Kinetic modeling and optimization of the mono- and diglycerides synthesis mediated by the lipase Lipozyme® TL 100 L immobilized on clayey support.

Mono- and diglycerides play a crucial role in the food industry as multifunctional food additives and emulsifiers. Their importance stems from their unique properties, which allow them to improve the quality, texture, and stability of various food products. Here, results of the kinetic modeling of the mono- and diglycerides synthesis mediated by the lipase Lipozyme® TL 100 L immobilized on the clayey support Spectrogel® type C are reported. The support was characterized by TEM, SEM, and FTIR. Firstly, the influence of pH and lipase load on the immobilization process was analyzed, resulting in an enzymatic activity of 93.2 ± 0.7 U g-1 under optimized conditions (170.9 U g-1 of lipase and pH of 7.1). Afterward, the effects of reaction temperature and concentration of immobilized biocatalyst in the feedstock conversion were evaluated. At optimized parameters, a triglycerides conversion of 97% was obtained at 36.5 °C, 7.9 vol.% of enzyme, a glycerol to feedstock molar ratio of 2:1, and 2 h. The optimized conditions were used to determine the kinetic constants of the elementary reactions involved in the glycerolysis, where a fit superior to 0.99 was achieved between experimental values and predicted data.

Bacterial Glycolipid Acting on Protein Transport Across Membranes.

The process of protein transport across membranes involves a variety of factors and has been extensively investigated. Traditionally, proteinaceous translocons and chaperones have been recognized as crucial factors in this process. However, recent studies have highlighted the significant roles played by lipids and a glycolipid present in biological membranes in membrane protein transport. Membrane lipids can influence transport efficiency by altering the physicochemical properties of membranes. Notably, our studies have revealed that diacylglycerol (DAG) attenuates mobility in the membrane core region, leading to a dramatic suppression of membrane protein integration. Conversely, a glycolipid in Escherichia coli inner membranes, named membrane protein integrase (MPIase), enhances integration not only through the alteration of membrane properties but also via direct interactions with membrane proteins. This review explores the mechanisms of membrane protein integration mediated by membrane lipids, specifically DAG, and MPIase. Our results, along with the employed physicochemical analysis methods such as fluorescence measurements, nuclear magnetic resonance, surface plasmon resonance, and docking simulation, are presented to elucidate these mechanisms.

Interfacial behavior, gelation and foaming properties of diacylglycerols with different acyl chain lengths and isomer ratios.

Diacylglycerols (DAG) of varying chain lengths were synthesized and the acyl migrated samples with different 1,3-DAG/1,2-DAG ratios were obtained. The crystallization profile and surface adsorption differed depending on DAG structure. C12 and C14 DAGs formed small platelet- and needle-like crystals at the oil-air interface which can better reduce surface tension and pack in an ordered lamellar structure in oil. The acyl migrated DAGs with higher ratios of 1,2-DAG showed reduced crystal size and lower oil-air interfacial activity. C14 and C12 DAG oleogels exhibited higher elasticity and whipping ability with crystal shells surrounding bubbles, whereas C16 and C18 DAG oleogels had low elasticity and limited whipping ability due to the formation of aggregated needle-like crystals and loose gel network. Thus, acyl chain length dramatically influences the gelation and foaming behaviors of DAGs whereas the isomers exert little influence. This study provides basis for applying DAG of different structures in food products.

Comparison of TLC, HPLC, and direct-infusion ESI-MS methods for the identification and quantification of diacylglycerol molecular species.

Diacylglycerols (DAGs) are anabolic precursors to membrane lipid and storage triacylglycerol biosynthesis, metabolic intermediates of lipid catabolism, and potent cellular signaling molecules. The different DAG molecular species that accumulate over development or in different tissues reflect the changing aspects of cellular lipid metabolism. Consequently, an accurate determination of DAG molecular species in biological samples is essential to understand various metabolic processes and their diagnostic relevance. However, quantification of DAG molecular species in various biological samples represents a challenging task because of their low abundance, hydrophobicity, and instability. This chapter describes the most common chromatographic (TLC and HPLC) and mass spectrometry (MS) methods used to analyze DAG molecular species. In addition, we directly compared the three methods using DAG obtained by phospholipase C hydrolysis of phosphatidylcholine purified from a Nicotiana benthamiana leaf extract. We conclude that each method identified similar major molecular species, however, the exact levels of those varied mainly due to sensitivity of the technique, differences in sample preparation, and processing. This chapter provides three different methods to analyze DAG molecular species, and the discussion of the benefits and challenges of each technique will aid in choosing the right method for your analysis.

