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. 2022 Mar 6;11(3):349. doi: 10.3390/antibiotics11030349

Figure 2.

Figure 2

Bacterial membrane structures and mechanisms of action of antimicrobial peptides (AMPs). (a) Schematic membrane structures of Gram-positive and Gram-negative bacteria. The cytoplasmic membranes of them are similar. Gram-negative bacteria have a thin layer of peptidoglycan, with lipopolysaccharide (LPS) in the outer membrane. In contrast, Gram-positive bacteria have a thick layer of peptidoglycan surrounding the cytoplasmic membrane, with lipoteichoic acid (LTA) across the peptidoglycan layer. Both LPS and LTA are the binding targets of AMPs. (b) Mechanisms of action of AMPs. Membrane-active AMPs interrupt the integrity of the membrane by forming different pores as in the following models: (1) Barrel-Stave model: AMPs perpendicularly insert into the lipid bilayer of the membrane and form a channel. (2) Carpet model: AMPs cover the surface of the membrane without forming specific pores. (3) Toroidal pore model: AMPs also insert perpendicularly in the lipid bilayer without specific peptide–peptide interactions to form a channel. (4) Detergent-like mode: AMPs work like a detergent to break membranes into small pieces.