Supramolecular Interactions of Teixobactin Analogues in the Crystal State

Teixobactin is a potent peptide antibiotic against Gram-positive bacteria that binds to lipid II and related peptidoglycan precursors and disrupts the cell membrane. This paper presents the X-ray crystallographic structure of the N-methylated teixobactin analogue N-Me-D-Gln4,Lys10-teixobactin (1). N-Methylation at position 4 prevents uncontrolled aggregation and enables the crystallization of the teixobactin analogue. Lysine at position 10 replaces the non-proteinogenic amino acid allo-enduracididine, which is not commercially available. Crystallization from aqueous solution with MgCl2 and PEG3350 afforded crystals suitable for X-ray crystallography. The crystallographic phases were solved using SAD phasing on data sets collected at 2.0663 [A]. Molecular replacement then enabled the determination of the structure at 1.50 [A] resolution using a data set collected at 0.9997[A] (PDB 8U78). Eight peptide molecules comprise the asymmetric unit, with each peptide molecule binding a chloride anion through hydrogen bonding with the amide NH group of residues 7, 8, 10, and 11. The peptide molecules form hydrogen-bonded antiparallel {beta}-sheet dimers in the crystal lattice, with residues 1-3 comprising the dimerization interface. The dimers further assemble end-to-end in the crystal lattice. The {beta}-sheet dimers are amphiphilic, with the side chains of the hydrophobic residues on one surface and the side chains of the hydrophilic residues on the other surface. The dimers pack in the lattice through hydrophobic interactions between the hydrophobic surfaces. The crystal structure of teixobactin analogue 1 recapitulates several aspects of the interaction of teixobactin with the cell membrane of Grampositive bacteria, including anion binding, supramolecular assembly through {beta}-sheet formation, and hydrophobic interactions.