A Systematic Investigation and Insight into the Formation Mechanism of Bilayers of Fatty Acid/Soap Mixtures in Aqueous Solutions

Vesicles are the most common form of bilayer structures in fatty acid/soap mixtures in aqueous solutions; however, a peculiar bilayer structure called a “planar sheet” was found for the first time in the mixtures. In the past few decades, considerable research has focused on the formation theory of bilayers in fatty acid/soap mixtures. The hydrogen bond theory has been widely accepted by scientists to explain the formation of bilayers. However, except for the hydrogen bond, no other driving forces were proposed systematically. In this work, three kinds of weak interactions were investigated in detail, which could perfectly demonstrate the formation mechanism of bilayer structures in the fatty acid/soap mixtures in aqueous solutions. (i) The influence of hydrophobic interaction was detected by changing the chain length of fatty acid (C_<i>n</i>H_2<i>n</i>+1COOH), in which <i>n</i> = 10 to 18, the phase behavior was investigated, and the phase region was presented. With the help of cryogenic transmission electron microscopy (cryo-TEM) observations, deuterium nuclear magnetic resonance (²H NMR), and X-ray diffraction (XRD) measurements, the vesicles and planar sheets were determined. The chain length of C_<i>n</i>H_2<i>n</i>+1COOH has an important effect on the physical state of the hydrophobic chain, resulting in an obvious difference in the viscoelasticity of the solution samples. (ii) The existence of hydrogen bonds between fatty acids and their soaps in aqueous solutions was demonstrated by Fourier transform infrared (FT-IR) spectroscopy and molecule dynamical simulation. From the pH measurements, the pH ranges of the bilayer formation were at the p<i>K</i>_a values of fatty acids, respectively. (iii) Counterions can be embedded in the stern layer of the bilayers and screen the electrostatic repulsion between the COO^– anionic headgroups. FT-IR characterization demonstrated a bidentate bridging coordination mode between counterions and carboxylates. The conductivity measurements provided the degree of counterion binding (β = 0.854), indicating the importance of the counterions

Direct Observation of CH/CH van der Waals Interactions in Proteins by NMR

van der Waals interactions are important to protein stability and function. These interactions are usually identified empirically based on protein 3D structures. In this work, we performed a solution nuclear magnetic resonance (NMR) spectroscopy study of van der Waals interactions by detecting the through-space ^vdw<i>J</i>_CC-coupling between protein aliphatic side chain groups. Specifically, ^vdw<i>J</i>_CC-coupling values up to ∼0.5 Hz were obtained between the methyl and nearby aliphatic groups in protein GB3, providing direct experimental evidence for the van der Waals interactions. Quantum mechanical calculations suggest that the <i>J</i>-coupling is correlated with the exchange-repulsion term of van der Waals interaction. NMR detection of ^vdw<i>J</i>_CC-coupling offers a new tool to characterize such interactions in proteins

Carboxyl–Peptide Plane Stacking Is Important for Stabilization of Buried E305 of Trichoderma reesei Cel5A

Hydrogen bonds or salt bridges are usually formed to stabilize the buried ionizable residues. However, such interactions do not exist for two buried residues D271 and E305 of Trichoderma reesei Cel5A, an endoglucanase. Mutating D271 to alanine or leucine improves the enzyme thermostability quantified by the temperature <i>T</i>₅₀ due to the elimination of the desolvation penalty of the aspartic acid. However, the same mutations for E305 decrease the enzyme thermostability. Free energy calculations based on the molecular dynamics simulation predict the thermostability of D271A, D271L, and E305A (compared to WT) in line with the experimental observation but overestimate the thermostability of E305L. Quantum mechanical calculations suggest that the carboxyl–peptide plane stacking interactions occurring to E305 but not D271 are important for the carboxyl group stabilization. For the protonated carboxyl group, the interaction energy can be as much as about −4 kcal/mol for parallel stacking and about −7 kcal/mol for T-shaped stacking. For the deprotonated carboxyl group, the largest interaction energies for parallel stacking and T-shaped stacking are comparable, about −7 kcal/mol. The solvation effect generally weakens the interaction, especially for the charged system. A search of the carboxyl–peptide plane stacking in the PDB databank indicates that parallel stacking but not T-shaped stacking is quite common, and the most probable distance between the two stacking fragments is close to the value predicted by the QM calculations. This work highlights the potential role of carboxyl amide π–π stacking in the stabilization of aspartic acid and glutamic acid in proteins

