Fatty Acid Tail Research Articles

Enterococcus faecalis Readily Adapts Membrane Phospholipid Composition to Environmental and Genetic Perturbation.

The bacterial lipid membrane, consisting both of fatty acid (acyl) tails and polar head groups, responds to changing conditions through alteration of either the acyl tails and/or head groups. This plasticity is critical for cell survival as it allows maintenance of both the protective nature of the membrane as well as functioning membrane protein complexes. Bacteria that live in fatty-acid rich environments, such as those found in the human host, can exploit host fatty acids to synthesize their own membranes, in turn, altering their physiology. Enterococcus faecalis is such an organism: it is a commensal of the mammalian intestine where it is exposed to fatty-acid rich bile, as well as a major cause of hospital infections during which it is exposed to fatty acid containing-serum. Within, we employed an untargeted approach to detect the most common phospholipid species of E. faecalis OG1RF via ultra-high performance liquid chromatography high-resolution mass spectrometry (UHPLC-HRMS). We examined not only how the composition responds upon exposure to host fatty acids but also how deletion of genes predicted to synthesize major polar head groups impact lipid composition. Regardless of genetic background and differing basal lipid composition, all strains were able to alter their lipid composition upon exposure to individual host fatty acids. Specific gene deletion strains, however, had altered survival to membrane damaging agents. Combined, the enterococcal lipidome is highly resilient in response to both genetic and environmental perturbation, likely contributing to stress survival.

Structure-Activity Relationship Assessment of Sophorolipid Ester Derivatives against Model Bacteria Strains.

Sophorolipids (SLs) are glycolipids that consist of a hydrophilic sophorose head group covalently linked to a hydrophobic fatty acid tail. They are produced by fermentation of non-pathogenic yeasts such as Candida Bombicola. The fermentation products predominantly consist of the diacetylated lactonic form that coexists with the open-chain acidic form. A systematic series of modified SLs were prepared by ring opening of natural lactonic SL with n-alkanols of varying chain length under alkaline conditions and lipase-selective acetylation of sophorose primary hydroxyl groups. The antimicrobial activity of modified SLs against Gram-positive human pathogens was a function of the n-alkanol length, as well as the degree of sophorose acetylation at the primary hydroxyl sites. Modified SLs were identified with promising antimicrobial activities against Gram-positive human pathogens with moderate selectivity (therapeutic index, TI = EC50/MICB. cereus = 6–33). SL-butyl ester exhibited the best antimicrobial activity (MIC = 12 μM) and selectivity (TI = 33) among all SLs tested. Kinetic studies revealed that SL-ester derivatives kill B. cereus in a time-dependent manner resulting in greater than a 3-log reduction in cell number within 1 h at 2×MIC. In contrast, lactonic SL required 3 h to achieve the same efficiency.

The functional loss of ceramide metabolism enzymes ceramide synthase and acid sphingomyelinase on lipid metabolism and healthspan

The increase in our aging population in combination with the growing incidence of late-life conditions presents a need for research on healthy aging. Here, we present work examining the roles of sphingolipid metabolism on aging. Sphingolipids play important roles in stress response, cell survival, cell signaling, and aging. Specifically, ceramide responds to oxidative stress and recruits apoptotic proteins to the cell membrane thereby causing cell cycle arrest. Furthermore, ceramide levels increase with age, making it an important lipid mediator of aging. The objective of this study is to examine the physiological role of ceramide metabolism on aging and lipid metabolism pathways in the roundworm, Caenorhabditis elegans. To assess these mechanisms, we utilized C. elegans’ mutants lacking acid sphingomyelinase (asm-3) and ceramide synthase (hyl-2) which we previously found to be long- and short-lived respectively. We performed a lipidomic analysis to explore longitudinal changes in lipid concentrations in wild type (N2), asm-3/acid sphingomyelinase, and hyl-2/ceramide synthase worms at 1, 5, and 10 days of age. Among our samples, we detected 700 different lipids that were abundant enough in concentration for analysis. Interestingly, 10 day old hyl-2 mutants, which have a reduced life-span, showed an increased concentration of eicosapentaenoic acid (EPA), an omega-3 fatty acid that has been shown to increase with longevity in worms. Conversely, asm-3 mutants, which are long-lived animals, have reduced levels of EPA. To expand upon our lipidomic data with enzymatic findings, we utilized RT-qPCR analysis to longitudinally analyze fatty acid desaturases (fat-1 and fat-4) involved in EPA metabolism in worms. We found that fat-4 expression is reduced in 1, 5, and 10 day hyl-2 animals, suggesting that ceramide metabolism may impact fatty acid genes involved in aging. Future work will examine the role of stress response genes including superoxide dismutase (sod-3) and fatty acid tail elongases (elo-5 and elo-6) in 1, 5, and 10 day old hyl-2 and asm-3 mutants. Finally, to expand upon the current knowledge of ceramide's role in lifespan, we present data on the RNAi mediated suppression of hyl-2 in long-lived mutants including mitochondrial respiration (clk-1/coenzyme Q), insulin-like signaling (daf-2/insulin-like receptor), and dietary starvation (eat-2/mAChR). Our goal is to identify whether ceramide metabolism works within these known pathways that mediate aging. With these assays, we hope to better understand the intrinsic biochemical lipid processes associated with ceramide metabolism in aging animals.

