An atomistic model of STX is developed and it is demonstrated that STX significantly increases lipid packing and acyl chain order of STX–PG bilayer mixtures, and reduces the gel-to-liquid crystalline phase transition temperature, indicating a general stabilizing effect for the fluid phase of PG lipids of varying length.
Abstract
Staphyloxanthin (STX) is a carotenoid synthesized by the human pathogen Staphylococcus aureus. The golden color of this bacterium is due to this carotenoid. STX protects Staphylococcus aureus from oxidative stress by scavenging free radical species. Furthermore, STX has been shown to mechanically strengthen the Staphylococcus aureus membrane and to form microdomains that recruit antibiotic-resistance factors. Thus, inhibition of STX is a promising strategy for intervening against multidrug-resistant strains of this pathogen. However, the molecular mechanisms by which STX regulates the membrane structure and function of Staphylococcus aureus remain unclear. More specifically, the localization of STX within phosphatidylglycerol (PG) bilayers, the primary phospholipid of this bacterium’s membrane, and how this localization drives macroscopic biophysical changes remain unresolved questions. Here, we addressed this issue by integrating molecular dynamics (MD) simulations, X-ray scattering experiments, and fluorescence spectroscopy. We developed an atomistic model of STX, which was validated against X-ray scattering data and which is suitable for all-atom MD simulations. We demonstrate that STX significantly increases lipid packing and acyl chain order of STX–PG bilayer mixtures. In addition, STX self-assembles into clusters, where the long and rigid conjugated triterpenoid chain interdigitates across both leaflets, modifying locally the density of the surrounding PG molecules. These findings provide a molecular explanation to the reduced headgroup spacing and core dynamics observed in fluorescence experiments and are consistent with the formation of structurally-distinct STX-enriched microdomains. Notably, STX reduces the gel-to-liquid crystalline phase transition temperature, indicating a general stabilizing effect for the fluid phase of PG lipids of varying length. Overall, our findings provide molecular insights into how STX enhances membrane mechanical integrity. It will be highly interesting to establish how the membrane remodeling effects observed here connect with STX’s dual roles, acting as an antioxidant and preventing pore formation and other mechanical perturbations induced by antimicrobial molecules.
Staphylococcus aureus (S. aureus) is a prominent foodborne pathogen that poses a continuous threat to global public health and food safety due to its possession of a variety of toxins and its multidrug resistance. Medium-chain fatty acids (MCFAs), notably lauric acid (LA), exhibit strong antimicrobial properties, but their application is heavily constrained by poor water solubility. In this study, optimized LA emulsions stabilized by chitosan (CS) and polyvinyl alcohol (PVA) were evaluated for their antibacterial activity and detailed mode of action against S. aureus ATCC 6538. The antibacterial activities were evaluated by the maximum inhibition zone, with the 20 CS-PVA/DLTA-LA formulation exhibiting stable dispersion and potent antibacterial activity at 1%. The underlying antibacterial mechanisms against S. aureus were specifically focused on cell membranes and peptidoglycan. Therein, the binding of emulsion droplets to the anionic bacterial surface was driven by electrostatic attraction. Membrane degradation was also observed with membrane dysfunctions involving membrane depolarization, increased permeability, and fluidity reduction triggered by their subsequent insertion into the lipid bilayer, which may cause cell dysmetabolism, disintegration, and eventual cell death. Overall, these findings substantiate that LA emulsions disrupt S. aureus by operating potentially multi-targeted effects involving cell membrane disruption and peptidoglycan interference, offering a promising alternative approach warranting further investigation for foodborne pathogen control.
Peipei Ma, Run-run Zhang, Chen Li et al.· Foods· 0 citations
Phenol-soluble modulin α1 (PSMα1) is a cytolytic peptide secreted by Staphylococcus aureus that contributes to host-cell damage and biofilm stability, yet the relationship between its assembly behavior and function remains incompletely understood. Here, we combine cellular assays, molecular spectroscopy, and high-resolution structural approaches to elucidate how environmental conditions govern PSMα1 activity and supramolecular organization. Live-cell imaging and cytotoxicity assays show that PSMα1 accumulates at the plasma membrane of human cells prior to membrane permeabilization, linking membrane association to cytotoxic outcomes. This process is strongly attenuated by epigallocatechin gallate (EGCG). Cryogenic electron microscopy (cryo-EM) reveals two polymorphic canonical amyloid fibril architectures that share a conserved hydrophobic core and protofilament interface. In parallel, we identify pH as a key determinant of PSMα1 assembly pathways, driving a bifurcation between cross-β amyloid fibrils at extreme acidic and alkaline conditions and heterogeneous, long-lived, thermally stable α-helical nanotubular assemblies at acidic, near-neutral, and slightly alkaline conditions, which act as transient intermediates under highly acidic conditions. Together, these findings demonstrate that PSMα1 is not a single amyloid structure but a condition-dependent structural system in which environmental cues dictate assembly, membrane interaction, and cytotoxic function. This work provides a framework for understanding how polymorphic assembly of bacterial virulence peptides interfaces with host-cell interactions and suggests new avenues for targeting PSM-mediated pathogenicity. Statement of significance Staphylococcus aureus causes severe infections and uses the peptide PSMα1 to damage host cells and strengthen protective biofilms. Like many disease-associated proteins, PSMα1 self-assembles into amyloid fibrils, though their role in virulence remains unclear. We show that PSMα1 does not adopt a single architecture. Instead, environmental changes, such as those at infection sites, drive the peptide into distinct assemblies, including cross-β amyloid fibrils and unexpectedly stable nanotubes with α-helical features. Live-cell imaging shows PSMα1 accumulates at the plasma membrane before cell death, and that epigallocatechin gallate reduces membrane association and toxicity. These findings show that bacterial virulence can be regulated through environmentally controlled transitions between protein assemblies, identifying membrane accumulation as a promising anti-virulence target.
Sambhasan Banerjee, V. Skoryk, Bader Rayan et al.· bioRxiv· 0 citations
This study for the first time constructs a complete temporal mechanism chain from initial membrane damage and rapid metabolic disorder to downstream cellular dysfunction for the CAR-ε-PL synergy, providing a novel theoretical basis for developing natural antimicrobial strategies in food preservation.
Xiangyu Zang, Chen Du, Shuai Wan et al.· RSC Advances· 0 citations
The present study suggests that photo-responsive polypeptide PNFs represent a promising and versatile therapeutic strategy for combating antibiotic-resistant bacterial infections, owing to their dual functional capabilities.
Sangita Rajwar, C. Kumar, Shreya Ghosh et al.· ACS Applied Bio Materials· 0 citations
A model in which the MbcS-dependent pathway enables S. aureus to scavenge BCFA precursors under nutrient-limited conditions, providing a competitive advantage in polymicrobial environments is supported.
Marcelle C. dos Santos Ferreira, T. Stephens, Shaun R. Brinsmade· Journal of Bacteriology· 0 citations
It is demonstrated for the first time that amyloid formation, similar to MV production, is regulated by environmental stresses, and a potential role for this complex in the environmental adaptation of S. aureus is suggested.
Zhuang Zhu, Jinxi Yue, Yalan Feng et al.· Microbial Pathogenesis· 0 citations