Cecropin

Cecropins are a family of linear antimicrobial peptides originally isolated from the hemolymph of the silk moth Hyalophora cecropia. Consisting of 34–39 amino acids, cecropins were among the first insect innate immune peptides characterized. They display broad-spectrum activity against gram-positive and gram-negative bacteria and are templates for synthetic hybrid antimicrobials.

Cecropins adopt an N-terminal amphipathic alpha-helix connected via an Ala-Gly-Pro hinge to a hydrophobic C-terminal helix. The N-terminal helix binds electrostatically to bacterial membrane phospholipids, enabling insertion. At threshold concentrations, cecropins permeabilize bacterial outer and inner membranes through a combination of carpet-model disruption and pore formation. They also inhibit efflux pump activity and interact with intracellular nucleic acids. A conserved N-terminal tryptophan (position 1 or 2) is critical for full antimicrobial activity.

Cecropin A was isolated from H. cecropia in 1980 by Steiner et al. and is one of the founding members of the AMP field. Cecropin B has been extensively studied for its activity against MRSA, E. coli, P. aeruginosa, and biofilms. Cecropin A disrupts uropathogenic E. coli biofilms at sub-MIC concentrations. Hybrid peptides combining cecropin A and melittin (bee venom) N-terminal domains show potent antimicrobial activity with reduced mammalian cell toxicity. Antimalarial activity of Anopheles-derived cecropin-like peptides is under investigation. No cecropin is approved for clinical use.