5-HMF is widely presented in foods and produced through the degradation of hexoses and Maillard reaction during heat treatment of foods containing reducing sugars and amino acids in an acid environment. However, controversial conclusions on the biological effects of 5-HMF have been drawn in previous studies. Therefore, the main aim of this study was to investigate the antioxidant and antiproliferative activities of 5-HMF. The 2,2'-azinobis-3-ethylbenzothiazolin-6-sulfonic acid (ABTS) assay, the 1,1-diphenyl-2-picryhydrazyl (DPPH) assay, and the hemolysis assay induced by 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) were performed to evaluate the antioxidant capacity of 5-HMF. The results showed that 5-HMF exhibited novel antioxidant activity by scavenging the ABTS and DPPH free radicals and inhibited the AAPH-induced hemolysis in a dose-dependent manner. In the hemolysis assay, the reduction of ROS and MDA contents and the increase in enzyme activities of SOD, CAT, and GPx were found in erythrocytes pretreated with 5-HMF, which demonstrated that 5-HMF could prevent the peroxidation from the source to protect the erythrocytes. The morphological changes of erythrocytes was also verified by observation using atomic force microscopy. The inhibitory effect of 5-HMF on human cancer cell proliferation was investigated by MTT assay, flow cytometric analysis, and the TUNEL and DAPI costaining assay. The results showed that 5-HMF displayed higher antiproliferative activity on human melanoma A375 cells than other cell lines. Further investigation on the action mechanisms revealed that 5-HMF could induce A375 cell apoptosis and G0/G1 cell cycle arrest. The A375 cell apoptosis that 5-HMF induced was characterized by a TUNEL and DAPI costaining assay. These findings suggest that 5-HMF could be developed as a novel natural antioxidant with potential applications in cancer chemoprevention.

The cellulose synthesizing terminal complex consisting of subunits A, B, C, and D in Acetobacter xylinum spans the outer and inner cell membranes to synthesize and extrude glucan chains, which are assembled into subelementary fibrils and further into a ribbon. We determined the structures of subunit D (AxCeSD/AxBcsD) with both N- and C-terminal His 6 tags, and in complex with cellopentaose. The structure of AxCeSD shows an exquisite cylinder shape (height: ∼65  Å , outer diameter: ∼90  Å , and inner diameter: ∼25  Å ) with a right-hand twisted dimer interface on the cylinder wall, formed by octamer as a functional unit. All N termini of the octamer are positioned inside the AxCeSD cylinder and create four passageways. The location of cellopentaoses in the complex structure suggests that four glucan chains are extruded individually through their own passageway along the dimer interface in a twisted manner. The complex structure also shows that the N-terminal loop, especially residue Lys6, seems to be important for cellulose production, as confirmed by in vivo assay using mutant cells with axcesD gene disruption and N-terminus truncation. Taking all results together, a model of the bacterial terminal complex is discussed.

Angiotensin I-converting enzyme (ACE) has an important function in blood pressure regulation. ACE-inhibitory peptides can lower blood pressure by inhibiting ACE activity. Based on the sequence of an ACE-inhibitory hexapeptide (TPTQQS) purified from yeast, enzyme kinetics experiments, isothermal titration calorimetry (ITC), and a docking simulation were performed. The hexapeptide was found to inhibit ACE in a non-competitive manner, as supported by the structural model. The hexapeptide bound to ACE via interactions of the N-terminal Thr1, Thr3, and Gln4 residues with the residues on the lid structure of ACE, and the C-terminal Ser6 attracted the zinc ion, which is vital for ACE catalysis. The displacement of the zinc ion from the active site resulted in the inhibition of ACE activity. The structural model based on the docking simulation was supported by experiments in which the peptide was modified. This study provides a new inhibitory mechanism of ACE by a peptide which broads our knowledge for drug designing against enzyme targets.