Importance of the C12 Carbon Chain in the Biological Activity of Rhamnolipids Conferring Protection in Wheat against Zymoseptoria tritici.

The hemibiotrophic fungus Zymoseptoria tritici, responsible for Septoria tritici blotch, is currently the most devastating foliar disease on wheat crops worldwide. Here, we explored, for the first time, the ability of rhamnolipids (RLs) to control this pathogen, using a total of 19 RLs, including a natural RL mixture produced by Pseudomonas aeruginosa and 18 bioinspired RLs synthesized using green chemistry, as well as two related compounds (lauric acid and dodecanol). These compounds were assessed for in vitro antifungal effect, in planta defence elicitation (peroxidase and catalase enzyme activities), and protection efficacy on the wheat-Z. tritici pathosystem. Interestingly, a structure-activity relationship analysis revealed that synthetic RLs with a 12 carbon fatty acid tail were the most effective for all examined biological activities. This highlights the importance of the C12 chain in the bioactivity of RLs, likely by acting on the plasma membranes of both wheat and Z. tritici cells. The efficacy of the most active compound Rh-Est-C12 was 20-fold lower in planta than in vitro; an optimization of the formulation is thus required to increase its effectiveness. No Z. tritici strain-dependent activity was scored for Rh-Est-C12 that exhibited similar antifungal activity levels towards strains differing in their resistance patterns to demethylation inhibitor fungicides, including multi-drug resistance strains. This study reports new insights into the use of bio-inspired RLs to control Z. tritici.

Site-specific peroxidation modulates lipid bilayer mechanics

Peroxidation of plasma membranes, characterized by oxidative attack of lipidic carbon–carbon double-bonds in unsaturated fatty acids, has been identified as an important biochemical event in multiple pathological conditions, including neurodegenerative diseases, atherosclerosis, diabetes, preeclampsia, aging, cancer, etc. Changes to the lipid bilayer structure as a result of lipid peroxidation may lead to lipid membrane malfunction, and consequently initiate further downstream biochemical cascades. However, how lipid peroxidation modulates the mechanical properties of lipid membranes remains largely controversial. In this study, we investigate the peroxidation of lipids with polyunsaturated fatty acid tails using molecular dynamics simulations. By systematically varying the oxidation site, we find that lipid peroxidation alters the biophysical properties of bilayer membrane in a peroxidation site-specific manner. Specifically, our results suggest that peroxidation at sites in the bilayer interior disturbs and softens the membrane, whereas peroxidation at sites near the membrane–water interface results in a more ordered and stiffer membrane. Such a peroxidation site-specific modulation of lipid membrane mechanics provides an explanation for the contradictory results obtained in previous experiments. Our study paves the way for an improved understanding of the initiation of the downstream cellular dysfunction caused by lipid peroxidation.

Novel Modifications of Nonribosomal Peptides from Brevibacillus laterosporus MG64 and Investigation of Their Mode of Action.

