Transmembrane Pore Structures of β-Hairpin Antimicrobial Peptides by All-Atom Simulations

Protegrin-1 is an 18-residue β-hairpin antimicrobial peptide (AMP) that has been suggested to form transmembrane β-barrels in biological membranes. However, alternative structures have also been proposed. Here, we performed multimicrosecond, all-atom molecular dynamics simulations of various protegrin-1 oligomers on the membrane surface and in transmembrane topologies. The membrane surface simulations indicated that protegrin dimers are stable, whereas trimers and tetramers break down. Tetrameric arcs remained stably inserted in lipid membranes, but the pore water was displaced by lipid molecules. Unsheared protegrin β-barrels opened into β-sheets that surrounded stable aqueous pores, whereas tilted barrels with sheared hydrogen bonding patterns were stable in most topologies. A third type of observed pore consisted of multiple small oligomers surrounding a small, partially lipidic pore. We also considered the β-hairpin AMP tachyplesin, which showed less tendency to oligomerize than protegrin: the octameric bundle resulted in small pores surrounded by six peptides as monomers and dimers, with some peptides returning to the membrane surface. The results imply that multiple configurations of protegrin oligomers may produce aqueous pores and illustrate the relationship between topology and putative steps in protegrin-1's pore formation. However, the long-term stability of these structures needs to be assessed further.