Weak Hydrophobic Interactions Research Articles

Effect of non-covalent binding of tannins to sodium caseinate on the stability of high-internal-phase fish oil emulsions

In this study, we designed the noncovalent binding of sodium caseinate (SC) to tannic acid (TA) to stabilize high internal phase emulsions (HIPEs) used as fish oil delivery systems. Hydrogen bonding was the dominant binding force, followed by weak hydrophobic interaction and weak van der Waals forces, as demonstrated by FTIR, fluorescence spectroscopy, and molecular docking experiments, with a binding constant of 3.25 × 106, a binding site of 1.2, and a static quenching of the binding. Increasing SC:TA from SC to 2:1 decreased the particle size from 107.37 ± 10.66 to 76.07 ± 2.77 nm and the zeta potential from −6.99 ± 2.71 to −22 ± 2.42 mV. TA increased the interfacial tension of SC, decreased the surface hydrophobicity from 1.3 × 104 to 1.6 × 103 and improved the oxidation resistance of SC. The particle size of high internal phase emulsions stabilized by complexes with different mass ratios (SC:TA from 1:0 to 2:1) increased from 4.9 ± 0.02 to 12.9 μm, the potential increased from −32.37 ± 2.7 to −35.07 ± 2.58 mV, and the instability index decreased from 0.75 to 0.02. Thicker interfacial layers could be observed by laser confocal microscopy, and an increase in the storage modulus indicated a formation of a stronger gel network. SC:TA of 1:0 showed emulsion breakage after 14 d of storage at room temperature. SC:TA of 2:1 showed the lowest degree of oil-water separation after freeze-thaw treatment. Especially, the most stable high endo-phase emulsion (at SC:TA of 2:1) prepared at each mass ratio was selected for further stability exploration. The emulsion particle size increased only from 15.63 ± 0.06 to 22.27 ± 0.35 μm at salt ion concentrations of 50–200 mM and to 249.33 ± 31.79 μm at 300 mM. The instability index and storage modulus of the high endo-phase emulsions increased gradually with increasing salt ion concentrations. At different heating temperatures (55–85 °C), the instability index of the high internal phase emulsion gradually decreased and the storage modulus gradually increased. Meanwhile, at 50 °C for 15 d of accelerated oxidation, the content of hydroperoxide decreased from 53.32 ± 0.18 to 37.48 ± 0.77 nmol/g, about 29.7 %, and the thiobarbituric acid value decreased from 1.06 × 103 to 0.8 × 103, about 24.5 %, in the high endo-phase emulsions prepared by 2:1 SC:TA compared to the fish oils, and the SC-stabilized high endo-phase only emulsion broke at the sixth day of oxidation. From the above findings, it was concluded that the high internal phase emulsion prepared with SC:TA of 2:1 can be used as a good delivery system for fish oil.

Potential mechanisms and effects of ultrasound treatment combined with pre- and post-addition of κ-carrageenan on the gelling properties and rheological behavior of myofibrillar proteins under low-salt condition

This study investigated the effect of ultrasound (US) combined with pre- and post-addition of κ-carrageenan (KC) on the gelling properties, structural characteristics and rheological behavior of myofibrillar proteins (MP) under low-salt conditions. The results showed that US combined with either pre- or post-addition of KC rendered higher gel strength and water holding capacity (WHC) of MP gels than those treated with US alone and added with KC alone (P < 0.05). US combined with pre-addition of KC facilitated the binding between MP and KC, which enhanced the gel strength and WHC of the mixed MP gels and significantly improved the rheological behavior of MP. This was also confirmed by the highest surface hydrophobicity, disulfide bonds and β-sheet content of the MP gels with US combined with pre-addition of KC. Moreover, microstructural results reflected a denser structure for the pre-addition of KC in combination with US. However, US combined with post-addition of KC resulted in limited MP unfolding and relatively weak hydrophobic interactions in the composite gels, which were less effective in improving the gel properties of the MP gels. This study provides potential strategies for enhancing the gelling properties of low-salt meat products via application of US and KC.