Nonribosomal peptides (NRPs) are a class of secondary metabolites usually produced by microorganisms. They are of paramount importance in different applications, including biocontrol and pharmacy. Brevibacillus spp. are a rich source of NRPs yet have received little attention. In this study, we characterize four novel bogorol variants (bogorols I to L, cationic linear lipopeptides) and four succilins (succilins I to L, containing a succinyl group that is attached to the Orn3/Lys3 in bogorols I to L) from the biocontrol strain Brevibacillus laterosporus MG64. Further investigation revealed that the bogorol family of peptides employs an adenylation pathway for lipoinitiation, different from the usual pattern, which is based on an external ligase and coenzyme A. Moreover, the formation of valinol was proven to be mediated by a terminal reductase domain and a reductase encoded by the bogI gene. Furthermore, succinylation, which is a novel type of modification in the family of bogorols, was discovered. Its occurrence requires a high concentration of the substrate (bogorols), but its responsible enzyme remains unknown. Bogorols display potent activity against both Gram-positive and Gram-negative bacteria. Investigation of their mode of action reveals that bogorols form pores in the cell membrane of both Gram-positive and Gram-negative bacteria. The combination of bogorols and relacidines, another class of NRPs produced by B. laterosporus MG64, displays a synergistic effect on different pathogens, suggesting the great potential of both peptides as well as their producer B. laterosporus MG64 for broad applications. Our study provides a further understanding of the bogorol family of peptides as well as their applications.IMPORTANCE NRPs form a class of secondary metabolites with biocontrol and pharmaceutical potential. This work describes the identification of novel bogorol variants and succinylated bogorols (namely, succilins) and further investigates their biosynthetic pathway and mode of action. Adenylation domain-mediated lipoinitiation of bogorols represents a novel pathway by which NRPs incorporate fatty acid tails. This pathway provides the possibility to engineer the lipid tail of NRPs without identifying a fatty acid coenzyme ligase, which is usually not present in the biosynthetic gene cluster. The terminal reductase domain (TD) and BogI-mediated valinol formation and their effect on the biological activity of bogorols are revealed. Succinylation, which is rarely reported in NRPs, was discovered in the bogorol family of peptides. We demonstrate that bogorols combat bacterial pathogens by forming pores in the cell membrane. We also report the synergistic effect of two natural products (relacidine B and bogorol K) produced by the same strain, which is relevant for competition for a niche.

Characteristics and origin of intact polar lipids in soil organic matter

Membrane lipids and their related acyl and/or alkyl moieties are important biomarkers of the microbial community in environmental samples. Intact polar lipids, which are described by their lipid head groups and fatty acid tails, are major membrane components of living cells only and may therefore provide information about the living soil microbial community. However, the intact polar lipids in soil organic matter may originate from non-microbial organisms (e.g., roots, soil animals) as well as microorganisms. We report on the profiles of more than 300 membrane-derived intact polar lipids in grassland soil organic matter from sites with diverse plant communities and soil properties. The origin of the soil lipid profiles was deduced by comparisons with the intact polar lipids of plant roots, amoebae, collembolans, fungi and bacteria. In addition, we investigated the impact of plant and soil-related drivers on the composition of the intact polar lipids in soil organic matter. Soil organic matter lipid profiles were considerably more diverse and evenly distributed than the profiles of roots and soil organisms (amoebae, bacteria, collembolans and fungi). Moreover, the lipid profiles in soil organic matter had more odd-carbon numbered acyl and alkyl chains, ornithine lipids, and phospholipids with low levels of unsaturation, possibly because they are of bacterial origin. We suggest that most of the intact polar lipids in soil organic matter (45–80%) were derived from bacteria, rather than plants, fungi, or soil animals. The PE (31:0) and PE (32:1) lipids were considered as biomarkers for all bacteria, whereas PE (29:0, 29:2 and 30:0) are specific to Gram (+) bacteria and PG (33; 0, 34:1 and 36:2) and OL (36:0, 37:0, 37:1, 39:1 and 39:2) were used to identify Gram (−) bacteria. Bacterial lipids were differentiated from intact lipids of plant roots that typically contain MGDG (36:4) and MGDG (36:6), while fungi have indicative markers of PC (36:4) and PE (36:4). Thus, intact polar lipid profiles complement and advance other approaches, such as fatty acid-based analysis of soil microbial community composition, and may allow for analysis of soil food web structure.