Preparation and characterization of diacylglycerol via ultrasound-assisted enzyme-catalyzed transesterification of lard with glycerol monolaurate.

The study aimed to evaluate the effect of ultrasonic pretreatment on the transesterification of lard with glycerol monolaurate (GML) using Lipozyme TL IM to synthesize diacylglycerol (DAG), and the physicochemical properties of lard, GML, ultrasonic-treated diacylglycerol (named U-DAG), purified ultrasonic-treated diacylglycerol obtained by molecular distillation (named P-U-DAG), and without ultrasonic-treated diacylglycerol (named N-U-DAG) were analyzed. The optimized ultrasonic pretreatment conditions were: lard to GML mole ratio 3:1, enzyme dosage 6 %, ultrasonic temperature 80 °C, time 9 min, power 315 W. After ultrasonic pretreatment, the mixtures reacted for 4 h in a water bath at 60 °C, the content of DAG reached 40.59 %. No significant variations were observed between U-DAG and N-U-DAG in fatty acids compositions and iodine value, while P-U-DAG had lower unsaturated fatty acids than U-DAG. Differential scanning calorimetry analysis showed that the melting and crystallization properties of DAGs prepared by ultrasonic pretreatment significantly differed from lard. FTIR spectra noted transesterification reaction from lard and GML with and without ultrasonic pretreatment would not change the structure of lard. However, thermogravimetric analysis proved that N-U-DAG, U-DAG, and P-U-DAG had lower oxidation stability than lard. The higher the content of DAG, the faster the oxidation speed.

Direct Chiral Supercritical Fluid Chromatography-Mass Spectrometry Analysis of Monoacylglycerol and Diacylglycerol Isomers for the Study of Lipase-Catalyzed Hydrolysis of Triacylglycerols.

The fast and selective separation method of intact monoacylglycerol (MG) and diacylglycerol (DG) isomers using chiral supercritical fluid chromatography-mass spectrometry (SFC-MS) was developed and employed to study lipase selectivity in the hydrolysis of triacylglycerols (TGs). The synthesis of 28 enantiomerically pure MG and DG isomers was performed in the first stage using the most commonly occurring fatty acids in biological samples such as palmitic, stearic, oleic, linoleic, linolenic, arachidonic, and docosahexaenoic acids. To develop the SFC separation method, different chromatographic conditions such as column chemistry, mobile phase composition and gradient, flow rate, backpressure, and temperature were carefully assessed. Our SFC-MS method used a chiral column based on a tris(3,5-dimethylphenylcarbamate) derivative of amylose and neat methanol as a mobile phase modifier, which provides baseline separation of all the tested enantiomers in 5 min. This method was used to evaluate hydrolysis selectivity of lipases from porcine pancreas (PPL) and Pseudomonas fluorescens (PFL) using nine TGs differing in acyl chain length (14-22 carbon atoms) and number of double bonds (0-6) and three DG regioisomer/enantiomers as hydrolysis intermediate products. PFL exhibited preference of the fatty acyl hydrolysis from the sn-1 position of TG more pronounced for the substrates with long polyunsaturated acyls, while PPL did not show considerable stereoselectivity to TGs. Conversely, PPL preferred hydrolysis from the sn-1 position of prochiral sn-1,3-DG regioisomer, whereas PFL exhibited no preference. Both lipases showed selectivity for the hydrolysis of outer positions of DG enantiomers. The results show complex reaction kinetics of lipase-catalyzed hydrolysis given by different stereoselectivities for substrates.

Structure-guided preparation of fuctional oil rich in 1,3-diacylglycerols and linoleic acid from Camellia oil by combi-lipase.

