Effects of Sterols on the Interaction of SDS, Benzalkonium Chloride, and A Novel Compound, Kor105, with Membranes

Toxic Effects of Penetrating Cations

As mitochondria are negatively charged organelles, penetrating cations are used as parts of chimeric molecules to deliver specific compounds into mitochondria. In other words, they are used as electrophilic carriers for such chemical moieties as antioxidants, dyes, etc., to transfer them inside mitochondria. However, unmodified penetrating cations affect different aspects of cellular physiology as well. In this review, we have attempted to summarise the data about the side effects of commonly used natural (e.g., berberine) and artificial (e.g., tetraphenylphosphonium, rhodamine, methylene blue) penetrating cations on cellular physiology. For instance, it was shown that such types of molecules can (1) facilitate proton transport across membranes; (2) react with redox groups of the respiratory chain; (3) induce DNA damage; (4) interfere with pleiotropic drug resistance; (5) disturb membrane integrity; and (6) inhibit enzymes. Also, the products of the biodegradation of penetrating cations can be toxic. As penetrating cations accumulate in mitochondria, their toxicity is mostly due to mitochondrial damage. Mitochondria from certain types of cancer cells appear to be especially sensitive to penetrating cations. Here, we discuss the molecular mechanisms of the toxic effects and the anti-cancer activity of penetrating cations.

Lateral membrane organization as target of an antimicrobial peptidomimetic compound

Antimicrobial resistance is one of the leading concerns in medical care. Here we study the mechanism of action of an antimicrobial cationic tripeptide, AMC-109, by combining high speed-atomic force microscopy, molecular dynamics, fluorescence assays, and lipidomic analysis. We show that AMC-109 activity on negatively charged membranes derived from Staphylococcus aureus consists of two crucial steps. First, AMC-109 self-assembles into stable aggregates consisting of a hydrophobic core and a cationic surface, with specificity for negatively charged membranes. Second, upon incorporation into the membrane, individual peptides insert into the outer monolayer, affecting lateral membrane organization and dissolving membrane nanodomains, without forming pores. We propose that membrane domain dissolution triggered by AMC-109 may affect crucial functions such as protein sorting and cell wall synthesis. Our results indicate that the AMC-109 mode of action resembles that of the disinfectant benzalkonium chloride (BAK), but with enhanced selectivity for bacterial membranes.

BCB1, a member of the acyl-coenzyme A synthetase family, regulates the morphogenesis and pathogenicity of Botrytis cinerea

Botrytis cinerea is a non-host-specific phytopathogenic fungus capable of infecting numerous cash crops. Here, we analyzed the functions of the Bcb1 gene in B. cinerea, which encodes a membrane protein belonging to the acyl-coenzyme A synthase family. Compared to the wild type, Bcb1-deletion mutants exhibited obvious morphological abnormalities, including slower vegetative growth and reduced melanin production. The absence of Bcb1 causes B. cinerea to form only small and incompletely developed infection cushions and fail to produce spores. The Bcb1 mutants displayed hypersensitivity to the membrane stressor SDS, the cell wall stressor Congo red, and the oxidative stressor H₂O₂ and increased resistance to intracellular osmotic stress caused by KCl compared to the wild-type strain. However, there were no differences in tolerance to extracellular osmotic stress caused by NaCl. The deletion of Bcb1 also caused a reduction in pathogenicity. The qRT‒PCR results showed that the genes Bcpks12 and Bcpks13, which are related to melanin biosynthesis, and Bcpg2, BcBOT2, and cutA, which are related to virulence, were downregulated in ∆Bcb1. These data suggest that BCB1 is important for conidial morphogenesis, and pathogenesis in B. cinerea.

Contribution of the Collective Excitations to the Coupled Proton and Energy Transport along Mitochondrial Cristae Membrane in Oxidative Phosphorylation System

The results of many experimental and theoretical works indicate that after transport of protons across the mitochondrial inner membrane (MIM) in the oxidative phosphorylation (OXPHOS) system, they are retained on the membrane-water interface in nonequilibrium state with free energy excess due to low proton surface-to-bulk release. This well-established phenomenon suggests that proton trapping on the membrane interface ensures vectorial lateral transport of protons from proton pumps to ATP synthases (proton acceptors). Despite the key role of the proton transport in bioenergetics, the molecular mechanism of proton transfer in the OXPHOS system is not yet completely established. Here, we developed a dynamics model of long-range transport of energized protons along the MIM accompanied by collective excitation of localized waves propagating on the membrane surface. Our model is based on the new data on the macromolecular organization of the OXPHOS system showing the well-ordered structure of respirasomes and ATP synthases on the cristae membrane folds. We developed a two-component dynamics model of the proton transport considering two coupled subsystems: the ordered hydrogen bond (HB) chain of water molecules and lipid headgroups of MIM. We analytically obtained a two-component soliton solution in this model, which describes the motion of the proton kink, corresponding to successive proton hops in the HB chain, and coherent motion of a compression soliton in the chain of lipid headgroups. The local deformation in a soliton range facilitates proton jumps due to water molecules approaching each other in the HB chain. We suggested that the proton-conducting structures formed along the cristae membrane surface promote direct lateral proton transfer in the OXPHOS system. Collective excitations at the water-membrane interface in a form of two-component soliton ensure the coupled non-dissipative transport of charge carriers and elastic energy of MIM deformation to ATP synthases that may be utilized in ATP synthesis providing maximal efficiency in mitochondrial bioenergetics.

