Structure
Antimicrobial peptides are a unique and diverse group of molecules, which are divided into subgroups on the basis of their amino acid composition and structure. Antimicrobial peptides are generally between 12 and 50 amino acids. These peptides include two or more positively charged residues provided by arginine, lysine or, in acidic environments, histidine, and a large proportion (generally >50%) of hydrophobic residues. The secondary structures of these molecules follow 4 themes, including i) α-helical, ii) β-stranded due to the presence of 2 or more disulfide bonds, iii) β-hairpin or loop due to the presence of a single disulfide bond and/or cyclization of the peptide chain, and iv) extended. Many of these peptides are unstructured in free solution, and fold into their final configuration upon partitioning into biological membranes. It contains hydrophilic amino acid residues aligned along one side and hydrophobic amino acid residues aligned along the opposite side of a helical molecule. This amphipathicity of the antimicrobial peptides allows to partition into the membrane lipid bilayer. The ability to associate with membranes is a definitive feature of antimicrobial peptides although membrane permeabilisation is not necessary. These peptides have a variety of antimicrobial activities ranging from membrane permeabilization to action on a range of cytoplasmic targets.
| Type | characteristic | AMPs |
|---|---|---|
| Anionic peptides | rich in glutamic and aspartic acids | Maximin H5 from amphibians, Dermcidin from humans |
| Linear cationic α-helical peptides | lack in cysteine | Cecropins, andropin, moricin, ceratotoxin and melittin from insects, Magainin, dermaseptin, bombinin, brevinin-1,esculentins and buforin II from amphibians, CAP18 from rabbits, LL37 from humans |
| Catioinic peptide enriched for specific amino acid | rich in proline, arginine, phenylalanine, glycine, tryptophan | abaecin, apidaecins from honeybees, prophenin from pigs, indolicidin from cattle. |
| Anionic and cationic peptides that contain cysteine and form disulfide bonds | contain 1~3 disulfide bond | 1 bond:brevinins, 2 bonds:protegrin from pig, tachyplesins from horseshoe crabs, 3 bonds:defensins from humans, more than 3:drosomycin in fruit flies |
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