How Many AMP Molecules Kill a Bacterium? Spectroscopic Determination of PMAP-23 Binding to E. Coli

Abstract

Pore forming toxins (PFTs) are ubiquitous weapons in the armoury of many organisms. It is often observed that small numbers of these potent proteins form stable pores, permeabilize the cell membrane and cause cell lysis. The complex role of the membrane in the formation of these pores, the influence of the pore on the structure and dynamics of the surrounding membrane and the expulsion of the central lipids upon pre-pore formation are important phenomena that are poorly understood due to the paucity of structural data. Multi-scale molecular dynamics was carried out on the PFT Cytolysin-A (ClyA), to address its interaction with the surrounding lipid membrane. A large heterogeneity in the lipid self-diffusivities were observed with the presence of more mobile and less mobile lipid fractions spanning the membrane. These results indicate that the local environment around the protein complex is markedly different from the rest of the membrane. Simulations of intermediate ClyA oligomers in a variety of membranes shows rapid evacuation of the central lipids from the interior to the free membrane surrounding the partially formed pore assembly. This implies that concerted lipid expulsion occurs prior to the formation of the dodecameric pore complex. This alternative hypothesis challenges the notion that destabilization and ejection of a membrane patch corresponding to the pore-lumen occurs after the pre-pore assembly on the membrane surface is complete. This mechanism could occur across PFT families and has implications on membrane resealing and cell recovery.

Investigations of the synergistic enhancement of antimicrobial activity in mixtures of magainin 2 and PGLa

“…Notably, such biophysical data correlate well with their activities observed in antibacterial assays [27],…”

The SMART model: Soft Membranes Adapt and Respond, also Transiently, in the presence of antimicrobial peptides

“…Although at the present time the question how synergism occurs cannot be answered, it is interesting to note that the situation resembles that of the early 1990s where the structural data indicated that cationic amphipathic peptides reside at the membrane interface rather than adopt a TM alignment . Years of research were needed to accumulate sufficient experimental data to conclusively show that membrane openings and antimicrobial activities can be explained with such in‐plane alignments . In a related manner, our initial view of synergism to occur by the formation of TM helical bundles made by the ensemble of interacting peptides is in disagreement with biophysical data , and novel ideas need to be developed.…”

“…A number of observations point to a direct interaction of these peptides with phospholipid membranes of bacteria and fungi where they often disrupt the bilayer integrity. These AMPs inhibit the growth of sensitive microorganisms, exhibit cell killing activities and/or enter into the cell interior . In addition, they have been found to modulate the immune response of the host organisms.…”

“…Finally, it should be considered that many peripheral membrane proteins and components associate through electrostatic interactions. With a high density of cationic AMPs , screening the negative charges causes the release of many of these proteins, thereby interfering with cell viability .…”

The Mechanisms of Action of Cationic Antimicrobial Peptides Refined by Novel Concepts from Biophysical Investigations

“…These cationic linear peptides are random coil in solution and adopt their three-dimensional amphipathic helical structure only when interacting with membranes. By disrupting the integrity of bacterial and fungal membranes, they inhibit the growth of microorganisms and/or enter into the cell interior (Roversi et al 2014). This results in complex patterns of metabolic reactions by the bacterial cells (Kozlowska et al 2014;Cardoso et al 2017).…”