AMPs are polypeptides comprising about 50 amino acids or less, which usually means in the range of 5 to 30 amino acid residues. Bigger proteins may incorporate structures that include certain peptide epitopes that exert potent antimicrobial effects. Each AMP has a broad spectrum of antimicrobial activity that is unique to the polypeptide. Thus numerous AMPs can disrupt and lyse Gram-negative and Gram-positive bacteria, fungi as well as certain viruses.
Due to the potential lytic properties of AMPs against bacterial as well as mammalian membranes, one of the challenges in designing new peptides relies on developing AMPs with high specificity against bacterial or fungal cells without casing toxic effects to human cells, i.e., a high therapeutic index (minimum hemolytic concentration/minimum effective concentration; MHC/MEC). See the schematic diagram below.
A schematic diagram demonstrating the essential difference between mammalian and bacterial cell membranes with respect to an interaction of an AMP (the black corkscrew-like shape on the top of the figure). Since most AMPs are cationic (the blue cluster with + symbols), a strong interaction occurs. Thus AMPs selectively target the bacterial membrane.