Table 1.

Classification of AMPs into four clusters based on their structure

Sample No.	Type of AMP	Structure	Property	Example	Basic structure	Reference
1	Type I: linear α-helical peptides	Highly positively charged Unstructured in aqueous solution, and fold into their α-helical configuration when they bind to the bacterial membrane	27% of peptides belong to this group Cationic amphipathic helices Capping at the N- and C-terminus stabilizes the helix Kill the microbes by creating channels in the membranes	Alamethicin, cecropin, magainin, LL-37	$$	22
2	Type II:cyclic peptides with β-sheet structure	1–5 disulfide bonds Stably assembled by either disulfide bonds or cyclization of the peptide backbone	Number of disulfide bonds decide degree of cyclic conformation Exist in β-sheet conformation in aqueous solution Act on intracellular targets Enter cell by lipid flip-flop movement	Tachyplesins, defensins, protegrins, polymyxin	$$	23
3	Type III: extended peptide	Linear in shape No secondary structure	Over representation of 1 type of amino acid Rich in proline and/or glycine, tryptophan or histidine Aggregate in the membranes and create a voltage-induced channel, the peptides are translocated into cytoplasm	Histatin histidine),ritrpticin (arginine), diptericins(glycine),indolicidin	$$	24
4	Type IV:looped peptide	Looped structure due to the single disulfide, amide or isopeptide bond Antiparallel β-sheet orientation	Short in size, easy to synthesize and proteolytically stable	Lantibiotics	$$	23