Structural changes induced in thionins by chloride anions as determined by molecular dynamics simulations

Computational analysis of two membrane-permeabilizing peptides, barley alpha-hordothionin and wheat beta-purothionin, revealed that anions can trigger dynamic and structural changes in the thionin antiparallel double alpha-helix core. Analysis of the molecular dynamics simulations demonstrated that anions induced unfolding of the alpha 2 and alpha 1 helices at the carboxyl ends which are located on the opposite ends of the alpha-helix Core. An internalized water molecule was observed inside the unfolded alpha 2 C-end. Strong interactions of anions with the R30 regulating network of simultaneous interactions of anions with the phospholipid-binding site and the R30 hydrogen bonding network triggered unfolding of the alpha 2 C-end. An increase of anion density for two residues of the phospholipid-binding site (K1, R17, and Q22) or R17 and R19 and a preceding unfolding of the alpha 2 C-end were necessary for unfolding of the alpha 1 C-end. Anions interacted primarily with residues of the phospholipid-binding site and the R30 network while the alpha 1/alpha 2 hydrophobic region was void of anions. However, during strong interactions of anions with the R30 network and phospholipid-binding site, the alpha 1/alpha 2 hydrophobic region attracted anions which interacted with conserved residues of the alpha 1 C-end. Analysis of anion-induced rearrangements pointed to auxiliary residues of the R30 network and the phospholipid-binding site. Induction of conformational changes on the opposite ends of the alpha-helix core by interactions of anions with the phospholipid-binding site may be relevant to a mechanism of membrane-permeabilizing activity. Published by Elsevier B.V.