The NMR structure of human β-defensin-2 reveals a novel α-helical segment

Human beta -defensin-2 (HBD-2) is a member of the defensin family of antimicrobial peptides. HBD-2 was first isolated from inflamed skin where it is posited to participate in the killing of invasive bacteria and in the recruitment of cells of the adaptive immune response. Static light scattering and two-dimensional proton nuclear magnetic resonance spectroscopy have been used to assess the physical state and structure of HBD-2 in solution. At concentrations of less than or equal to2.4 mM, HBD-2 is monomeric. The structure is amphiphilic with a nonuniform surface distribution of positive charge and contains several key structural elements, including a triple-stranded, antiparallel beta -sheet with strands 2 and 3 in a beta -hairpin conformation. A beta -bulge in the second strand occurs at Gly28, a position conserved in the entire defensin family. In solution, HBD-2 exhibits an alpha -helical segment near the N-terminus that has not been previously ascribed to solution structures of alpha -defensins or to the beta -defensin BNBD-12. This novel structural element may be a factor contributing to the specific microbicidal or chemokine-like properties of HBD-2.