title: Deciphering a mechanism of membrane permeabilization by α-hordothionin peptide.
abstract: α-Hordothionin (αHTH) belongs to thionins, the plant antimicrobial peptides with membrane-permeabilizing activity which is associated with broad-range antimicrobial activity. Experimental data have revealed a phospholipid-binding site and indicated formation of ion channels as well as membrane disruption activity of thionin. However, the mechanism of membrane permeabilization by thionin remained unknown. Here it is shown that thionin is a small water-selective channel. Unbiased high-precision molecular modeling revealed formation of a water-selective pore running through the αHTH double α-helix core when the peptide interacted with anions. Anion-induced unfolding of the C-end of the α2-helix opened a pore mouth. The pore started at the α2 C-end between the hydrophilic and the hydrophobic regions of the peptide surface and ended in the middle of the unique hydrophobic region at the C-end of the α1-helix. Highly conserved residues including cysteines and tyrosine lined the pore walls. A large positive electrostatic potential accumulated inside the pore. The narrow pore was, nonetheless, sufficient to accommodate at least one water molecule along the channel except for two constriction sites. Both constriction sites were formed by residues participating in the phospholipid-binding site. The channel properties resembled that of aquaporins with two selectivity filters, one at the entrance, inside the α2 C-end cavity, and a second in the middle of the channel. It is proposed that the αHTH water channel delivers water molecules to the bilayer center that leads to local membrane disruption. The proposed mechanism of membrane permeabilization by thionins explains seemingly controversial experimental data.
authors.affiliation: School of Plant, Environmental, and Soil Sciences, Louisiana State Agricultural Center, Louisiana State University, Baton Rouge, LA 70803, USA. soard@agctr.lsu.edu
authors.forename: Svetlana V
authors.initials: SV
authors.lastname: Oard
mesh_terms: D000595:Amino Acid Sequence; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010455:Peptides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D010718:Phosphatidylserines / Q000737:chemistry / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D014867:Water / Q000737:chemistry / Q000378:metabolism
chemical_list: D023181:Antimicrobial Cationic Peptides; D008051:Lipid Bilayers; D010455:Peptides; D010718:Phosphatidylserines; D010940:Plant Proteins; C036092:hordothionin protein, Hordeum vulgare; D014867:Water; C050294:1-palmitoyl-2-oleoylglycero-3-phosphoserine