’s group in 1981. The peptide has two amphipathic helical regions connected by a flexible hinge at residues 14-16 (Gly-Pro). The N-terminal helix (residues 1-13) is highly basic, while the C-terminal helix (residues 17-37) is more hydrophobic. This amphipathic structure is essential for membrane disruption.
Mechanism of Action
Cecropin A kills bacteria through membrane disruption:
- Electrostatic attraction: The cationic N-terminal domain binds to anionic bacterial membrane lipids
- Helix insertion: The amphipathic helix inserts parallel to the membrane surface
- Pore formation: Above a threshold concentration, the peptide forms voltage-dependent ion channels
- Membrane permeabilization: Ion leakage leads to loss of membrane potential and cell death
Cecropin A shows selectivity for bacterial membranes over mammalian cell membranes, with minimal hemolytic activity at antimicrobial concentrations.
Biological Functions
Cecropin A is part of the humoral immune response in insects:
- Induction: Synthesized in the fat body and hemocytes in response to bacterial infection
- Spectrum: Primarily active against gram-negative bacteria (E. coli, P. aeruginosa) with moderate activity against some gram-positive species
- Synergy: Works synergistically with attacins, lysozyme, and other insect immune effectors
- Expression: Induced via the Toll and Imd signaling pathways
Clinical Relevance
Cecropin A inspired the development of numerous synthetic AMPs and established the amphipathic alpha-helix as a key structural motif in antimicrobial peptides. Synthetic cecropin-melittin hybrids (e.g., cecropin A-melittin CA(1-7)M(2-9)) show enhanced potency. These peptides are under investigation for wound healing, food preservation, and anti-infective coatings. No cecropin-based therapeutics have reached market yet.
Safety and Side Effects
Cecropin A has low toxicity to mammalian cells at antimicrobial concentrations. Minimal hemolytic activity (typically <2% at 100 microM). Rapidly degraded by serum proteases, limiting systemic applications. The D-amino acid substitution strategy has been used to improve metabolic stability while maintaining antimicrobial activity.
References
- Steiner, H., et al. (1981). Sequence and specificity of two antibacterial proteins involved in insect immunity. Nature, 292, 246-248.
- Boman, H.G. (1995). Peptide antibiotics and their role in innate immunity. Annual Review of Immunology, 13, 61-92.
Test Your Knowledge
Reinforce what you learned about Cecropin A with interactive quizzes on Wikipept.
Take a Quiz on Wikipept