Antimicrobial Peptide Lab Report

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Antimicrobial peptides (AMPs) are a class of host defence peptides found in all living organisms. They exhibit significant activity against bacteria, virus, fungi and several other pathogens. AMPs share certain common features. (a) They are small molecules with varying amino acid composition and length. (b) They are cationic, due to the presence of positively charged basic amino acids and (c) amphipathic, since they contain alternate hydrophobic nonpolar and hydrophilic, polar residues. AMPs are grouped into 4 major categories based on structure. These are β-sheet, α-helical, loop, and extended peptides, with the linear, α-helical, amphipathic type being the most abundant. [3]
AMPs usually exhibit their antimicrobial effect using a mechanism that involves disruption, followed by an increase in the permeability of the outer membrane (OM) of the bacterial cell which allows the efflux of essential ions and nutrients. Although the exact process is not very clear, several mechanisms have been proposed to explain the behaviour of AMPs, mainly (1) carpet-like mechanism (2) barrel-stave mechanism and (3) toroidal mechanism. [1]
In the carpet-like mechanism, the AMPs initially bind to the surface of the target cell membrane and cover it partially or
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Most antimicrobial peptides contain well-defined cationic domains and display a net positive charge ranging from +2 to +9. Cationicity is important as it influences the degree of electrostatic attraction of antimicrobial peptides towards negatively charged phospholipid membranes of bacteria and other microorganisms. Consequently, the polycationic AMPs are selectively attracted to the negatively charged bacterial targets but not to the mammalian cells, which is the very first step in their mechanism of action. This mutual electron affinity is responsible for selective antimicrobial targeting relative to host tissues.

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