Effect of Antimicrobial Peptides from Australian Tree Frogs on Anionic Phospholipid Membranes

Abstract

Skin secretions of numerous Australian tree frogs contain antimicrobial peptides that form part of the host defense mechanism against bacterial infection. The mode of action of these antibiotics is thought to be lysis of infectious organisms via cell membrane disruption, on the basis of vesicle-encapsulated dye leakage data [Ambroggio et al. (2005) Biophys. J. 89, 1874-1881]. A detailed understanding of the interaction of these peptides with bacterial membranes at a molecular level, however, is critical to their development as novel antibacterial therapeutics. We focus on four of these peptides, aurein 1.2, citropin 1.1, maculatin 1.1, and caerin 1.1, which exist as random coil in aqueous solution but have alpha-helical secondary structure in membrane mimetic environments. In our earlier solid-state NMR studies, only neutral bilayers of the zwitterionic phospholipid dimyristoylphosphatidylcholine (DMPC) were used. Deuterated DMPC ( d 54-DMPC) was used to probe the effect of the peptides on the order of the lipid acyl chains and dynamics of the phospholipid headgroups by deuterium and (31)P NMR, respectively. In this report we demonstrate several important differences when anionic phospholipid is included in model membranes. Peptide-membrane interactions were characterized using surface plasmon resonance (SPR) spectroscopy and solid-state nuclear magnetic resonance (NMR) spectroscopy. Changes in phospholipid motions and membrane binding information provided additional insight into the action of these antimicrobial peptides. While this set of peptides has significant C- and N-terminal sequence homology, they vary in their mode of membrane interaction. The longer peptides caerin and maculatin exhibited properties that were consistent with transmembrane insertion while citropin and aurein demonstrated membrane disruptive mechanisms. Moreover, aurein was unique with greater perturbation of neutral versus anionic membranes. The results are consistent with a surface interaction for aurein 1.2 and pore formation rather than membrane lysis by the longer peptides.

Solid‐state NMR spectroscopic studies on the interaction of sorbic acid with phospholipid membranes at different pH levels

“…The changes in the 31 P isotropic T 1 values provide measurements of the amplitude of motion fluctuations on the fast (10 −9 s) time scale, indicating changes in individual lipid dynamics. [35] Our 31 P T 1 values of pure DMPC MLV samples at 35 °C are in close agreement with a previously reported T 1 value of 660 ms at the phosphorous frequency of 60.7 MHz and at 30 °C. [36] As shown in Fig.…”

Lysyl-Phosphatidylglycerol Attenuates Membrane Perturbation Rather than Surface Association of the Cationic Antimicrobial Peptide 6W-RP-1 in a Model Membrane System: Implications for Daptomycin Resistance

“…It is not clear why this process per se should lead to an inhibition of dye leakage from vesicles; it is conceivable that the presence of the positively charged lysyl-PG leads to an overall stabilization of a membrane rich in anionic PG. The possibility of PG domain formation in mixed lipid vesicles induced by the binding of a cationic peptide has been suggested previously (2)(3)(4).…”

Bacteria May Cope Differently from Similar Membrane Damage Caused by the Australian Tree Frog Antimicrobial Peptide Maculatin 1.1

“…These results are in agreement with previous reports suggesting that Mac1 is selective toward Gram-positive bacteria. Such preference was suggested to correlate with higher amount of negatively charged lipids in Gram-positive when compared with Gram-negative bacteria (24). Mac1 is less efficient in inhibiting the growth of bacteria than the bee venom peptide melittin, also known for its antimicrobial activity (25), with the latter inhibiting bacterial growth at 2 and 0.5 M against E. coli and S. aureus, respectively (Table 1).…”