Lipophilic Cations Rescue the Growth of Yeast under the Conditions of Glycolysis Overflow

Chemicals inducing a mild decrease in the ATP/ADP ratio are considered as caloric restriction mimetics as well as treatments against obesity. Screening for such chemicals in animal model systems requires a lot of time and labor. Here, we present a system for the rapid screening of non-toxic substances causing such a de-energization of cells. We looked for chemicals allowing the growth of yeast lacking trehalose phosphate synthase on a non-fermentable carbon source in the presence of glucose. Under such conditions, the cells cannot grow because the cellular phosphate is mostly being used to phosphorylate the sugars in upper glycolysis, while the biosynthesis of bisphosphoglycerate is blocked. We reasoned that by decreasing the ATP/ADP ratio, one might prevent the phosphorylation of the sugars and also boost bisphosphoglycerate synthesis by providing the substrate, i.e., inorganic phosphate. We confirmed that a complete inhibition of oxidative phosphorylation alleviates the block. As our system includes a non-fermentable carbon source, only the chemicals that did not cause a complete block of mitochondrial ATP synthesis allowed the initial depletion of glucose followed by respiratory growth. Using this system, we found two novel compounds, dodecylmethyl diphenylamine (FS1) and diethyl (tetradecyl) phenyl ammonium bromide (Kor105), which possess a mild membrane-depolarizing activity.

The Role of LAM Genes in the Pheromone-Induced Cell Death of S. cerevisiae Yeast

Lam1-4 proteins perform non-vesicular transport of sterols from the plasma membrane to the endoplasmic reticulum. Disruption of their function leads to an increase in the content of sterols in the plasma membrane. In mammals, homologs of Lam proteins are responsible for the internalization of plasma cholesterol. The biological role of Lam proteins in yeast remains unclear, since the strains lacking individual LAM genes do not display any pronounced phenotype. Deletion of LAM1 (YSP1) gene inhibits the regulated death of Saccharomyces cerevisiae yeast cells induced by the mating pheromone. Here, we investigated whether LAM2 also plays a role in the cell death induced by the excess of mating pheromone and assessed genetic interactions between LAM2 and genes responsible for ergosterol biosynthesis. We have shown that LAM2 deletion partially prevents pheromone-induced death of yeast cells of the laboratory strain W303, while deletions of three other LAM genes - LAM1, LAM3, and LAM4 - does not provide any additional rescuing effect. The UPC2-1 mutation in the transcription factor UPC2 gene, which leads to the excessive accumulation of sterols in the cell, promotes cell survival in the presence of the pheromone and shows additivity with the LAM2 deletion. On the contrary, LAM2 deletion stimulates pheromone-induced cell death in the laboratory strain BY4741. We have found that the deletion of ergosterol biosynthesis genes ERG2 and ERG6 reduces the effect of LAM2 deletion. Deletion of LAM2 in the Δerg4 strain lacking the gene of the last step of ergosterol biosynthesis, significantly increased the proportion of dead cells and decreased the growth rate of the yeast suspension culture even in the absence of the pheromone. We suggest that the absence of the effect of LAM2 deletion in the Δerg6 and Δerg2 strains indicates the inability of Lam2p to transport some ergosterol biosynthesis intermediates, such as lanosterol. Taken together, our data suggest that the role of Lam proteins in the regulated death of yeast cells caused by the mating pheromone is due to their effect on the plasma membrane sterol composition.

Lipid Membrane Adsorption Determines Photodynamic Efficiency of β-Imidazolyl-Substituted Porphyrins

Photosensitizers (PSs) represent a group of molecules capable of generating reactive oxygen species (ROS), such as singlet oxygen (SO); thus, they are considered to be promising agents for anti-cancer therapy. The enhancement of the photodynamic efficiency of these compounds requires increasing the PS activity in the cancer cell milieu and exactly at the target cells. In the present work, we report the synthesis, lipid membrane binding and photodynamic activity of three novel cationic PSs based on β-imidazolyl-substituted porphyrin and its Zn(II) and In(III) complexes (1H2, 1Zn and 1In). Comparison of the behavior of the investigated porphyrins at the bilayer lipid membrane (BLM) demonstrated the highest adsorption for the 1In complex and the lowest one for 1Zn. The photodynamic efficiency of these porphyrins was evaluated by determining the oxidation rate of the styryl dye, di-4-ANEPPS, incorporated into the lipid membrane. These rates were proportional to the surface density (SD) of the porphyrin molecules at the BLM and were roughly the same for all three porphyrins. This indicates that the adsorption of these porphyrins at the BLM determines their photodynamic efficiency rather than the extinction or quantum yield of singlet oxygen.