Effect of Bacterial Amyloid Protein Phenol-Soluble Modulin Alpha 3 on the Aggregation of Amyloid Beta Protein Associated with Alzheimer's Disease.

Since the proposal of the brainstem axis theory, increasing research attention has been paid to the interactions between bacterial amyloids produced by intestinal flora and the amyloid β-protein (Aβ) related to Alzheimer's disease (AD), and it has been considered as the possible cause of AD. Therefore, phenol-soluble modulin (PSM) α3, the most virulent protein secreted by Staphylococcus aureus, has attracted much attention. In this work, the effect of PSMα3 with a unique cross-α fibril architecture on the aggregation of pathogenic Aβ40 of AD was studied by extensive biophysical characterizations. The results proposed that the PSMα3 monomer inhibited the aggregation of Aβ40 in a concentration-dependent manner and changed the aggregation pathway to form granular aggregates. However, PSMα3 oligomers promoted the generation of the β-sheet structure, thus shortening the lag phase of Aβ40 aggregation. Moreover, the higher the cross-α content of PSMα3, the stronger the effect of the promotion, indicating that the cross-α structure of PSMα3 plays a crucial role in the aggregation of Aβ40. Further molecular dynamics (MD) simulations have shown that the Met1-Gly20 region in the PSMα3 monomer can be combined with the Asp1-Ala2 and His13-Val36 regions in the Aβ40 monomer by hydrophobic and electrostatic interactions, which prevents the conformational conversion of Aβ40 from the α-helix to β-sheet structure. By contrast, PSMα3 oligomers mainly combined with the central hydrophobic core (CHC) and the C-terminal region of the Aβ40 monomer by weak H-bonding and hydrophobic interactions, which could not inhibit the transition to the β-sheet structure in the aggregation pathway. Thus, the research has unraveled molecular interactions between Aβ40 and PSMα3 of different structures and provided a deeper understanding of the complex interactions between bacterial amyloids and AD-related pathogenic Aβ.

Potential of milk fat globule membrane's phospholipids and anhydrous milk fat based nanostructured lipid carriers for enhanced bioaccessibility of vitamin D3

Novel nanostructured lipid carriers (NLCs) were engineered using anhydrous milk fat (AMF) as vitamin-D3 (VD3) carrier and milk fat globule membrane (MFGM) phospholipids (PLs) as surfactants. Significantly higher encapsulation efficiency of VD3 was obtained (96 ± 2.5%) in AMF-MFGM-PLs NLCs. Void and VD3 loaded NLCs had diameters of 150 ± 0.2 nm and 167 ± 2 nm and ζ-potentials of −15.5 ± 1.6 mV and −15.9 ± 0.3 mV, respectively. NLCs had spherical morphology; VD3 was distributed in the lipid core of NLCs via weak electrostatic or hydrophobic interactions. Physical stability in terms of particle size and homogeneity of particles was attained for a three-week storage period. Biphasic in-vitro controlled release kinetics was observed, i.e., burst release followed by sustained release up to 21 days. VD3 exhibited effective chemical stability (48.3 ± 3.4%) and significantly higher bioaccessibility (88 ± 2.6%) after complete simulated in-vitro digestion. VD3 loaded NLCs are promising natural vehicles for the effective delivery of less-bioaccessible vitamins to overcome micronutrient deficiency.

Dispersal of PRC1 condensates disrupts polycomb chromatin domains and loops.