BACKGROUND: Diacylglycerol (DAG)-enriched oil has been attracting attention because of its nutritional benefits and biological functions, although the composition of its various free fatty acids (FFAs) and an unclear relationship between substrate and yield make it difficult to be identified and qualified with respect to its production. In the present study, linoleic acid-enriched diacylglycerol (LA-DAG) was synthesized and enriched from Camellia oil by the esterification process using the combi-lipase Lipozyme TL IM/RM IM system. RESULTS: The relationship between FFA composition and DAG species productivity was revealed. The results showed that heterogeneous FFA with a major constituent (more than 50%) exhibited higher DAG productivity and inhibited triacylglycerol productivity compared to homogeneous constituents. Joint characterization by high-performance liquid chromatography-evaporative light scattering detection, gas chromatography-mass spectrometry and ultra-performance liquid chromatography-heated electrospray ionization-tandem mass spectrometry identified that DAG components contained dilinoleic acid acyl glyceride, linoleyl-oleyl glyceride and dioleic acid acyl glyceride in esterification products. Under the optimum conditions, 60.4% 1,3-DAG and 61.3% LA-DAG in the crude product at 1 h reaction were obtained, and further purified to 81.7% LA-DAG and 94.7% DAG via silica column chromatography. CONCLUSION: The present study provides a guideline for the identification of DAG species, as well as a structure-guided preparation method of DAG-enriched oils via the cost-effective combi-lipase. © 2022 Society of Chemical Industry.

Immobilization of Candida antarctica Lipase A onto Macroporous Resin NKA-9: Esterification and Glycerolysis Performance Study.

In this study, lipase A from Candida antarctica (CALA) was immobilized onto the macroporous resin NKA-9. Immobilization conditions (pH, time and CALA concentration) were studied, enzymatic activity and immobilization efficiency (IE) up to 968.89 U/g and 53.19% were respectively obtained under optimal conditions (immobilization pH 5.0, time 5 h and CALA concentration at 30 mg/mL). Then, the NKA-9 supported CALA (CALA@NKA-9) samples were used to catalyze glycerolysis in solvent-free system. With 0.25 g of the present CALA@NKA-9 (soybean oil 3.52 g and glycerol 0.184 g) and after 12 h reaction at 50 °C, diacylglycerols (DAG) content up to 64.37% and triacylglycerols (TAG) conversion at 83.33% were obtained. The relationship between temperature and TAG conversion was LnV 0 = 13.9310-6.4212/T for CALA@NKA-9. Meanwhile, the activation energy (Ea) of CALA@NKA-9 was calculated to be 53.39 kJ/mol. In addition, reusability in the glycerolysis reaction was also evaluated, and 57.82% of the initial glycerolysis activity was retained after 9 consecutive applications. Furthermore, the CALA@NKA-9 was also used to catalyze the esterification (esterification of fatty acids with glycerol), however, the present CALA@NKA-9 cannot initiate the esterification. Therefore, the present CALA@NKA-9 is shown to be potential for DAG production through glycerolysis reaction.

Exploring the AlphaFold Predicted Conformational Properties of Human Diacylglycerol Kinases.

Diacylglycerol kinases (DGKs) are important enzymes in molecular membrane biology, as they can lower the concentration of diacylglycerol through phosphorylation while at the same time producing phosphatidic acid. Dysfunction of DGK is linked with multiple diseases including cancer and autoimmune disorders. Currently, the high-resolution structures have not been determined for any of the 10 human DGK paralogs, which has made it difficult to gain a more complete understanding of the enzyme's mechanism of action and regulation. In the present study, we have taken advantage of the significant developments in protein structural prediction technology by artificial intelligence (i.e., Alphafold 2.0), to conduct a comprehensive investigation on the properties of all 10 human DGK paralogs. Structural alignment of the predictions reveals that the C1, catalytic, and accessory domains are conserved in their spatial arrangement relative to each other, across all paralogs. This suggests a critical role played by this domain architecture in DGK function. Moreover, docking studies corroborate the existence of a conserved ATP-binding site between the catalytic and accessory domains. Interestingly, the ATP bound to the interdomain cleft was also found to be in proximity of the conserved glycine-rich motif, which in protein kinases has been suggested to function in ATP binding. Lastly, the spatial arrangement of DGK, with respect to the membrane, reveals that most paralogs possess a more energetically favorable interaction with curved membranes. In conclusion, AlphaFold predictions of human DGKs provide novel insights into the enzyme's structural and functional properties while also paving the way for future experimentation.

