Monitoring the Interactions of a Ternary Complex Using NMR Spectroscopy: The Case of Sugars, Polyphenols, and Proteins

Gaining insight into intermolecular interactions between multiple species is possible at an atomic level by looking at different parameters using different NMR techniques. In the specific case of the astringency sensation, in which at least three molecular species are involved, different NMR techniques combined with dynamic light scattering and molecular modeling contribute to decipher the role of each component in the interaction mode and to assess the thermodynamic parameters governing this complex interaction. The binding process between a saliva peptide, a polyphenol, and polysaccharides was monitored by following ¹H chemical shift variations, changes in NMR peak areas, and size of the formed complex. These NMR experiments deliver a complete picture of the association pathway, assessed by dynamic light scattering and molecular dynamics simulations: all of the data collected converge toward a comprehensive mode of interaction in which sugars indirectly play a role in astringency by sequestering part of the polyphenols, reducing their effective concentration to bind saliva proteins

Sequestering Hydrated Fluoride in a Three-Dimensional Non-Interpenetrated Octahedral Coordination Polymer via a Single-Crystal-to-Single-Crystal Fashion

A three-dimensional non-interpenetrated octahedral channel type coordination polymer [{Cu­(<b>L1</b>)₂(Cl)}·Cl·(H₂O)₄]_∝ (<b>1</b>) (<b>L</b><b>1</b> =<i> N</i>,<i>N′-</i>bis-(3-pyridyl)­terephthalamide) possessing an inclusion of chloride water cluster [Cl­(H₂O)₄]⁻ exhibits sequestering of partially hydrated fluoride [F­(H₂O)₄]⁻ via a single-crystal-to-single-crystal fashion as evident from single crystal X-ray diffraction and solid state ¹⁹F NMR

Aminosilane/Oleic Acid Vesicles as Model Membranes of Protocells

Oleic acid vesicles represent good models of membrane protocells that could have existed in prebiotic times. Here, we report the formation, growth polymorphism, and dynamics of oleic acid spherical vesicles (1–10 μm), stable elongated vesicles (>50 μm length; 1–3 μm diameter), and chains of vesicles (pearl necklaces, >50 μm length; 1–3 μm diameter) in the presence of aminopropyl triethoxysilane and guanidine hydrochloride. These vesicles exhibit a remarkable behavior with temperature: spherical vesicles only are observed when keeping the sample at 4 °C for 2 h, and self-aggregated spherical vesicles occur upon freezing/unfreezing (−20/20 °C) samples. Rather homogeneous elongated vesicles are reformed upon heating samples at 80 °C. The phenomenon is reversible through cycles of freezing/heating or cooling/heating of the same sample. Deuterium NMR evidences a chain packing rigidity similar to that of phospholipid bilayers in cellular biomembranes. We expect these bilayered vesicles to be surrounded by a layer of aminosilane oligomers, offering a variant model for membrane protocells

Sequestering Hydrated Fluoride in a Three-Dimensional Non-Interpenetrated Octahedral Coordination Polymer via a Single-Crystal-to-Single-Crystal Fashion

A three-dimensional non-interpenetrated octahedral channel type coordination polymer [{Cu­(<b>L1</b>)₂(Cl)}·Cl·(H₂O)₄]_∝ (<b>1</b>) (<b>L</b><b>1</b> =<i> N</i>,<i>N′-</i>bis-(3-pyridyl)­terephthalamide) possessing an inclusion of chloride water cluster [Cl­(H₂O)₄]⁻ exhibits sequestering of partially hydrated fluoride [F­(H₂O)₄]⁻ via a single-crystal-to-single-crystal fashion as evident from single crystal X-ray diffraction and solid state ¹⁹F NMR

The Colloidal State of Tannins Impacts the Nature of Their Interaction with Proteins: The Case of Salivary Proline-Rich Protein/Procyanidins Binding

While the definition of tannins has been historically associated with its propensity to bind proteins in a nonspecific way, it is now admitted that specific interaction also occurs. The case of the astringency perception is a good example to illustrate this phenomenon: astringency is commonly described as a tactile sensation induced by the precipitation of a complex composed of proline-rich proteins present in the human saliva and tannins present in beverages such as tea or red wines. In the present work, the interactions between a human saliva protein segment and three different procyanidins (B1, B3, and C2) were investigated at the atomic level by NMR and molecular dynamics. The data provided evidence for (i) an increase in affinity compared to shortest human saliva peptides, which is accounted for by protein “wraping around” the tannin, (ii) a specificity in the interaction below tannin critical micelle concentration (CMC) of ca. 10 mM, with an affinity scale such that C2 > B1 > B3, and (iii) a nonspecific binding above tannin CMC that conducts irremediably to the precipitation of the tannins/protein complex. Such physicochemical findings describe in accurate terms saliva protein–tannin interactions and provide support for a more subtle description by oenologists of wine astringency perception in the mouth

Red Wine Tannins Fluidify and Precipitate Lipid Liposomes and Bicelles. A Role for Lipids in Wine Tasting?

