Abstract
L-phenylseptin (L-Phes) and D-phenylseptin (D-Phes) are amphibian antimicrobial peptides isolated from the skin secretion of Hypsiboas punctatus. In the N-termini, L-Phes and D-Phes contain three consecutive phenylalanine residues, l-Phe-l-Phe-l-Phe and l-Phe-d-Phe-l-Phe, respectively. They are known to exhibit antimicrobial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Xanthomonas axonopodis pv. Glycines. However, their mechanism of action and the role of the D-amino acid residue have not been elucidated yet. In this study, the interactions of both peptides with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were investigated by means of quartz crystal microbalance, circular dichroism, vibrational circular dichroism, 31P solid-state NMR, and molecular dynamics simulation. Both peptides have similar binding constants to the DMPC lipid bilayers, in the order of 106 M−1, and form an α-helix structure in the DMPC lipid bilayers. Both the peptides induce similar changes in the dynamics of DMPC lipids. Thus, in spite of the difference in the conformations caused by the chirality at the N-terminus, the peptides showed similar behavior in the membrane-bound state, experimentally and computationally.
Highlights
Antimicrobial peptides are promising candidates for new antibiotics and have broad-spectrum activity against gram-negative and gram-positive bacteria, fungi, and parasites [1,2]
quartz crystal microbalance (QCM) can estimate the affinity of membrane-bound peptide with immobilized membrane [41,42]
The binding constant values showed that D-Phes has a slightly stronger affinity to DMPC membrane. These results indicated that the differences in the N-terminal structure might be manifest as differences in the affinity and antimicrobial activity
Summary
Antimicrobial peptides are promising candidates for new antibiotics and have broad-spectrum activity against gram-negative and gram-positive bacteria, fungi, and parasites [1,2]. These peptides are amphipathic in nature and tend to adopt α-helices in the membrane. The membrane interactions play a major role in the peptide functions. Even before their antimicrobial activity, the peptides may get degraded by the target organisms [5]. Incorporation of one or more d-amino acids into these peptides has received significant attention in recent decades [6]
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