Human Diacylglycerol Kinase ε N-Terminal Segment Regulates the Phosphatidylinositol Cycle, Controlling the Rate but Not the Acyl Chain Composition of Its Lipid Intermediates.

Diacylglycerol kinase ε (DGKε), an enzyme of the phosphatidylinositol (PI) cycle, bears a highly conserved hydrophobic N-terminal segment, which was proposed to anchor the enzyme into the membrane. However, the importance of this segment to the DGKε function remains to be determined. To address this question, it is here reported an in silico and in vitro combined research strategy. Capitalizing on the AlphaFold 2.0 predicted structure of human DGKε, it is shown that its hydrophobic N-terminal segment anchors it into the membrane via a transmembrane α-helix. Coarse-grained based elastic network model studies showed that a conformational change in the hydrophobic N-terminal segment determines the proximity between the active site of DGKε and the membrane-water interface, likely regulating its kinase activity. In vitro studies with a purified DGKε construct lacking the hydrophobic N-terminal segment (His-SUMO*-Δ50-DGKε) corroborated the role of the N-terminus in regulating DGKε enzymatic properties. The comparison between the enzymatic properties of DGKε and His-SUMO*-Δ50-DGKε showed that the conserved N-terminal segment markedly inhibits the enzyme activity and its sensitivity to membrane intrinsic negative curvature, while also playing a role in the modulation of the enzyme by phosphatidylserine. On the other hand, this segment did not strongly affect its diacylglycerol acyl chain specificity, the modulation of the enzyme by membrane morphological changes, or the activation by phosphatidic acid-rich lipid domains. Hence, these results suggest that the conservation of the hydrophobic N-terminal segment of DGKε throughout evolution guaranteed not only membrane anchorage but also an efficient and elegant manner to regulate the rate of the PI cycle.

Water-in-oil emulsions enriched with alpha-linolenic acid in diacylglycerol form: Stability, formation mechanism and in vitro digestion analysis.

This study developed an alpha-linolenic acid (ALA) supplement with emulsion form using ALA-rich diacylglycerol (ALA-DAG) and ALA-DAG stearin (DAG-SF) as a new source of ALA and emulsifier. Stable, commercial surfactant-free W/O emulsions with 90 wt% oil phase (including DAG-SF and ALA-DAG with 10:90 - 20:80 wt ratio) was fabricated. Microstructure and Raman spectra revealed that the compact crystal networks and high amounts of solid acyl chains were responsible for high emulsion stability. These emulsions exhibited good potential in improving the ALA nutritional status (with ALA release level of 60.49% - 62.98%). Furthermore, the emulsifier-to-oil ratio greatly impacted the emulsion texture (solid-like or liquid-like) and emulsions showed great oxidation stability (2.80 - 3.09 meq/kg lipid of peroxide value at 6th week). The tunable texture and high oxidation stability make this emulsion system useful for a wide range of food products. This developed emulsion system could provide valuable information for other important fatty acids supplement.

Stabilisation of oleofoams by lauric acid and its glycerol esters.

Four types of pure lipid, namely lauric acid (LA), glycerol monolaurate (MAG), diglycerol laurate (DAG) and triglyceride laurate (TAG) were used to prepare oleofoams. The relationship between crystal profiles and their performance in oleofoams was established. DAG formed small needle-like crystals while MAG formed large flake-like crystals in oleogels, and crystal shells around air bubbles were observed in LA-, MAG- and DAG-based oleofoams. LA and DAG displayed higher over-run whereas DAG-stabilised foam possessed smaller bubbles and higher physical stability due to the presence of small ß and ß' crystals. Upon heating, DAG and TAG-based foams showed varying extents of oil drainage indicating the crystals were distributed in a different manner. Therefore, DAG was shown to be an excellent gelator in the fabrication of ultra-stable oleofoams. This work extends the lipid varieties with nutritional features and allows a better understanding on the stabilization mechanisms of lauric acid lipids in oleofoams.