Using stable isotope tracers to monitor membrane dynamics in C. elegans

Membranes within an animal are composed of phospholipids, cholesterol, and proteins that together form a dynamic barrier. The types of lipids that are found within a membrane bilayer impact its biophysical properties including its fluidity, permeability, and susceptibility to damage. While membrane composition is very stable in healthy adults, aberrant membrane structure is seen in a wide and varied array of diseases as well as during natural aging. Despite the wide-reaching impacts of membrane composition, there is relatively little known about how membrane landscape is established and maintained over time. In vivo biochemical modeling of membrane lipids is needed to understand how these molecules interact in their natural configurations. Here, we have described analytical methods that increase the capacity to map the dynamics of individual membrane phospholipids using different types of mass spectrometry. Specifically, we describe novel stable isotope (13C and 15N) strategies to quantify the turnover of dozens of fatty acid tails and intact phospholipids simultaneously.

Food-Poisoning Bacteria Employ a Citrate Synthase and a Type II NRPS To Synthesize Bolaamphiphilic Lipopeptide Antibiotics*.

Mining the genome of the food‐spoiling bacterium Burkholderia gladioli pv. cocovenenans revealed five nonribosomal peptide synthetase (NRPS) gene clusters, including an orphan gene locus (bol). Gene inactivation and metabolic profiling linked the bol gene cluster to novel bolaamphiphilic lipopeptides with antimycobacterial activity. A combination of chemical analysis and bioinformatics elucidated the structures of bolagladin A and B, lipocyclopeptides featuring an unusual dehydro‐β‐alanine enamide linker fused to an unprecedented tricarboxylic fatty acid tail. Through a series of targeted gene deletions, we proved the involvement of a designated citrate synthase (CS), priming ketosynthases III (KS III), a type II NRPS, including a novel desaturase for enamide formation, and a multimodular NRPS in generating the cyclopeptide. Network analyses revealed the evolutionary origin of the CS and identified cryptic CS/NRPS gene loci in various bacterial genomes.

Food‐Poisoning Bacteria Employ a Citrate Synthase and a Type II NRPS To Synthesize Bolaamphiphilic Lipopeptide Antibiotics**

AbstractMining the genome of the food‐spoiling bacterium Burkholderia gladioli pv. cocovenenans revealed five nonribosomal peptide synthetase (NRPS) gene clusters, including an orphan gene locus (bol). Gene inactivation and metabolic profiling linked the bol gene cluster to novel bolaamphiphilic lipopeptides with antimycobacterial activity. A combination of chemical analysis and bioinformatics elucidated the structures of bolagladin A and B, lipocyclopeptides featuring an unusual dehydro‐β‐alanine enamide linker fused to an unprecedented tricarboxylic fatty acid tail. Through a series of targeted gene deletions, we proved the involvement of a designated citrate synthase (CS), priming ketosynthases III (KS III), a type II NRPS, including a novel desaturase for enamide formation, and a multimodular NRPS in generating the cyclopeptide. Network analyses revealed the evolutionary origin of the CS and identified cryptic CS/NRPS gene loci in various bacterial genomes.

Partitioning of Benzoic Acid into 1,2-Dimyristoyl-sn-glycero-3-phosphocholine and Blood-Brain Barrier Mimetic Bilayers.

Using an all-atom explicit water model and replica exchange umbrella sampling simulations, we investigated the molecular mechanisms of benzoic acid partitioning into two model lipid bilayers. The first was formed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipids, whereas the second was composed of an equimolar mixture of DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine, palmitoylsphingomyelin, and cholesterol to constitute a blood-brain barrier (BBB) mimetic bilayer. Comparative analysis of benzoic acid partitioning into the two bilayers has revealed qualitative similarities. Partitioning into the DMPC and BBB bilayers is thermodynamically favorable although insertion into the former lowers the free energy of benzoic acid by approximately an additional 1 kcal mol-1. The partitioning energetics for the two bilayers is also largely similar based on the balance of benzoic acid interactions with apolar fatty acid tails, polar lipid headgroups, and water. In both bilayers, benzoic acid retains a considerable number of residual water molecules until reaching the bilayer midplane where it experiences nearly complete dehydration. Upon insertion into the bilayers, benzoic acid undergoes several rotations primarily determined by the interactions with the lipid headgroups. Nonetheless, in addition to the depth of the free energy minimum, the BBB bilayer differs from the DMPC counterpart by a much deeper location of the free energy minimum and the appearance of a high free energy barrier and positioning of benzoic acid near the midplane. Furthermore, DMPC and BBB bilayers exhibit different structural responses to benzoic acid insertion. Taken together, the BBB mimetic bilayer is preferable for an accurate description of benzoic acid partitioning.