Polycomb repressive complex 1 (PRC1) strongly influences 3D genome organization, mediating local chromatin compaction and clustering of target loci. Several PRC1 subunits have the capacity to form biomolecular condensates through liquid-liquid phase separation in vitro and when tagged and over-expressed in cells. Here, we use 1,6-hexanediol, which can disrupt liquid-like condensates, to examine the role of endogenous PRC1 biomolecular condensates on local and chromosome-wide clustering of PRC1-bound loci. Using imaging and chromatin immunoprecipitation, we show that PRC1-mediated chromatin compaction and clustering of targeted genomic loci-at different length scales-can be reversibly disrupted by the addition and subsequent removal of 1,6-hexanediol to mouse embryonic stem cells. Decompaction and dispersal of polycomb domains and clusters cannot be solely attributable to reduced PRC1 occupancy detected by chromatin immunoprecipitation following 1,6-hexanediol treatment as the addition of 2,5-hexanediol has similar effects on binding despite this alcohol not perturbing PRC1-mediated 3D clustering, at least at the sub-megabase and megabase scales. These results suggest that weak hydrophobic interactions between PRC1 molecules may have a role in polycomb-mediated genome organization.

Impact of 1,6-hexanediol on Schizosaccharomyces pombe genome stability.

Phase separation is a major mechanism of macromolecular condensation within cells. A frequently chosen tool for global disruption of phase separation via weak hydrophobic interactions is treatment with 1,6-hexanediol. This study evaluates the cytotoxic and genotoxic effects of treating live fission yeast with 1,6-hexanediol. We find that 1,6-hexanediol causes a drastic decrease in cell survival and growth rate. We also see a reduction in HP1 protein foci and increase in DNA damage foci. However, there is no evidence for increased genomic instability in two classically phase-separated domains, the heterochromatic pericentromere and the nucleolar rDNA repeats. This study reveals that 1,6-hexanediol is a blunt tool for phase separation inhibition and its secondary effects must be taken into consideration during its in vivo use.

Evaluation of Kinetic Performance of Reversed-Phase Columns for Protein Separations by Gradient Kinetic Plots

The increasing importance of protein biopharmaceuticals has triggered the development of new, highly efficient stationary phases for reversed-phase liquid chromatography (LC) of proteins. They typically have C4 ligands or phenyl surfaces for weak hydrophobic interactions and are based on various morphologies, such as silica monolith, sub-2-µm fully porous particles (FPPs), or superficially porous particles (SPPs). Selection of the best column based on physical parameters provided by vendors may sometimes be unequivocal. Simple performance evaluation tools, such as the gradient kinetic plot methodology reported by Desmet and co-workers, can help to shed light on this issue and allow for a more differentiated view on column performance. This article compares the performance of wide-pore silica monolithic, sub-2-µm FPP, and SPP columns. It also addresses the question of whether 1000 Å or 400 Å SPP columns are more suitable for reversed-phase LC-type protein separations and presents a kinetic performance comparison of a number of wide-pore core–shell particle columns.

Using Different Surface Energy Models to Assess the Interactions between Antiviral Coating Films and phi6 Model Virus

High molecular weight chitosan (HMWCh), quaternised cellulose nanofibrils (qCNF), and their mixture showed antiviral potential in liquid phase, while this effect decreased when applied to facial masks, as studied in our recent work. To gain more insight into material antiviral activity, spin-coated thin films were prepared from each suspension (HMWCh, qCNF) and their mixture with a 1:1 ratio. To understand their mechanism of action, the interactions between these model films with various polar and nonpolar liquids and bacteriophage phi6 (in liquid phase) as a viral surrogate were studied. Surface free energy (SFE) estimates were used as a tool to evaluate the potential adhesion of different polar liquid phases to these films by contact angle measurements (CA) using the sessile drop method. The Fowkes, Owens-Wendt-Rabel-Kealble (OWRK), Wu, and van Oss-Chaudhury-Good (vOGC) mathematical models were used to estimate surface free energy and its polar and dispersive contributions, as well as the Lewis acid and Lewis base contributions. In addition, the surface tension SFT of liquids was also determined. The adhesion and cohesion forces in wetting processes were also observed. The estimated SFE of spin-coated films varied between mathematical models (26-31 mJ/m2) depending on the polarity of the solvents tested, but the correlation between models clearly indicated a significant dominance of the dispersion components that hinder wettability. The poor wettability was also supported by the fact that the cohesive forces in the liquid phase were stronger than the adhesion to the contact surface. In addition, the dispersive (hydrophobic) component dominated in the phi6 dispersion, and since this was also the case in the spin-coated films, it can be assumed that weak physical van der Waals forces (dispersion forces) and hydrophobic interactions occurred between phi6 and the polysaccharide films, resulting in the virus not being in sufficient contact with the tested material during antiviral testing of the material to be inactivated by the active coatings of the polysaccharides used. Regarding the contact killing mechanism, this is a disadvantage that can be overcome by changing the previous material surface (activation). In this way, HMWCh, qCNF, and their mixture can attach to the material surface with better adhesion, thickness, and different shape and orientation, resulting in a more dominant polar fraction of SFE and thus enabling the interactions within the polar part of phi6 dispersion.

