Solution Structure and Model Membrane Interactions of P-113, a Clinically Active Antimicrobial Peptide Derived from Human Saliva

P-113, AKRHHGYKRKFH-NH2, was derived from human saliva and found to possess clinical activity against fungus infections in HIV patients with oral candidiasis. We have determined the solution structure of P-113 bound to membrane-mimetic SDS micelles by two-dimensional NMR methods. The SDS micelle-bound structure of P-113 adopts an alpha-helical segment and the positively charged residues are clustered together to form a hydrophilic patch. A variety of biophysical and biochemical experiments, including circular dichroism, fluorescence spectroscopy and microcalorimetry, were used to show that P-113 interacted with negatively charged phospholipid vesicles and induced dye release from these vesicles. However, its dye leakage efficiency is much less than the results of previously reported antimicrobial peptides. These results suggest that the antimicrobial activity of P-113, unlike other antimicrobial peptides, may act not only through binding to and destabilization of the microbial membrane but also through a specific protein receptor on the microbial cell surface.