Antimicrobial Peptide (AMP): Definition

Detailed Explanation

Antimicrobial peptides are ancient weapons of the innate immune system, found in virtually every organism from insects to humans. Most are short (12–50 amino acids), positively charged (net charge +2 to +9), and amphipathic — properties that allow them to selectively target negatively charged bacterial membranes while sparing the neutral membranes of host cells.

AMPs kill microbes primarily by disrupting their cell membranes through several proposed mechanisms: the barrel-stave model (peptides insert like staves of a barrel to form transmembrane pores), the toroidal pore model (peptides and lipids together form a hole), and the carpet model (peptides accumulate on the surface until the membrane disintegrates). Some AMPs also have intracellular targets, inhibiting DNA, RNA, or protein synthesis after entering the cell.

Humans produce several AMP families. Cathelicidins (LL-37) are found in neutrophils and epithelial cells. α-Defensins are concentrated in neutrophil granules and intestinal Paneth cells. β-Defensins are expressed in skin, airways, and the urogenital tract. Because AMPs use physical membrane disruption rather than specific metabolic targets, bacteria develop resistance to them far more slowly than to conventional antibiotics — making AMPs promising candidates for next-generation anti-infective drugs.

Key Facts