Inclusion of Menaquinone in Lipid Membranes Decreases Susceptibility to Antimicrobial Peptides

Abstract

We have utilized our recently developed method to characterize lipid areas of various phospholipids with varying numbers of carbons and double bonds. In the case of lipids with unsaturated fatty acid chains our results suggest that lipid areas change with increasing hydrocarbon chain length, but not linearly-lateral lipid area is the result of the fine balance between the hydrocarbon chain length and double bond position. Furthermore, we discovered that the most dramatic change in lipid area occurs after the introduction of the first double bond to the lipid's acyl chains. Besides their importance in biology, lipid areas play a central role in molecular dynamics (MD) simulations, where their inconsistencies have been highlighted by the disparate results arising from MD simulations using different force fields. Since MD force fields are considered to be "well tuned" if they are able to reproduce experimental data, more reliable experimental information is necessary for their future development. 3388-Pos Board B493 Cardiolipin, a Key Component to Mimic the E. coli Bacterial Membrane in Model System Membranes Sílvia Lopes, Cristina Neves, Peter Eaton, Paula Gameiro. The phase transition temperatures of several lipidic systems were determined using two different techniques: dynamic light scattering (DLS) and steadystate fluorescence anisotropy, using two fluorescent probes that report different membrane regions (TMA DPH and DPH). Atomic force microscopy (AFM) was used as a complementary technique to characterize different lipid model systems under study. The systems were chosen due to the increased interest in bacterial membrane studies due to the problem of antibiotic drug resistance. The simpler models studied comprised of mixtures of POPE and POPG lipids, which form a commonly used model system for E. coli membranes. Given the important role of cardiolipin (CL) in natural membranes, a ternary model system, POPE/POPG/CL, was then considered. The results obtained in these mimetic systems were compared to those obtained for the natural systems E. coli polar and total lipid extract. DLS and fluorescence anisotropy are not commonly used to study lipid phase transitions, but it was shown that they can give useful information about the thermotropic behaviors of model systems for bacterial membranes. These two techniques provided very similar results, validating their use as methods to measure phase transitions in lipid model systems. The temperature transitions obtained from these two very different techniques and the AFM results clearly show that cardiolipin is a fundamental component to mimic bacteria membranes. The results suggest that the less commonly used ternary system is a considerably better mimic for natural E. coli membranes than binary lipid mixture.

Functionalized Dioxonaphthoimidazoliums: A Redox Cycling Chemotype with Potent Bactericidal Activities against Mycobacterium tuberculosis

“…Collectively, the fluorescence-based and genetic reporter assays corroborate the absence of stress-inducing membrane disruptive effects by the dioxonaphthoimidazolium actives. We found this puzzling given the cationic amphiphilic character of the scaffold but noted that several quinones such as menaquinone and vitamin K have been reported to be membrane stabilizers. , Thus, we reasoned that if the quinone in the dioxonaphthoimidazolium ring is membrane-stabilizing, it could negate the anticipated perturbative effects of the cationic amphiphilic scaffold, giving rise to the present observations. On a related note, CFZ is also a cationic amphiphile but has pronounced membrane disruptive effects. − Two factors could account for this intriguing difference.…”

Resisting the resistance: The antimicrobial peptide DGL13K selects for small colony variants of Staphylococcus aureus that show increased resistance to its stereoisomer LGL13K, but not to DGL13K.

“…Our genome sequencing data suggest that the chorismate/menaquinone pathway plays a role in resistance to LGL13K. Indeed, this pathway has previously been associated with activity and resistance to AMPs (45,46) and menF is part of a mutated gene complex in pexiganan-selected S. aureus (21). On the other hand, men genes were not included in the "resistome" identified upon selection of S. aureus with the endogenous AMP LL-37 or engineered LL-37 derivatives (14).…”

“…As an example, the U.S. Centers for Disease Control and Prevention estimate that over 300,000 infections and 10,000 deaths annually are attributable to methicillin-resistant S. aureus (MRSA), which is listed as a serious threat by the agency (5). WHO also lists S. aureus as a high priority pathogen for which novel antibiotics are urgently needed (6) A dozen cationic AMPs mediate the antibacterial function of human nasal fluid (7) and 45 AMPs have been identified in the oral cavity (8). Bacteria use a variety of mechanisms to defend against AMPs, including electrostatic repulsion, cell wall alteration, membrane alteration, proteolysis, protein binding and efflux pumps (9)(10)(11)(12).…”