Structural anatomy of Protein Kinase C C1 domain interactions with diacylglycerol and other agonists.

Diacylglycerol (DAG) is a versatile lipid whose 1,2-sn-stereoisomer serves both as second messenger in signal transduction pathways that control vital cellular processes, and as metabolic precursor for downstream signaling lipids such as phosphatidic acid. Effector proteins translocate to available DAG pools in the membranes by using conserved homology 1 (C1) domains as DAG-sensing modules. Yet, how C1 domains recognize and capture DAG in the complex environment of a biological membrane has remained unresolved for the 40 years since the discovery of Protein Kinase C (PKC) as the first member of the DAG effector cohort. Herein, we report the high-resolution crystal structures of a C1 domain (C1B from PKCδ) complexed to DAG and to each of four potent PKC agonists that produce different biological readouts and that command intense therapeutic interest. This structural information details the mechanisms of stereospecific recognition of DAG by the C1 domains, the functional properties of the lipid-binding site, and the identities of the key residues required for the recognition and capture of DAG and exogenous agonists. Moreover, the structures of the five C1 domain complexes provide the high-resolution guides for the design of agents that modulate the activities of DAG effector proteins.

Coupling Stable Isotope Labeling and Liquid Chromatography-Trapped Ion Mobility Spectrometry-Time-of-Flight-Tandem Mass Spectrometry for De Novo Mosquito Ovarian Lipid Studies.

There is a need to better understand lipid metabolism during mosquito ovarian development. Lipids are the major source of energy supporting ovarian follicles development in mosquitoes. In this paper, we describe the complementary use of stable isotope labeling (SIL) and high-resolution mass spectrometry-based tools for the investigation of de novo triglycerides (TG) and diglycerides (DG) during the ovarian previtellogenic (PVG) stage (4-6 days posteclosion) of female adult Aedes aegypti. Liquid chromatography coupled to high-resolution trapped ion mobility spectrometry-parallel accumulation sequential fragmentation-time-of-flight tandem mass spectrometry (LC-TIMS-PASEF-TOF MS/MS) allowed the separation and quantification of nonlabeled and 2H/13C-labeled TG and DG species. Three SIL strategies were evaluated (H2O/2H2O with 50:50 and 95:5 mixtures, 13C-sucrose, and 13C-glucose). Results showed wide applicability with no signs of lipid ovarian impairment by SIL induced toxicity. The analytical workflow based on LC-TIMS-TOF MS/MS provided high confidence and high reproducibility for lipid DG and TG identification and SIL incorporation based on their separation by retention time (RT), collision cross section (CCS), and accurate m/z. In addition, the SIL fatty acid chain incorporation was evaluated using PASEF MS/MS. The 2H/13C incorporation into the mosquito diet provided information on how TG lipids are consumed, stored, and recycled during the PVG stage of ovarian development.

Influence of ceramide on lipid domain stability studied with small-angle neutron scattering: The role of acyl chain length and unsaturation.

Ceramides and diacylglycerols are groups of lipids capable of nucleating and stabilizing ordered lipid domains, structures that have been implicated in a range of biological processes. Previous studies have used fluorescence reporter molecules to explore the influence of ceramide acyl chain structure on sphingolipid-rich ordered phases. Here, we use small-angle neutron scattering (SANS) to examine the ability of ceramides and diacylglycerols to promote lipid domain formation in the well-characterized domain-forming mixture DPPC/DOPC/cholesterol. SANS is a powerful, probe-free technique for interrogating membrane heterogeneity, as it is differentially sensitive to hydrogen's stable isotopes protium and deuterium. Specifically, neutron contrast is generated through selective deuteration of lipid species, thus enabling the detection of nanoscopic domains enriched in deuterated saturated lipids dispersed in a matrix of protiated unsaturated lipids. Using large unilamellar vesicles, we found that upon replacing 10 mol% DPPC with either C16:0 or C18:0 ceramide, or 16:0 diacylglycerol (dag), lipid domains persisted to higher temperatures. However, when DPPC was replaced with short chain (C6:0 or C12:0) or very long chain (C24:0) ceramides, or ceramides with unsaturated acyl chains of any length (C6:1(3), C6:1(5), C18:1, and C24:1), as well as C18:1-dag, lipid domains were destabilized, melting at lower temperatures than those in the DPPC/DOPC/cholesterol system. These results show how ceramide acyl chain length and unsaturation influence lipid domains and have implications for how cell membranes might modify their function through the generation of different ceramide species.