Inhibitory mechanism of n-MTAB AuNPs for α-synuclein aggregation.

The aggregation of alpha-synuclein (α-syn) is closely related to the pathogenesis anddysfunction of Parkinson's disease. To investigate the potential of nanoparticlemediatedtherapy, the interactive mechanism between α-syn and n-myristyltrimethylammonium bromide (MTAB)Gold nanoparticles (AuNPs) with different diameters was explored by molecular dynamics simulations. The results indicated that there was a directional interaction between α-syn and n-MTABAuNPs, in which the driving force for the binding of the C-terminus in α-syn came from electrostatic interactions andthe nonamyloid β component (NAC) domain exhibited weak hydrophobic interactions as well as electrostaticinteraction, thereby preventing α-syn aggregation. Energy statistics and analysis showed that for 5-MTAB AuNPs,acidic amino acids such as Glu and Asp played a very important role. This studynot only demonstrated a theoretical foundation for the behavior of biomolecules directionally adsorbed on thesurface of biofunctional nanoparticles but also indicated that 5-MTAB AuNPs may be a potential inhibitor againstα-syn protein aggregation.

Creatinase: Using Increased Entropy to Improve the Activity and Thermostability.

Improving protein thermostability in mutagenesis-based enzyme engineering was often achieved by enhancing interresidue interactions via mutation to increase the enthalpy penalty of unfolding. However, this approach may trade off the functional activity due to the loss of structural flexibility of the biomolecule. Here, by performing X-ray crystallography, enzymatic kinetic experiments, neutron scattering, and thermodynamical measurements, we compared the structures, catalytic behaviors, dynamics, and thermostability between a wild-type creatinase and its four-point mutant. We found that the mutant is an entropy-driven thermostable protein with higher structural flexibility, i.e., higher conformational entropy, in the folded state compared to the wild type. The increased conformational entropy of the mutant in the folded state can reduce the entropy gain during unfolding and thus renders it greater thermostability. Moreover, the increased structural flexibility, particularly around the catalytic site, can broaden the mutant's working temperature range and considerably improve its activity at ambient conditions, which is crucial for its application in diagnosing kidney diseases. Complementary all-atom molecular dynamics simulations indicated that the four mutations replaced several of the strong interresidue interactions (electrostatic interactions and hydrogen bonds) with weak hydrophobic interactions. These substitutions not only release the structural flexibility to promote the thermostability and enzymatic activity of the protein but they also preserve the protein structure from collapsing. Our findings may pave a route for the entropy-driven strategy to design proteins with high thermostability and activity.

Potential of pectin-chitosan based composite films embedded with quercetin-loaded nanofillers to control meat associated spoilage bacteria

