The Role of Greasy Residues in Teixobactin Derivatives

Abstract

Teixobactin is a novel antibiotic that inhibits cell wall biosynthesis by binding to cell wall precursors, such as lipid II. Previously, we characterized multiple conformations of the teixobactin-lipid II complex in membrane using modeling and molecular dynamics simulations (Chem. Sci., 2018, 9:6997-7008). Common structural features shared by these conformations include pyrophosphate coordination by the C-terminal cyclodepsipeptide ring and membrane anchoring by the mid-chain hydrophobic residues. Since the cell wall precursors exist in low concentrations at bacterial surfaces, it is likely that teixobactin binds and inserts into the membrane before reaching its targets. Here, we performed microsecond-scale molecular dynamics simulations to investigate the membrane binding and insertion of teixobactin and a highly potent derivative (D-Arg4/Ile10-teixobactin) in the absence of their target molecules. Multiple membrane models were employed in our simulations, including the Highly Mobile Membrane Mimetic model and full-length phospholipid bilayers, consisting of either zwitterionic phosphatidylethanolamines or anionic phosphatidylglycerols. We found that teixobactin derivatives always anchor to the membrane using residues N-Me-D-Phe1, Ile2, D-allo-Ile5, Ile6, and Ile11. In particular, the insertion depths of the N-terminal hydrophobic residues are consistently comparable to those of the mid-chain hydrophobic anchors, implying they also play a significant role in membrane insertion. Additionally, the membrane insertion of Ile11 restricts the orientation of the cyclodepsipeptide ring at the membrane surface, suggesting that one of the lipid II-bound forms characterized in our earlier work would be more prominent due to a compatible cyclodepsipeptide ring orientation. In summary, almost half of the side chains in teixobactin participate in membrane-anchoring and not direct lipid II-binding. These hydrophobic residues appear invariable in several studies of the structure-activity relationship of teixobactin derivatives, suggesting that membrane binding and insertion act as an essential step in its antibacterial mechanism.