Diacylglycerol pre-emulsion prepared through ultrasound improves the gel properties of golden thread surimi.

This study determined the influence of diacylglycerol (DAG) pre-emulsion on the gel properties and microstructure of golden thread surimi gels. DAG emulsion stabilized using sodium caseinate was pre-emulsified through ultrasound. The average particle size of DAG pre-emulsion decreased from 1324.15 nm to 41.19 nm, with notable improvements in apparent viscosity and storage stability. The surimi gels with different amounts (0%, 1%, 3%, 5%, and 7% w/w) of DAG pre-emulsion were prepared under heat induction. The whiteness of the composite gels markedly increased with the incorporation of DAG pre-emulsion. The peak T22 value of immobilized water, the gel strength, and water-holding capacity increased gradually, but it slightly decreased with the addition of 7% pre-emulsion. The curve of G' and G″ kept climbing as the concentration of pre-emulsion, and the microstructure of the gel network tended to become denser and more orderly. Principal component analysis (PCA) of electronic nose results showed that the surimi gels containing pre-emulsion could be clearly distinguished from the control group. In conclusion, the addition of 5% DAG pre-emulsion to surimi not only improved gel properties to the highest extent but also be compensated for lipid loss during the rinsing of surimi.

PIP3 abundance overcomes PI3K signaling selectivity in invadopodia.

PI3Kß is required for invadopodia-mediated matrix degradation by breast cancer cells. Invadopodia maturation requires GPCR activation of PI3Kß and its coupling to SHIP2 to produce PI(3,4)P2 . We now test whether selectivity for PI3Kß is preserved under conditions of mutational increases in PI3K activity. In breast cancer cells where PI3Kß is inhibited, short-chain diC8-PIP3 rescues gelatin degradation in a SHIP2-dependent manner; rescue by diC8-PI(3,4)P2 is SHIP2-independent. Surprisingly, the expression of either activated PI3Kß or PI3Kα mutants rescued the effects of PI3Kß inhibition. In both cases, gelatin degradation was SHIP2-dependent. These data confirm the requirement for PIP3 conversion to PI(3,4)P2 for invadopodia function and suggest that selectivity for distinct PI3K isotypes may be obviated by mutational activation of the PI3K pathway.

Certain, but Not All, Tetraether Lipids from the Thermoacidophilic Archaeon Sulfolobus acidocaldarius Can Form Black Lipid Membranes with Remarkable Stability and Exhibiting Mthk Channel Activity with Unusually High Ca2+ Sensitivity.