The roles of the diversity of amphipathic lipids in shaping membranes by membrane-shaping proteins.

Lipid compositions of cells differ according to cell types and intracellular organelles. Phospholipids are major cell membrane lipids and have hydrophilic head groups and hydrophobic fatty acid tails. The cellular lipid membrane without any protein adapts to spherical shapes, and protein binding to the membrane is thought to be required for shaping the membrane for various cellular events. Until recently, modulation of cellular lipid membranes was initially shown to be mediated by proteins recognizing lipid head groups, including the negatively charged ones of phosphatidylserine and phosphoinositides. Recent studies have shown that the abilities of membrane-deforming proteins are also regulated by the composition of fatty acid tails, which cause different degrees of packing defects. The binding of proteins to cellular lipid membranes is affected by the packing defects, presumably through modulation of their interactions with hydrophobic amino acid residues. Therefore, lipid composition can be characterized by both packing defects and charge density. The lipid composition regarding fatty acid tails affects membrane bending via the proteins with amphipathic helices, including those with the ArfGAP1 lipid packing sensor (ALPS) motif and via membrane-deforming proteins with structural folding, including those with the Bin-Amphiphysin-Rvs167 (BAR) domains. This review focuses on how the fatty acid tails, in combination with the head groups of phospholipids, affect protein-mediated membrane deformation.

Morphological transition of amphiphilic block copolymer/PEGylated phospholipid complexes induced by the dynamic subtle balance interactions in the self-assembled aggregates

Abstract Recently, there has been an increasing interest in the control of morphological transition of block copolymer aggregates. Here, we report how to control the morphological transition of methoxy polyethylene glycol–poly(d,l-lactic acid) (PDLLA–MPEG) by adding 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)] (DSPE–PEG). In the aggregates formed by dialyzing DSPE–PEG/PDLLA–MPEG mixed solutions against water, the two hydrophobic fatty acid tails of DSPE–PEG will preferentially anchor to the hydrophobic segment end of PDLLA–MPEG by interdigitating between these two tails and PDLLA segments. Consequently, DSPE–PEG and PDLLA–MPEG will form “ABA” temporary supra-amphiphiles in which A represents a poly(ethylene glycol) (PEG) chain segment and B is a mixed hydrophobic segment composed of PDLLA and DSPE segments; the repulsive force derived from the PEG segments of DSPE–PEG can affect the stability of “ABA” temporary supra-amphiphiles. Our results show that the dynamic subtle balance between the number of “ABA” temporary supra-amphiphiles formed and the strength of repulsive force between the PEG segments of DSPE–PEG drives the morphological structure of DSPE–PEG/PDLLA–MPEG aggregates to change from micelles to vesicles, then to semi-vesicles and finally to mixed micelles, with increasing DSPE–PEG additions.

Structural basis for the inhibition of SARS-CoV-2 main protease by antineoplastic drug carmofur.

The antineoplastic drug carmofur is shown to inhibit the SARS-CoV-2 main protease (Mpro). Here, the X-ray crystal structure of Mpro in complex with carmofur reveals that the carbonyl reactive group of carmofur is covalently bound to catalytic Cys145, whereas its fatty acid tail occupies the hydrophobic S2 subsite. Carmofur inhibits viral replication in cells (EC50 = 24.30 μM) and is a promising lead compound to develop new antiviral treatment for COVID-19.

Stepan buys biosurfactant business

Stepan has acquired Logos Technologies’ rhamnolipid surfactant business. Rhamnolipids, which Logos makes via fermentation, feature a soluble sugar head on a fatty acid tail. They have applications in cosmetics, personal care, and bioremediation. The purchase gives Stepan intellectual property developed by Logos as well as production and analysis equipment. The lead bioprocess scientist working on the technology will move to Stepan’s R&D team in the Chicago area. Stepan plans to commercialize the surfactants within the next few years.