The present study was aimed at selecting an efficient binary solvent mixture for monoacylglycerol (MAG) synthesis by enzymatic glycerolysis of soybean oil. Solvent combinations of tert-butanol/isopropanol (v/v) at different ratios were studied. Of the investigated cases, tert-butanol:isopropanol at ratio 80:20 was the most suitable organic medium. The optimum conditions for MAG synthesis under the selected mixture were: water 10 wt% based on glycerol, Lipozyme TL IM 15 wt% based on oil and glycerol, weight ratio of solvent to oil 4:1, and molar ratio of glycerol to oil 3.5:1. Under these conditions with a 4-h reaction, the yield of MAG was 72.0% where the triacylglycerol (TAG) content was reduced to only 1.0% (based on acylglycerols). Fatty acid ester (FAE) formation from the solvents was very low in the final product (1.3% based on reaction mixture). The selected binary solvent mixture has good physical properties with low melting point (-26.5°C), which can avoid the risk of crystallization in practical operations.

Nanofibrils from the self-assembly of the naturally occurring saponin glycyrrhizic acid (GA) can be used to produce an oil-in-water emulsion foam with a long-term stability. Through homogenization and aeration followed by rapid cooling, stable emulsion foams can be produced from the mixtures of sunflower oil and saponin nanofibrils. At high temperatures, the GA fibrils form a multilayer assembly at the interface, creating an interfacial fibrillar network to stabilize the oil droplets and air bubbles generated during homogenization. A subsequent rapid cooling can trigger the self-assembly of free GA fibrils in the continuous phase, forming a fibrillar hydrogel and thus trapping the oil droplets and air bubbles. The viscoelastic bulk hydrogel showed a high yield stress and storage modulus, which lead to a complete arrest of the liquid drainage and a strong slowdown of the bubble coarsening in emulsion foams. The jamming of the emulsion droplets in the liquid channels as well as around the bubbles was also found to be able to enhance the foam stability. We show that such stable foam systems can be destroyed rapidly and on demand by heating because of the melting of the bulk hydrogel. The reversible gel-sol phase transition of the GA hydrogel leads to thermoresponsive emulsion foams, for which the foam stability can be switched from stable to unstable states by simply raising the temperature. The emulsion foams can be further developed to be photoresponsive by incorporating internal heat sources such as carbon black particles, which can absorb UV irradiation and convert the absorbed light energy into heat. This new class of smart responsive emulsion foams stabilized by the natural, sustainable saponin nanofibrils has potential applications in the food, pharmaceutical, and personal care industries.

The EGF-like domains in human thrombomodulin interact with and change the specificity of thrombin from a procoagulant enzyme to an anticoagulant enzyme. Recent experiments identified the minimal thrombin-binding region of thrombomodulin as the most acidic loop of the fifth EGF-like domain with a sequence of E408CPEGYILDDGFI420CTDIDE. High-resolution NMR spectroscopy was employed to characterize the interaction of a des-Ile420 thrombomodulin peptide, Cys1(409)Pro2Glu3Gly4Tyr5Ile6- Leu7Asp8Asp9Gly10Phe11Cys12Thr13Asp14Ile15Asp16Glu17(426), with its target coagulation protein, thrombin. The disulfide-bonded peptide was found to be structured only upon binding, while neither the linear nor the cyclized peptide exhibited any structural preference free in solution. The thrombin-bound structure of the cyclic thrombomodulin peptide was determined by transferred nuclear Overhauser effects (transferred NOEs) and by distance geometry and Monte Carlo calculations. The thrombin-bound cyclic peptide assumes an overall conformation similar to those observed in the free but intact EGF molecules. There is a type II beta-turn involving residues Pro2-Tyr5, followed by an optimized antiparallel beta-sheet involving residues Gly4-Asp8 and residues Phe11-Ile15. The thrombomodulin peptide provides a potential thrombin-binding surface between residues Tyr5 and Phe11, which are brought close by a chain reversal within the central beta-sheet. Comparison of the thrombin-bound structure of the EGF-like subdomain with other thrombin-peptide complexes revealed that a common thrombin-binding surface can be organized by different secondary structure elements with entirely different peptide sequences. The thrombin-bound structure of the thrombomodulin peptide may serve as a basis to understand the regulatory functions of thrombomodulin and as a guide for the design of specific inhibitors for thrombin.

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β-1,3-Glucan is one of the most abundant polysaccharides in fungi. Recognition of β-1,3-glucan occurs in both hydrolysis by glycoside hydrolases and immunological recognition. Our study provides a novel structural account of how glycoside hydrolase recognizes and hydrolyzes substrates in a triple-helical form and presents a general structural basis of β-1,3-glucan recognition.