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

Human β-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 ≤ 2.4 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 β-sheet with strands 2 and 3 in a β-hairpin conformation. A β-bulge in the second strand occurs at Gly28, a position conserved in the entire defensin family. In solution, HBD-2 exhibits an α-helical segment near the N-terminus that has not been previously ascribed to solution structures of α-defensins or to the β-defensin BNBD-12. This novel structural element may be a factor contributing to the specific microbicidal or chemokine-like properties of HBD-2.