Bipolar tetraether lipids (BTL) have been long thought to play a critical role in allowing thermoacidophiles to thrive under extreme conditions. In the present study, we demonstrated that not all BTLs from the thermoacidophilic archaeon Sulfolobus acidocaldarius exhibit the same membrane behaviors. We found that free-standing planar membranes (i.e., black lipid membranes, BLM) made of the polar lipid fraction E (PLFE) isolated from S. acidocaldarius formed over a pinhole on a cellulose acetate partition in a dual-chamber Teflon device exhibited remarkable stability showing a virtually constant capacitance (~28 pF) for at least 11 days. PLFE contains exclusively tetraethers. The dominating hydrophobic core of PLFE lipids is glycerol dialky calditol tetraether (GDNT, ~90%), whereas glycerol dialkyl glycerol tetraether (GDGT) is a minor component (~10%). In sharp contrast, BLM made of BTL extracted from microvesicles (Sa-MVs) released from the same cells exhibited a capacitance between 36 and 39 pF lasting for only 8 h before membrane dielectric breakdown. Lipids in Sa-MVs are also exclusively tetraethers; however, the dominating lipid species in Sa-MVs is GDGT (>99%), not GDNT. The remarkable stability of BLMPLFE can be attributed to strong PLFE-PLFE and PLFE-substrate interactions. In addition, we compare voltage-dependent channel activity of calcium-gated potassium channels (MthK) in BLMPLFE to values recorded in BLMSa-MV. MthK is an ion channel isolated from a methanogenic that has been extensively characterized in diester lipid membranes and has been used as a model for calcium-gated potassium channels. We found that MthK can insert into BLMPLFE and exhibit channel activity, but not in BLMSa-MV. Additionally, the opening/closing of the MthK in BLMPLFE is detectable at calcium concentrations as low as 0.1 mM; conversely, in diester lipid membranes at such a low calcium concentration, no MthK channel activity is detectable. The differential effect of membrane stability and MthK channel activity between BLMPLFE and BLMSa-MV may be attributed to their lipid structural differences and thus their abilities to interact with the substrate and membrane protein. Since Sa-MVs that bud off from the plasma membrane are exclusively tetraether lipids but do not contain the main tetraether lipid component GDNT of the plasma membrane, domain segregation must occur in S. acidocaldarius. The implication of this study is that lipid domain formation is existent and functionally essential in all kinds of cells, but domain formation may be even more prevalent and pronounced in hyperthermophiles, as strong domain formation with distinct membrane behaviors is necessary to counteract randomization due to high growth temperatures while BTL in general make archaea cell membranes stable in high temperature and low pH environments whereas different BTL domains play different functional roles.

Tailored rigidity of W/O Pickering emulsions using diacylglycerol-based surface-active solid lipid nanoparticles.

Pickering water-in-oil (W/O) emulsions were fabricated by using medium-long chain diacylglycerol (MLCD)-based solid lipid nanoparticles (SLNs) and the connection between the characteristics of the SLNs and the colloidal stability of the emulsions was established. Via melt-emulsification and ultrasonication, MLCD-based SLNs with particle sizes of 120-300 nm were obtained with or without other surfactants. The particle size of the SLNs was influenced by the chemical properties of the surfactants, and surfactants decreased the contact angle of SLNs at the oil-water interface. Gelation was observed in SLNs modified by sodium stearoyl lactylate and lecithin, whereas the addition of Tween 20 resulted in a homogeneous SLN solution. The adsorption of surfactants onto SLN surfaces caused the production of higher amounts of α crystals accompanied by delayed crystallization onset which contributed to the reduction of particle size, interfacial tension and oil wetting ability. The W/O emulsions with higher rigidity and physical stability can be obtained by varying surfactant types and by increasing SLN mass ratios to 60%, whereby more SLNs are adsorbed at the droplet surface as a Pickering stabilizer. This study provides useful insights for the development of diacylglycerol-based SLNs and Pickering W/O emulsions which have great potential for food, cosmetic and pharmaceutical applications.

Unveiling Glycerolipid Fragmentation by Cryogenic Infrared Spectroscopy.

Mass spectrometry is routinely employed for structure elucidation of molecules. Structural information can be retrieved from intact molecular ions by fragmentation; however, the interpretation of fragment spectra is often hampered by poor understanding of the underlying dissociation mechanisms. For example, neutral headgroup loss from protonated glycerolipids has been postulated to proceed via an intramolecular ring closure but the mechanism and resulting ring size have never been experimentally confirmed. Here we use cryogenic gas-phase infrared (IR) spectroscopy in combination with computational chemistry to unravel the structures of fragment ions and thereby shed light on elusive dissociation mechanisms. Using the example of glycerolipid fragmentation, we study the formation of protonated five-membered dioxolane and six-membered dioxane rings and show that dioxolane rings are predominant throughout different glycerolipid classes and fragmentation channels. For comparison, pure dioxolane and dioxane ions were generated from tailor-made dehydroxyl derivatives inspired by natural 1,2- and 1,3-diacylglycerols and subsequently interrogated using IR spectroscopy. Furthermore, the cyclic structure of an intermediate fragment occurring in the phosphatidylcholine fragmentation pathway was spectroscopically confirmed. Overall, the results contribute substantially to the understanding of glycerolipid fragmentation and showcase the value of vibrational ion spectroscopy to mechanistically elucidate crucial fragmentation pathways in lipidomics.