Use of a short, in‐class, open‐ended free response activity to assess student understanding of the cell membrane in an undergraduate physiology course

With an ever‐increasing body of information about human and animal physiology, it can be difficult for an instructor to decide what topics to focus on and what students exiting a single, stand‐alone physiology course should have learned. One valuable tool to assist in making these decisions is the set of 15 core concepts in physiology published by Michael and McFarland (Adv Physiol Educ 2011). Students in the upper division, stand‐alone physiology course at Missouri Western State University are required to have completed a freshman‐level introductory cell biology course and a sophomore‐level genetics course, but no other prerequisites are required. The prerequisite courses include discussion of the eukaryotic cell membrane and basic properties and functions of the membrane. However, many students remember the basic information about membrane structure but have difficulty relating that structure to membrane function and related topics in our physiology course, including vesicular transport, primary and secondary active transport, osmosis, and current flow across the membrane. To gain a better understanding of what students recall about the cell membrane before beginning in‐class discussion about membrane structure and function, students were given an open‐ended prompt, “What do you know about the animal cell membrane? Include structural characteristics and functions.” The students were allowed to work in small groups or alone if they preferred, and could generate their response as drawings, written statements, or both. They were given 10 minutes to construct a response. These student responses were analyzed using the conceptual framework for the “cell membrane” core concept recently published by Michael and Modell (Adv Physiol Educ 2019). 100% (19 out of 19) submissions included a drawing or description of the cell membrane as a phospholipid bilayer, and 84% of submissions included integral and peripheral membrane proteins. However, other components of the “cell membrane” conceptual framework were included much less frequently or not at all. While 58% of the responses listed diffusion or osmosis, only 32% listed active transport, and less than 10% mentioned vesicular transport, cell‐cell or cell‐matrix junctions, maintenance of solute concentration inside versus outside the cell, or cell‐to‐cell communication. No responses explicitly included simple diffusion of lipid‐soluble molecules, membrane receptors, ion channels, or physical separation/compartmentalization of the cell. Several responses had errors, such as incorrect labeled of the fatty acid tails of phospholipids as hydrophilic. This quick activity provides valuable information about what students recall from prior coursework and what concepts need to be revisited before moving into more detailed discussion of cell membrane function.

Structural characterization of Kannurin isoforms and evaluation of the role of \u03b2-hydroxy fatty acid tail length in functional specificity

The novel anti-fungal cyclic lipopeptide ‘Kannurin’ and its three structural variants produced by Bacillus cereus AK1 were previously reported from our laboratory. The present study reports unexplored structural variants of Kannurin those have functional benefits. Due to the difference in β-hydroxy fatty acid tail length, they are designated here as Kannurin A (m/z 994.67 ± 0.015), B (m/z 1008.68 ± 0.017), C (m/z 1022.69 ± 0.021), D (m/z 1036.70 ± 0.01), CL (m/z 1040.71 ± 0.02) and DL (m/z 1054.72 ± 0.01). The isoform A (m/z 994.67 ± 0.015) is the shortest cyclic form of Kannurin identified so far. In addition, CL (m/z 1040.71 ± 0.02) and DL (m/z 1054.72 ± 0.01) are the rare natural linear forms. The results of the antimicrobial assays deduced that the difference in lipid tail length of the isoforms contributes tremendous differences in their antimicrobial properties. The isoforms with short lipid tails (A and B) are more selective and potent towards bacteria, whereas the isoforms with long lipid tails (C and D) are more potent against fungi. The molecular dynamics studies and electron microscopic observations supported with circular dichroic spectroscopy analysis showed the structural confirmation and formation of aggregates of Kannurin in solution. The molecular dynamics simulation studies revealed that a single molecule of Kannurin makes enormous intra-molecular interactions and structural re-arrangements to attain stable lowest energy state in solution. When they reach a particular concentration (CMC) especially in aqueous environment, tends to form structural aggregates called ‘micelles’. With the structural information and activity relationship described in this study, it is trying to point out the sensitive structural entities that can be modified to improve the efficacy and target specificities of lipopeptide class of antibiotics.

