5 research outputs found
Folded Structure and Insertion Depth of the Frog-Skin Antimicrobial Peptide Esculentin-1b(1–18) in the Presence of Differently Charged Membrane-Mimicking Micelles
Antimicrobial peptides (AMPs) are
effectors of the innate immunity
of most organisms. Their role in the defense against pathogen attack
and their high selectivity for bacterial cells make them attractive
for the development of a new class of antimicrobial drugs. The N-terminal
fragment of the frog-skin peptide esculentin-1b (Esc(1–18))
has shown broad-spectrum antimicrobial activity. Similarly to most
cationic AMPs, it is supposed to act by binding to and damaging the
negatively charged plasma membrane of bacteria. Differently from many
other AMPs, Esc(1–18) activity is preserved in biological fluids
such as serum. In this work, a structural investigation was performed
through NMR spectroscopy. The 3D structure was obtained in the presence
of either zwitterionic or negatively charged micelles as membrane
models for eukaryotic and prokaryotic membranes, respectively. Esc(1–18)
showed a higher affinity for and deeper insertion into the latter
and adopted an amphipathic helical structure characterized by a kink
at the residue G8. These findings were confirmed by measuring penetration
into lipid monolayers. The presence of negatively charged lipids in
the bilayer appears to be necessary for Esc(1–18) to bind,
to fold in the right three-dimensional structure, and, ultimately,
to exert its biological role as an AMP
Circular Dichroism analysis.
<p><b>(A)</b> Conventional CD spectra of both SB056-lin and β-SB056-lin in the presence of POPC/POPG (1/1 mol/mol) SUVs. <b>(B)</b> SRCD spectra of both SB056-lin and β-SB056-lin in the presence of POPC/POPG (1/1 mol/mol) SUVs. SRCD spectra of <b>(C)</b> SB056-lin and <b>(D)</b> β-SB056-lin in the presence of differently charged SUVs.</p
MIC values of SB056-lin and β-SB056-lin against two Gram-negative and two Gram-positive bacterial strains.
<p>MIC values of SB056-lin and β-SB056-lin against two Gram-negative and two Gram-positive bacterial strains.</p
Schematic representation of the peptides.
<p><b>(A)</b> Original SB056-lin, and <b>(B)</b> sequence-optimized β-SB056-lin. Yellow circles indicate hydrophobic residues, blue ones positively charged amino acids, and cyan indicates the polar serine residue.</p
Summary of peptide-lipid interactions.
<p>The proportion of anionic lipids in the vesicles is increased from top to bottom. The behavior of the original SB056-lin peptide is represented on the left hand side, and the sequence-optimized β-SB056-lin on the right. Black arrows of different length and thickness are used to indicate the different binding equilibria. SB056-lin binds only to anionic bilayers, and in a not so well-ordered β-stranded conformation. The sequence optimized β-SB056-lin, on the other hand, forms regular β-strands that self-assemble into extended β-sheets when the negative charge of the bilayer exceeds electro-neutrality of the peptide-lipid system.</p