NMR Structure and Localization of the Host Defense Peptide ThanatinM21F in Zwitterionic Dodecylphosphocholine Micelle: Implications in Antimicrobial and Hemolytic Activity.

Non-hemolytic antimicrobial peptides (AMPs) are vital lead molecules for the designing and development of peptide-based antibiotics. Thanatin a 21-amino acid long single disulfide bonded AMP is known to be highly non-hemolytic with a limited toxicity to human cells and model animals. Thanatin demonstrates a potent antibacterial activity against multidrug-resistant Gram-negative pathogens. A single mutated variant of thanatin replaced last residue Met21 to Phe or thanatin M21F has recently been found to be more active compared to the native peptide. In order to gain mechanistic insights toward bacterial cell lysis versus non-hemolysis, here, we report atomic resolution structure and mode insertion of thanatinM21F reconstituted into zwitterionic detergent micelle by use of solution NMR spectroscopy. The 3D structure of thanatinM21F in DPC micelle is defined by an anti-parallel β-sheet between residues I9-F21 with a central cationic loop, residues N12-R14. PRE NMR studies revealed hydrophobic core residues of thanatinM21F are deeply inserted in the DPC micelle, while residues at the extended N-terminal half of the peptide are appeared to be mostly surface localized. Marked structural differences of thanatin and thanatinM21F in negatively charged LPS and DPC micelle could be correlated with non-hemolytic and antibacterial activity.