Comparative study of gasoline, diesel and biodiesel autothermal reforming over Rh-based FeCrAl-supported composite catalyst

Catalytic autothermal reforming (ATR) of a number of hydrocarbon fuels was studied over composite RhCZ-S catalyst (0.24 wt% Rh supported on structured Ce0.75Zr0.25O2-δ-ƞ-Al2O3/FeCrAl carrier). Iso-octane and n-hexadecane as model compounds of gasoline and diesel fuel, respectively, showed similar properties in ATR process, indicating weak influence of molecular weight and branching degree of liquid alkanes on catalyst performance. Biodiesel ATR characteristics were similar to those of n-hexadecane ATR, as the utilized biodiesel predominantly contained alkanes, being products of fatty acid tail fragments hydrogenation. Even in the case of gasoline ATR, sufficient amount of monoaromatics did not influence a lot on the catalyst performance. Diesel ATR showed rather different situation: the catalyst tended to lose activity due to coking, and incomplete fuel conversion was observed. Analysis of unreacted fuel revealed bi- and polyaromatic compounds (mainly naphtalenes and antracenes) were difficult to convert.

Polyunsaturated Fatty Acid Regulation of the Acid-Sensing Ion Channels

The Acid Sensing Ion Channels (ASICS) are proton activated, voltage-insensitive, sodium channels found throughout the peripheral and central nervous systems. Tissue acidosis can occur due to injury, ischemia, and inflammation which can lead to ASIC activation. Pain that occurs with several of these conditions, including ischemia and inflammation, has previously been linked to the activation of ASICs. In addition, ASICs have been shown to be able to sense several pro-inflammatory agents that are increased under these pathophysiological conditions. The polyunsaturated fatty acid (PUFA), Arachidonic Acid, is one such molecule that potentiates ASIC isoforms 1a, 2 and 3 at concentrations reached during inflammation. Interestingly, several other PUFAs have been shown to similarly potentiate ASIC1a. However, no study has yet to elucidate the mechanism of PUFA potentiation, nor has there been a thorough investigation of the how different properties of PUFAs modulate their effect on ASICs. Here we characterized how PUFA chain length, number of double bonds, location of double bonds and head group relate to potentiation of several ASIC isoforms. First, we demonstrate that PUFAs potentiates ASICs via an alkaline shift in the pH dependence of activation. In contrast to a previous finding, we show that the head group is critical for ASIC regulation by PUFAs. PUFAs with a negatively charged head group, like Arachidonoyl Glycine, dramatically shift the pH dependence of ASIC activation while uncharged head groups like Arachidonic Acid methyl ester have no effect on channel function. In addition, we show that the position of double bonds in the fatty acid tail are important for ASIC regulation as well. Finally, mutagenesis is used to localize possible PUFA interaction sites with ASICs.

The Effects of Photosensitized Lipid Oxidation on Supported Lipid Bilayer Formation and Membrane Deformation

Lipid oxidation by reactive oxygen species (ROS) has a number of negative consequences in biology. Additionally, photosensitized lipid oxidation has been explored as a way to trigger drug release from liposomal containers. In this work we explore the effects of photosensitized lipid oxidation on the interactions of phospholipid vesicles with SiO2 surfaces. Using quartz crystal microbalance with dissipation monitoring (QCM-D), we determined that light exposure radically alters the pathway of supported lipid bilayer (SLB) formation for vesicles that contain lipid-conjugated fluorophores. Instead of the well-established two-step adsorption-rupture pathway, vesicles that have undergone photosensitized peroxidation rupture immediately upon encountering the SiO2 surface. The alteration of the vesicle rupture pathway seems to be dependent on the molecular position of the fluorescent moiety. Vesicles containing phospholipids with a BODIPY fluorophore conjugated to their fatty acid tails show the most pronounced effects. On the other hand, vesicles containing lipids with NBD conjugated to their head or tail groups show negligible differences compared to controls. We also show that antioxidants such as alpha-tocopherol (vitamin E) can attenuate the effects of photo peroxidation on the rupture pathway. Fluorescence microscopy was also used to observe lipid oxidation of a SLB, the effects of which cause membrane defects, namely membrane tubulation followed by vesiculation. Image analysis has been used to probe the characteristics of these defects, including the length of the tubes, the diameter of the subsequent vesicles, and the rate of growth of each. A direct correlation has been observed between tube length and vesicle diameter, and that the rate of growth for tubulation and vesiculation slows over time.