Arginine in α-Defensins DIFFERENTIAL EFFECTS ON BACTERICIDAL ACTIVITY CORRESPOND TO GEOMETRY OF MEMBRANE CURVATURE GENERATION AND PEPTIDE-LIPID PHASE BEHAVIOR

The conserved tridisulfide array of the alpha-defensin family imposes a common triple-stranded beta-sheet topology on peptides that may have highly diverse primary structures, resulting in differential outcomes after targeted mutagenesis. In mouse cryptdin-4 (Crp4) and rhesus myeloid alpha-defensin-4 (RMAD4), complete substitutions of Arg with Lys affect bactericidal peptide activity very differently. Lys-for-Arg mutagenesis attenuates Crp4, but RMAD4 activity remains mostly unchanged. Here, we show that the differential biological effect of Lys-for-Arg replacements can be understood by the distinct phase behavior of the experimental peptide-lipid system. In Crp4, small-angle x-ray scattering analyses showed that Arg-to-Lys replacements shifted the induced nanoporous phases to a different range of lipid compositions compared with the Arg-rich native peptide, consistent with the attenuation of bactericidal activity by Lys-for-Arg mutations. In contrast, such phases generated by RMAD4 were largely unchanged. The concordance between small-angle x-ray scattering measurements and biological activity provides evidence that specific types of alpha-defensin-induced membrane curvature-generating tendencies correspond directly to bactericidal activity via membrane destabilization.