Observation of α‑Helical Hydrogen-Bond Cooperativity in an Intact Protein

The presence and extent of hydrogen-bonding (H-bonding) cooperativity in proteins remains a fundamental question, which in the past has been studied extensively, mostly by infrared and fluorescence measurements on model peptides. We demonstrate that such cooperativity can be studied in an intact protein by hydrogen/deuterium exchange NMR spectroscopy. The method is based on the fact that substitution of NH by ND in a backbone amide group slightly weakens the N–H···OC hydrogen bond. Our results show that such substitution at position <i>i</i> in an α-helix impacts the ¹H and ¹⁵N chemical shifts of the amide sites of residues <i>i</i> – 3 to <i>i</i> + 3. Quantum mechanical calculations indicate that the upfield shifts of ¹H and ¹⁵N resonances at site <i>i</i>, observed upon H/D exchanges at sites <i>i</i> – 3, <i>i</i> + 1, <i>i</i> + 2, and <i>i</i> + 3, correspond to a decrease of the <i>i</i>th backbone amide electric dipole moment, which weakens its H-bonding and long-range electrostatic interactions with other backbone amides in the α-helix. These results provide new quantitative insights into the cooperativity of H-bonding in protein α-helices

Artificial Light-Harvesting System with White-Light Emission in a Bicontinuous Ionic Medium

Artificial light-harvesting systems (ALHSs), which are closely related to Förster resonance energy transfer (FRET), are among the most attractive scientific topics during the past few decades. Specifically, binary ALHSs that are composed of a fluid donor and acceptor have a simplified composition and high number density of the donor units. However, largely due to the difficulty in obtaining a fluid donor, investigation of these systems is still quite limited, especially for the ionic systems. Herein, we report a new type of binary ALHS using an ionic naphthalimide (NPI) derivative as a donor, which shows greatly improved photoluminescence for its bicontinuous liquid structure. When blending with an acceptor such as rhodamine 6G or trans-4-[4-(dimethylamino)styryl]-methylpyridinium iodide, efficient FRET was confirmed by both experimental results and molecular dynamics simulations, with an energy transfer efficiency up to ∼90%. Tunable color, including white-light emission, was achieved by tuning the acceptor/donor ratio, opening the door for a variety of applications such as light-emitting diodes and photoluminescent inks

Protein Allostery Study in Cells Using NMR Spectroscopy

Protein allostery is commonly observed in vitro. But how protein allostery behaves in cells is unknown. In this work, a protein monomer–dimer equilibrium system was built with the allosteric effect on the binding characterized using NMR spectroscopy through mutations away from the dimer interface. A chemical shift linear fitting method was developed that enabled us to accurately determine the dissociation constant. A total of 28 allosteric mutations were prepared and grouped to negative allosteric, nonallosteric, and positive allosteric modulators. ∼ 50% of mutations displayed the allosteric-state changes when moving from a buffered solution into cells. For example, there were no positive allosteric modulators in the buffered solution but eight in cells. The change in protein allostery is correlated with the interactions between the protein and the cellular environment. These interactions presumably drive the surrounding macromolecules in cells to transiently bind to the monomer and dimer mutational sites and change the free energies of the two species differently which generate new allosteric effects. These surrounding macromolecules create a new protein allostery pathway that is only present in cells

Additional file 1 of Gli1-mediated tumor cell-derived bFGF promotes tumor angiogenesis and pericyte coverage in non-small cell lung cancer

Supplementary Material 1