Increasing consumer demands for healthy, minimally processed, contamination-free food with extended shelf life have exerted pressure on the food industry to search for more effective and biodegradable packaging materials against spoilage agents. Pectin-chitosan based nanocomposite films were developed and evaluated for the impacts of antimicrobial-loaded nanofillers [(quercetin-loaded nano-liposomes (QNLs)] on the physico-mechanical, thermal, and antibacterial properties against meat-associated spoilage pathogens. QNLs were observed with an average size of 191 ± 7 nm by dynamic light scattering with a negative zeta-potential value of −37 ± 5.7 mV. Scanning electron microscopy revealed round and smooth surface morphology of QNLs. FTIR spectroscopic analyses confirmed the encapsulation of quercetin in liposomes via weak electrostatic or hydrophobic interactions. The addition of nanofillers in composite films increased the tensile strength (9.74 ± 0.26 MPa) and Young's modulus (24.17 ± 0.64 MPa) of the nano-active films as compared to active films (2.49 ± 0.02 MPa and 5.04 ± 0.04 MPa), respectively. Similarly, opacity (3.10 ± 0.04) and moisture content (31.03% ± 1.81%) values of nano-active films were lesser as compared to non-active films (5.35% ± 0.07% and 84.24% ± 0.45% respectively) owing to the hydrophobic nature of QNLs. Thermal analyses performed by TGA and DSC confirmed the thermal stability of nano-active films. Nano-active films exhibited excellent antimicrobial potential (spot-on-lawn and quantitative food application assays) against multidrug-resistant meat pathogens including Escherichia coli, Listeria monocytogenes and Salmonella enterica. Hence, pectin-chitosan based nano-active films have promising applications for the preservation of meat products from spoilage bacteria.

The effect of high‐pressure homogenization on rabbit myofibrillar proteins in dilute sodium chloride solutions: weak ionic shielding promotes the depolymerisation

SummaryThe study attempts to determine the effect of ionic strength on the structure and solubility of rabbit myofibrillar proteins (MPs) and improves MPs dissolution in low salt medium. There was a significant effect of ionic strength on the structure and dissolution characteristics of MPs in low salt medium range (0–200 mM NaCl), increased ionic strength led to MPs aggregation and reduced solubility (P &lt; 0.05), while decreased ionic strength weakened charge shielding effect, resulted in stronger electrostatic repulsion and weaker hydrophobic interaction between molecules, thus promoting MPs structural swell and separation between filaments. The modification effect of HPH on the MPs also depended on the ionic strength. Upon HPH, due to the difference in charge shielding effect and hydrophobic interactions, there was a progressive improvement in MPs solubility (from 23.51% to 85.25%) and dispersion stability at 0 mM salt medium (I = 0.0217) while limited increase in solubility at medium higher than 13 mM (from 4.39% to 7.20% at 20 mM). Decreasing ionic strength promoted the depolymerisation of HPH on MPs, inhibited the myosin assembly into filaments after HPH. The modification of ionic strength on the surface charge and hydrophobicity of MPs were further amplified, also contributed to the improved solubility and dispersion stability.

Improvement of the encapsulation capacity and emulsifying properties of soy protein isolate through controlled enzymatic hydrolysis

Self-assembling nanoparticle made from soy protein hydrolysates has proved to be a promising delivery system due to its excellent biocompatibility and synthetic feasibility. In this study, the critical parameters that control the SPI hydrolysate structure and its encapsulation capacity have been assessed. Three different enzymes, including Flavorzyme, Neutrase and Alcalase, were selected to hydrolyze soy protein isolate (SPI), and a solvent evaporation method was used to fabricate β-carotene loaded nanoparticles. Microstructure observation, SDS-PAGE, surface hydrophobicity, and endogenous fluorescence analysis were carried out to examine the key structural factors influencing encapsulation efficiency of SPI hydrolysates nanoparticles (SPIHs). It was found moderate exposure of hydrophobic amino acids inside the 7 S globulin via Flavorzyme controlled hydrolysis can increase the surface hydrophobicity of SPIH, therefore improving its emulsifying properties, while excessive hydrolysis of 7 S by Alcalase would cause weak hydrophobic interactions between the hydrophobic amino acids, which restricted the binding site with β-carotene. Above results provide a foundation for fabricating nanoparticles encapsulating lipophilic compounds with high encapsulation rate from SPI hydrolysates (SPIH).

How does Poly(ethylene glycol) with varied chain length affect the thermo-responsive behavior of methyl cellulose in aqueous solutions?

