Preparation of isotopically labelled recombinant β-defensin for NMR studies

β-Defensins are a family of cationic peptides that contain six invariant cysteine residues that form characteristic disulfide bonds between Cys1–Cys5, Cys2–Cys4 and Cys3–Cys6. They have been shown to act as potent antimicrobial agents and chemokines. Human β-defensin 2 (HBD2) was first isolated from psoriatic skin lesions and the structure of this peptide has been solved by X-ray crystallography and NMR spectroscopy both of which are consistent with a fold that contains an N-terminal α-helix and three antiparallel β-strands. Here, we report the expression and purification of the first isotopically labelled β-defensin (15N HBD2) with 100% incorporation of 15N using a recombinant Escherichia coli method. Multidimensional NMR spectroscopy experiments: 2D 1H–15N HSQC, 3D HSQC-TOCSY and 3D HSQC-NOESY allows for the assignment of resonances with no overlapping or ambiguous peaks. This isotopically labelled peptide is highly suitable for studying the interactions between HBD2 and a range of components from both the mammalian immune system and bacterial pathogens.