Sensory properties of red wine tannins are bound to complex interactions between saliva proteins, membranes taste receptors of the oral cavity, and lipids or proteins from the human diet. Whereas astringency has been widely studied in terms of tannin–saliva protein colloidal complexes, little is known about interactions between tannins and lipids and their implications in the taste of wine. This study deals with tannin–lipid interactions, by mimicking both oral cavity membranes by micrometric size liposomes and lipid droplets in food by nanometric isotropic bicelles. Deuterium and phosphorus solid-state NMR demonstrated the membrane hydrophobic core disordering promoted by catechin (C), epicatechin (EC), and epigallocatechin gallate (EGCG), the latter appearing more efficient. C and EGCG destabilize isotropic bicelles and convert them into an inverted hexagonal phase. Tannins are shown to be located at the membrane interface and stabilize the lamellar phases. These newly found properties point out the importance of lipids in the complex interactions that happen in the mouth during organoleptic feeling when ingesting tannins

Poly-phosphoinositides in 0.1% nuclei and whole sperm are enriched in the acrosomal and centriolar fossae.

<p><i>L. pictus</i> 0.1% nuclei (left) and whole live sperm (right) were incubated with the Texas Red labelled MARCKS peptide and visualised by fluorescence microscopy. The punctate staining of the acrosomal and centriolar fossae is typical of the majority of nuclei observed in experiments on two independent sperm and 0.1% nuclei preparations.</p

Nuclear envelope remnant phospholipid species are mainly polyunsaturated and arachidonyl.

<p>PtdCho, PtdEth and PtdIns species extracted from <i>L. pictus</i> 0.1% nuclei were characterized using the precursor ion scans of +184m/z, −196m/z and −241m/z respectively. Both alkyl-acyl (denoted by ‘a’) and diacyl species were mostly arachidonyl on their sn₂ positions. Lipid species are listed by descending order of abundance.</p

Nuclear envelope remnants are enriched in polyphosphoinositides.

<p>Lipid analysis of nuclear envelope remnants. (A) Lipids extracted from <i>L. pictus</i> demembranated sperm cells were separated by HPLC on a normal phase column and characterized by ESI-MS/MS using the precursor ion scans of sphingomyelin (SM), phosphatidylglycerol (PtdGly), phosphatidylethanolamine (PtdEth), phosphatidic acid (PtdAc), phosphatidylserine (PtdSer), phosphatidylcholine (PtdCho), phosphatidylinositol (PtdIns) or using the multiple ion scans of phosphatidylinositolphosphate (PtdInsP), phosphatidylinositolbisphosphate (PtdInsP₂) and phosphatidylinositoltrisphosphate (PtdInsP₃). Phospholipids were quantified using 12∶0/12∶0 (SM, PtdGly, PtdEth, PtdAc, PtdSer and PtdCho) or 16∶0/16∶0 (PtdIns, PtdInsP, PtdInsP₂ and PtdInsP₃) internal standards. Data expressed as mean±SEM (n = 3). (B) Alkyl-acyl versus diacyl phosphoinositides species distribution in nuclear envelope remnants. Mole percentages of diacyl species (green) and alkyl-acyl species (blue) were quantified from the multiple ion scans for each phosphoinositide class: PtdInsP, PtdInsP₂ and PtdInsP₃. 38% of PtdInsP, 15% of PtdInsP₂ and 49% of PtdInsP₃ are diacyl species. The PtdInsP₂ is predominantly alkyl-acyl phosphoinositide. Data expressed as mean±SEM (n = 3).</p

Nuclear envelope remnants contain two membranes that line the acrosomal and centriolar fossae.

<p>(A) <i>P. lividus</i> sperm cells were fixed in the presence of 1% (w/v) tannic acid. The plasma membrane (PM) and the mitochondrial membranes (MM) are shown. AV: acrosomal vesicle, N: nucleus, F: flagellum. The nuclear envelope is tightly apposed to the chromatin but cup-like structures with nuclear envelope remnants can be seen at the poles (arrows). (B and C) <i>S. purpuratus</i> 0.1% nuclei were incubated in egg cytoplasm supplemented with ATP-GS and fixed in the presence of 1% (w/v) tannic acid. Electron dense structures (arrows) are shown in the centriolar (B) and acrosomal fossae (C). The two bilayers appear to have variable amounts of electron dense material between them. (D) Cryosections of <i>S. purpuratus</i> 0.1% nuclei prefixed in 4% (v/v) formaldehyde for 3h on ice show two membranes in the centriolar fossa (arrows). (E) <i>S. purpuratus</i> 0.1% nuclei were incubated in egg cytoplasm in the presence of an ATP-generating system, fixed in 2.5% (v/v) glutaraldehyde in the presence of 1% (w/v) tannic acid and viewed by TEM. The glancing cross section of the centriolar fossa shows the nuclear envelope remnants and an egg membrane vesicle (arrow) associated with the nuclear envelope remnants. Bars are 500nm (A), 400nm (B) and 200nm (C, D and E). The data are representative of nuclei observed in at least 3 experiments on independent nuclei preparations.</p