Plasmonic Resonant Nanoantennas Induce Changes in the Shape and the Intensity of Infrared Spectra of Phospholipids

Surface enhanced infrared absorption spectroscopic studies (SEIRAS) as a technique to study biological molecules in extremely low concentrations is greatly evolving. In order to use the technique for identification of the structure and interactions of such biological molecules, it is necessary to identify the effects of the plasmonic electric-field enhancement on the spectral signature. In this study the spectral properties of 1,2-Dipalmitoyl-sn-glycero-3 phosphothioethanol (DPPTE) phospholipid immobilized on gold nanoantennas, specifically designed to enhance the vibrational fingerprints of lipid molecules were studied. An AFM study demonstrates an organization of the DPPTE phospholipid in bilayers on the nanoantenna structure. The spectral data were compared to SEIRAS active gold surfaces based on nanoparticles, plain gold and plain substrate (Si) for different temperatures. The shape of the infrared signals, the peak positions and their relative intensities were found to be sensitive to the type of surface and the presence of an enhancement. The strongest shifts in position and intensity were seen for the nanoantennas, and a smaller effect was seen for the DPPTE immobilized on gold nanoparticles. This information is crucial for interpretation of data obtained for biological molecules measured on such structures, for future application in nanodevices for biologically or medically relevant samples.

Application of MCR-ALS with EFA on FT-IR spectra of lipid bilayers in the assessment of phase transition temperatures: Potential for discernment of coupled events

Temperature-dependent transmission FT-IR spectroscopy and DSC measurements were conducted on lipid multibilayers constituted from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. Lipid multibilayers made from 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, which do not form a ripple phase, were examined as a reference. Spectra were analyzed using multivariate curve resolution technique with alternating least squares and evolving factor analysis (MCR-ALS with EFA) and lipid phase transition temperatures were determined. Polar parts of lipid molecules exert greater response on a ripple phase formation than non-polar ones. However, vibrational signatures of hydrocarbon chains with intramolecular origins display certain qualitative differences that pave the way for future work oriented on uncoupling the events that drive ripple phase formation.

Influence of phenothiazine molecules on the interactions between positively charged poly-l-lysine and negatively charged DPPC/DPPG membranes

Phenothiazines are very effective antipsychotic drugs, which also have anticancer and antimicrobial activities. Despite being used in human treatment, the molecular mechanism of the biological actions of these molecules is not yet understood in detail. The role of the interactions between phenothiazines and proteins or lipid membranes has been much discussed. Herein, fourier-transform infrared (FTIR) spectroscopic studies were used to investigate the effect of three phenothiazines: fluphenazine (FPh); chlorpromazine (ChP); and propionylpromazine (PP) on the structures of a positively charged poly-l-lysine (PLL) peptide, a negatively charged dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylglycerol (DPPC/DPPG) membrane, and on the mutual interactions between electrostatically associated PLL molecules and DPPC/DPPG membranes. Phenothiazine-induced alterations in the secondary structure of PLL, the conformational state (trans/gauche) of the hydrocarbon lipid chains, and the hydration of the DPPC/DPPG membrane interface were studied on the basis of amide I' vibrations, antisymmetric and symmetric stretching vibrations of the CH₂ groups of the lipid hydrocarbon chains (ν_sCH₂), and stretching vibrations of the lipid C=O groups (νC = O), respectively. It was shown that in the presence of negatively charged DPPC/DPPG membranes, the phenothiazines were able to modify the secondary structure of charged PLL molecules. Additionally, the effect of PLL on the structure of DPPC/DPPG membranes was also altered by the presence of the phenothiazine molecules.

Effect of phenothiazine compounds on the secondary structure and fibrillogenesis of poly-l-lysine

Phenothiazine molecules are effective and commonly used antipsychotic drugs, especially in the treatment of schizophrenia. However, they produce strong extrapyramidal side-effects manifested by drug-induced parkinsonism. Because Parkinson's disease as a neurodegenerative illness is associated with the formation of amyloid fibrils in neuronal cells, it is postulated that the development of phenothiazine-induced parkinsonism may be related to the phenothiazine-induced formation of fibrillar aggregates. The effect of phenothiazine compounds (fluphenazine (FPh), chlorpromazine (ChP) and propionylpromazine (PP)) on the fibrillogenesis of poly-l-lysine (PLL) was studied using Fourier-transform infrared (FTIR) spectroscopy supported by principal component analysis (PCA), vibrational circular dichroism (VCD), transmission electron microscopy (TEM) and Congo red binding assay. The fibrillogenesis of PLL is accompanied by fibril formation with charged or uncharged polypeptides with PPII (polyproline-like extended helix), α-helix or β-sheet conformations. All of the phenothiazine molecules investigated effectively reduced the temperature required to induce the formation of β-sheet-rich fibrils from α-helix-rich fibrils of PLL.

Influence of resveratrol on interactions between negatively charged DPPC/DPPG membranes and positively charged poly-l-lysine

Resveratrol (Res), a natural polyphenol present in different plants and vegetables, exhibits potential therapeutic activity with cardioprotective, antineurodegenerative, antioxidant, and antitumor action. In this study, the effect of Res on the mutual interactions between positively charged poly-l-lysine (PLL) and negatively charged dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylglycerol (DPPC/DPPG) membranes was studied using Fourier-transform infrared (FTIR) spectroscopy supported by principal component analysis (PCA). The interactions between PLL and DPPC/DPPG membranes were strongly affected by the presence of Res molecules. Depending on the Res concentration and method of its supply (through the water or lipid phase) to the studied peptide-membrane systems, the membrane-induced transition of PLL from an α-helix to an extended left-handed polyproline II helix (PPII) occurred at different temperatures, with different cooperativity, or was even completely suppressed. The influence of PLL on the conformational (trans/gauche) state of the hydrocarbon chain region of the lipid membranes and the hydration state of the polar/apolar membrane interface was also modulated by Res, depending on the membrane phase state.

