Classification of antimicrobial peptides.
| Class | Peptide name | Source organisms | Mechanism | References |
|---|---|---|---|---|
| α-Helical peptides | Magainins, LL-37, cecropins | Amphibians (frog skin), humans, insects | Unstructured in solution; adopts α-helical conformation upon membrane contact; amphipathic; disrupts membranes via pore formation (barrel stave/toroidal models). | [17] |
| β-Sheet peptides | Defensins (α-, β-defensins), tachyplesins | Mammals, plants, and horseshoe crabs | Stabilized by disulfide bonds; rigid structures; strong membrane binding; pore-forming activity. | [18] |
| Extended/unstructured peptides | Indolicidin, Bac5, Bac7 | Cattle, insects | Rich in specific amino acids (proline, tryptophan, glycine); flexible structure; can penetrate cells; target DNA, RNA, or ribosomes. | [19] |
| Cyclic peptides | Theta-defensins, Lantibiotics (nisin) | Primates (rare), bacteria | Backbone/head to tail cyclization; high stability against proteolysis; potent against Gram-positive bacteria; often inhibit cell wall biosynthesis. | [20] |
| Lipopeptides | Daptomycin, polymyxin B, surfactin | Bacteria (e.g., Streptomyces, Bacillus) | Peptides conjugated with lipid tail; insert into bacterial membranes; disrupt integrity; clinically used as last resort antibiotics. | [21] |
| Mammalian peptides | Cathelicidins (LL-37), defensins | Humans, cattle, other mammals | Crucial in innate immunity; immunomodulatory roles; involved in wound healing and inflammation regulation. | [22] |
| Amphibian peptides | Magainins, dermaseptins, esculentins | Frogs, toads | Rich source of diverse antimicrobial peptides (AMPs); mostly α-helical; highly potent against bacteria and fungi. | [23] |
| Insect peptides | Cecropins, attacins, defensins, melittin | Moths, flies, bees | Defense peptides secreted in hemolymph; active against Gram-negative bacteria and fungi; some (melittin) are cytolytic. | [24] |
| Plant peptides | Thionins, plant defensins, cyclotides | Wheat, barley, medicinal plants | Contribute to pathogen resistance; many are cysteine-rich; cyclic variants are highly stable. | [25] |
| Microbial peptides (bacteriocins) | Nisin, subtilin, pediocin | Gram-positive bacteria (e.g., Lactococcus, Bacillus) | Ribosomally synthesized; potent, narrow or broad-spectrum antibacterial activity; widely used in food preservation. | [26] |
| Membrane-targeting | Cecropins, magainins, LL-37 | Insects, amphibians, humans | Disrupt membranes by pore formation (barrel stave, toroidal, carpet models); rapid killing. | [27] |
| Non-membrane-targeting | Indolicidin, buforin II, Bac7 | Cattle, frogs, insects | Inhibit nucleic acid synthesis, protein synthesis, or cell wall synthesis; intracellular activity without major membrane disruption. | [28] |
| Antibacterial peptides | Defensins, cathelicidins, nisin | Humans, amphibians, bacteria | Broad-spectrum antibacterial activity; kills Gram-positive and Gram-negative bacteria. | [29] |
| Antifungal peptides | Histatins, dermaseptins | Humans (saliva), frogs | Disrupt fungal membranes; inhibit fungal enzymes and adhesion. | [30] |
| Antiviral peptides | LL-37, defensins, melittin | Humans, insects | Block viral entry, fusion, or replication; potential against human immunodeficiency virus (HIV), influenza, and coronaviruses. | [31] |
| Antiparasitic peptides | Dermaseptins, cecropins | Frogs, insects | Active against protozoan parasites (e.g., Leishmania, Plasmodium). | [32, 33] |
| ACPs | Magainin II, lactoferricin, melittin | Frogs, humans, bees | Selectively disrupt cancer cell membranes due to higher negative charge; induce apoptosis. | [34] |
ACPs: anticancer peptides.
The author thanks Graphic Era (Deemed to be University), Dehradun, India. We would like to thank Paperpal (https://paperpal.com/), Cactus Communications Services Pte Ltd., Singapore, for their invaluable online assistance in refining the language and grammar of our manuscript.
RK: Conceptualization, Investigation, Writing—original draft, Writing—review & editing. The author read and approved the submitted version.
The author declares that there are no conflicts of interest.
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