In this study, by using a set of narrowly distributed polyethylene glycol (PEG) samples with varied average molar mass (PEGn, 9 <n < 454), we have systematically studied how PEG molar mass and solution concentration influence the thermal response behavior of methyl cellulose (MC) aqueous solutions (Mw = 4.3 × 105 g/mol, <Rg> = 71 nm) by a combination of isothermal titration calorimetry (ITC), rheometer, UV–vis spectroscopy, laser light scattering (LLS) and atomic force microscopy (AFM). At room temperature, ITC result clarifies the existence of extremely weak hydrophobic interactions between MC and PEG chains. In addition, for MC/PEG mixed solution with shorter PEGs (PEG22 and PEG90), experimentally measured zero-shear viscosity (ηexp) is confirmed to be 5–10% higher than the theoretical values (ηcalc), further supporting the interchain association. Whereas for MC/PEG454, insoluble aggregates are formed, which results in ηexp < ηcalc. Further, dynamic laser scattering (DLS) results further reveal how the percentage of peak area of aggregates depends on the chain length of PEG. During the heating process from T = 20 to 70 °C, a combination of UV, LLS and AFM results clearly illustrates that the shorter PEG chains can effectively stabilize the formed MC fibers and prevent the fiber extension; whereas for longer PEG chains, they can not only promote the nucleation process, but also destabilize the formed fibers and promote the fiber extension. Our result unambiguously reveals the macromolecular effect of PEGs on the thermal response behavior of MC in solutions.

Hydrophobic Cluster Formation in Aqueous Ethanol Solutions Probed by Soft X-ray Absorption Spectroscopy.

Hydrophobic cluster structures in aqueous ethanol solutions at different concentrations have been investigated by soft X-ray absorption spectroscopy (XAS). In the O K-edge XAS, we have found that hydrogen bond structures among water molecules are enhanced in the middle-concentration region by the hydrophobic interaction of the ethyl groups in ethanol. In the C K-edge XAS, the lower energy features arise from a transition from the terminal methyl C 1s electron to an unoccupied orbital of 3s Rydberg character, which is sensitive to the nearest-neighbor intermolecular interactions. From the comparison of C K-edge XAS with the inner-shell calculations, we have found that ethanol clusters are easily formed in the middle-concentration region due to the hydrophobic interaction of the ethyl group in ethanol, resulting in the enhancement of the hydrogen bond structures among water molecules. This behavior is different from aqueous methanol solutions, where the methanol-water mixed clusters are more predominant in the middle-concentration region due to the relatively weak hydrophobic interactions of the methyl group in methanol.

Magnetically responsive hydrophobic pockets for on–off drug release

The vast majority of drugs available on the market are hydrophobic compounds. As a result, their poor water solubility can critically compromise the overall absorption of these drugs by patients. Although numerous different strategies have been developed to improve their bioavailability, the controlled delivery of these drugs is still a challenge. In this sense, stimuli-responsive hydrogels could be a solution to improve administration and stable release. However, the strategies required to render hydrogels hydrophobic mostly rely on weak hydrophobic interactions, which can lead to disassembly of the system and undesired burst discharge. Accordingly, the on-demand release of poorly water-soluble drugs is still a major milestone in this field. To circumvent these setbacks, we present for the first time a hydrophobic, magnetically responsive hydrogel based on the diaminotriazine (DAT) skeleton. The versatility of DATs in terms of H-bond formation and metal complexation simultaneously endows the hydrogel with hydrophobicity and magnetic responsiveness, thus allowing both the efficient loading and on–off release of a model hydrophobic drug as well as of a hydrophobic bioactive substance. Theoretical calculations further suggested stable formation of DAT aggregates that operate as efficient hydrophobic cavities or ‘pockets’ for these compounds. Moreover, these materials were found to be suitable for enhancing the viability and growth of cell lines often used as in vitro models of neuronal function and differentiation. The present magnetic hydrogels hold interesting potential for tissue engineering as biocompatible scaffolds for the on-demand release of hydrophobic compounds, which remains the focus of current research efforts.