Properties of Artificial Phospholipid Membranes Containing Lauryl Gallate or Cholesterol

Lauryl gallate (LG) is an antioxidant agent. However, it exhibits poor solubility in water. Its interactions with the membrane result in structure evolution thus affecting the membrane functionality. In this paper the Brewster angle microscope coupled with the Langmuir trough was applied to determine the morphology, phase behaviour, thickness and miscibility of ternary Langmuir monolayers with equal mole fractions of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC); 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and an increasing mole fraction of LG. The results were discussed as regards analogous systems where cholesterol (Chol) was the third component. Moreover, the phosphatidylcholine–lauryl gallate (PC–LG) interactions were monitored by the attenuated total reflectance Fourier transform infrared spectroscopy and time-of-flight secondary ion mass spectrometry. Besides lipid composition, the addition of LG was found to be a significant factor to modulate the model membrane properties. The LG molecules adjust themselves to the PC monolayer structure. The hydrophobic fragment is dipped into the membrane interior while the hydroxyl groups of phenolic gallate moiety associate with the polar groups of PC mainly through hydrogen bonding inducing the compacting effect. LG is found to be deeply submerged within DOPC, closer to the double bonds, and its insertion practically does not affect the DPPC/DOPC membrane fluidity. This is crucial for getting more profound insight into the role of LG in stabilizing the non-raft domains, mostly exposed to oxidation in which LG can co-localize and serve its antioxidant function.

Alpha-helix to beta-sheet transition in long-chain poly-l-lysine: Formation of alpha-helical fibrils by poly-l-lysine

The temperature-induced α-helix to β-sheet transition in long-chain poly-l-lysine (PLL), accompanied by the gauche-to-trans isomerization of CH₂ groups in the hydrocarbon side chains of Lys amino acid residues, and formation of β-sheet as well as α-helix fibrillar aggregates of PLL have been studied using Fourier-transform infrared (FT-IR) and vibrational circular dichroism (VCD) spectroscopy, and transmission electron microscopy (TEM). In a low-temperature alkaline water solution or in a methanol-rich water mixture, the secondary structure of PLL is represented by α-helical conformations with unordered and gauche-rich hydrocarbon side chains. Under these conditions, PLL molecules aggregate into α-helical fibrils. PLLs dominated by extended antiparallel β-sheet structures with highly ordered trans-rich hydrocarbon side chains are formed in a high-temperature range at alkaline pD and aggregate into fibrillar, protofibrillar, and spherical forms. Presented data support the idea that fibrillar aggregation is a varied phenomenon possible in repetitive structural elements with not only a β-sheet-rich conformation, but also an α-helical-rich conformation.

Protein aggregation and membrane lipid modifications under lactic acid stress in wild type and OPI1 deleted Saccharomyces cerevisiae strains

Background

Lactic acid is a versatile chemical platform with many different industrial applications. Yeasts have been demonstrated as attractive alternative to natural lactic acid producers since they can grow at low pH, allowing the direct purification of the product in the desired acidic form. However, when very high concentrations of organic acids are reached, the major limitation for a viable production is the toxic effect of the product. The accumulation in the cytosol of H⁺ and of the weak organic counter-anions triggers a cellular reprogramming. Here, the effects of lactic acid exposure on Saccharomycescerevisiae have been evaluated by Fourier transform infrared (FTIR) microspectroscopy. In addition to -omic techniques, describing these responses in terms of systems and networks, FTIR microspectroscopy allows a rapid acquisition of the cellular biochemical fingerprint, providing information on the major classes of macromolecules.

Results

FTIR analyses on Saccharomyces cerevisiae cells under lactic acid stress at low pH revealed some still uncharacterized traits: (1) a direct correlation between lactic acid exposure and a rearrangement in lipid hydrocarbon tails, together with a decrease in the signals of phosphatidylcholine (PC), one of the main components of cell membrane; (2) a rearrangement in the cell wall carbohydrates, including glucans and mannans (3) a significant yet transient protein aggregation, possibly responsible for the observed transient decrease of the growth rate. When repeated on the isogenic strain deleted in OPI1, encoding for a transcriptional repressor of genes involved in PC biosynthesis, FTIR analysis revealed that not only the PC levels were affected but also the cell membrane/wall composition and the accumulation of protein aggregates, resulting in higher growth rate in the presence of the stressing agent.

Conclusions

This work revealed novel effects evoked by lactic acid on cell membrane/wall composition and protein aggregation in S. cerevisiae cells. We consequently demonstrated that the targeted deletion of OPI1 resulted in improved lactic acid tolerance. Considering that stress response involves many and different cellular networks and regulations, most of which are still not implemented in modelling, these findings constitute valuable issues for interpreting cellular rewiring and for tailoring ameliorated cell factories for lactic acid production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0438-2) contains supplementary material, which is available to authorized users.

The effect of POPC acyl chains packing by aromatic amino acid methyl esters investigated by ATR-FTIR combined with QM calculations

​The packing of POPC acyl chains can be influenced by aromatic amino acid methyl esters significantly, thus the HCCH motif is packed closed to the other one of an adjacent acyl chain with enhancement by dispersion interactions.