The Lipid Dependence of Antimicrobial Peptide Activity Is an Unreliable Experimental Test for Different Pore Models

Abstract

The role played by glutathione transferase P1-1 (GSTP1-1) in modulating the c-Jun N-terminal kinase (JNK) pathway has been extensively investigated using JNK isoforms known to exert opposite effects in the cells. We have expressed isoform JNK1α2, which has been reported to transmit a pro-apoptotic signal, and we have analyzed both the phosphorylation level and the activity of this kinase in the presence of GSTP1-1. Contrary to what previous studies suggest, we found that GSTP1-1 is able to form a complex with the unphosphorylated and inactive JNK1α2 isoform, even in the absence of the substrate. We also analyzed the consequences of this interaction on the activity of both enzymes. The complex strongly reduced the extent of activation of JNK1α2 and preserved GSTP1-1 from inactivation. Unexpectedly, glutathione (GSH) exerted a negative effect on the affinity of GSTP1-1 for JNK1α2, suggesting that the intracellular levels of this thiol may allow a fine-tuning of the MAPK signaling pathway. Moreover, we found that the adduct formed by GSH and the strong GSTP1-1 inhibitor NBDHEX abolishes the interaction between GSTP1-1 and JNK1α2. These data confirm and extend at the molecular level previous evidence obtained in tumor cell lines.

From liposomes to cells: Filling the gap between physicochemical and microbiological studies of the activity and selectivity of host‐defense peptides

“…For instance, it is possible to determine peptide conformation, aggregation state, depth of insertion, orientation in the membrane and distribution between the two leaflets of the bilayer. Studies from our group have demonstrated that many of these phenomena modulate the final peptide membrane‐perturbing activity: peptide aggregation in water can compete with membrane binding and modulate peptide activity and selectivity; conformational equilibria can modulate the effective peptide hydrophobicity and therefore its tendency to associate to different membranes; peptide orientation and aggregation in the bilayer determine the structure of the pores …”

Antimicrobial peptides from scorpion venoms

“…This has led to the proposal of a new interfacial model for AMP action (Wimley, 2010;Marks et al, 2011), which is a hybrid between the classical carpet model and the more recent toroidal model. The interfacial model consists of three main processes that take place consecutively: (i) an initial electrostatic interaction with the negatively charged bacterial membrane driven by the polar face; (ii) an interaction with the membrane hydrophobic core driven by the peptide hydrophobic face, causing the peptide to insert into the membrane, and (iii) the polar pocket interacts with the phospholipid head groups on the inner membrane leaflet causing negative curvature of this inner membrane (Marks et al, 2011;Bobone et al, 2012).…”

“…Whether one is a philosophical hunter or gatherer, it cannot be contested that a more detailed biophysical approach to understanding the mechanisms of action of these new peptides is essential if they are to have a positive impact on the clinical management of infection. Techniques such as NMR (Nomura et al, 2004(Nomura et al, , 2005, atomic force microscopy (AFM) (Garcia-Sa ez, 2007;Fernandez et al, 2012;Lam et al, 2012), secondary ionisation mass spectrometry (SIMS) (Rakowska et al, 2013) and X-ray photoemission electron microscopy (Won et al, 2011) can enable us to re-examine and refine our present interpretations of models of peptide interaction with microbial membranes (Bobone et al, 2012;Marks et al, 2011). Such experimental methods, taken together with molecular techniques to determine potential intracellular targets (e.g.…”

Immunomodulatory effects of anti-microbial peptides

“…Apparently, the fine details of the membrane-peptide interaction are dependent upon the specifics of both players of the association, as while magainin, a frog skin AMP, lies in the plane of the bi-layer; M2 delta, a helical segment of the nicotinic acetylcholine receptor, spans the membrane, perpendicular to the bi-layer plane [13]. It slowly became clear that the biophysical assumptions of neither of the two main membrane-perturbing models (barrel-stave and Shai-Matsuzaki-Huang carpet) are reliable for reaching structure-function conclusions [14]. The last push for alternative modes of action came after the observations that many AMPs fail to modulate membrane permeability at their microbiologically active concentration [15].…”