Rapid polymerization of polyhedral oligomeric siloxane-based zwitterionic sulfoalkylbetaine monolithic column in ionic liquid for hydrophilic interaction capillary electrochromatography

A novel polyhedral oligomeric siloxane (POSS)-based zwitterionic monolithic capillary column was prepared via one-pot polymerization in ionic liquid porogen, using N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)ammonium betaine (DMMSA) and methacrylic ethyl trimethylammonium chloride (META) as binary functional monomers, and methacryl substituted POSS as cross-linker. The pore structure, permeability and homogeneity were well tuned by optimizing the polymerization conditions. The resultant monolith was characterized by scanning electron microscopy, nitrogen adsorption/desorption isotherm and Fourier transform infrared spectroscopy. The incorporation of zwitterionic ligand (DMMSA), quaternary amine group (META) and rigid POSS skeleton endows the hybrid organic-silica monolith with high hydrophilicity, electrostatic interaction and good mechanical stability, as well as a tunable electroosmotic flow over wide pH range. A close investigation of capillary electrochromatographic separations of different types of polar compounds such as bases, nucleosides and benzoic acids on such stationary phase exhibited a retention independent column efficiency up to 118,000 plates/m (thiourea), as well as a mixed-mode hydrophilic interaction chromatography (HILIC) retention mechanism including weak electrostatic interaction, hydrophobic interaction and anion exchange.

Changes in Hydrophobic Interactions among Gluten Proteins during Dough Formation

In this study, changes in hydrophobic interactions among gluten proteins were analyzed during dough mixing. Size-exclusion high-performance chromatography and two-dimensional fluorescence difference gel electrophoresis were performed on proteins extracted with 1-propanol by weakening the hydrophobic interaction. The amount of proteins extracted with 30% 1-propanol increased from the start of mixing to peak consistency, suggesting that the hydrophobic interactions among the strongly aggregated proteins weakened and resulted in disaggregation. The amount of proteins extracted with 10% 1-propanol decreased during hydration, indicating that these proteins aggregated through relatively weak hydrophobic interactions. The proteins that extractability decreased were mainly low molecular weight glutenin, α-gliadin, and γ-gliadin. The amount of monomeric proteins extracted with 30% 1-propanol decreased after peak consistency. The decreased protein was mainly ω-gliadin, indicating that ω-gliadin aggregated with other proteins through hydrophobic interactions. A front-face fluorescence analysis was performed on the dough with the addition of 8-anilino-1-naphthalenesulfonic acid or thioflavin T. The fluorescence intensity increased as a result of exposure to the hydrophobic groups of the gluten proteins and the formation of protein aggregates during dough mixing. These results indicate the importance of hydrophobic interactions in dough formation.

Weak Interplay between Hydrophobic Part of Water-soluble Polymers and Serum Protein

Glucosamine-bearing poly(styrene-co-maleic acid) (SMA-G) with the molecular weight of 1.8 × 104 is water soluble. We found that there is a weak hydrophobic interaction between water soluble serum protein and SMA-G, and they can form a complex through an endothermic process. This entropy-driven interplay may play an important role in drug delivery through SMA-G.

Crystal structure of a photosynthetic LH1-RC in complex with its electron donor HiPIP

Photosynthetic electron transfers occur through multiple components ranging from small soluble proteins to large integral membrane protein complexes. Co-crystallization of a bacterial photosynthetic electron transfer complex that employs weak hydrophobic interactions was achieved by using high-molar-ratio mixtures of a soluble donor protein (high-potential iron-sulfur protein, HiPIP) with a membrane-embedded acceptor protein (reaction center, RC) at acidic pH. The structure of the co-complex offers a snapshot of a transient bioenergetic event and revealed a molecular basis for thermodynamically unfavorable interprotein electron tunneling. HiPIP binds to the surface of the tetraheme cytochrome subunit in the light-harvesting (LH1) complex-associated RC in close proximity to the low-potential heme-1 group. The binding interface between the two proteins is primarily formed by uncharged residues and is characterized by hydrophobic features. This co-crystal structure provides a model for the detailed study of long-range trans-protein electron tunneling pathways in biological systems.