Aromatic interactions in tryptophan-containing peptides: crystal structures of model tryptophan peptides and phenylalanine analogs

The crystal structures of the peptides, Boc-Leu-Trp-Val-OMe (1), Ac-Leu-Trp-Val-OMe (2a and 2b), Boc-Leu-Phe-Val-OMe (3), Ac-Leu-Phe-Val-OMe (4), and Boc-Ala-Aib-Leu-Trp-Val-OMe (5) have been determined by X-ray diffraction in order to explore the nature of interactions between aromatic rings, specifically the indole side chain of Trp residues. Peptide 1 adopts a type I β-turn conformation stabilized by an intramolecular 4→1 hydrogen bond. Molecules of 1 pack into helical columns stabilized by two intermolecular hydrogen bonds, Leu(1)NH...O(2)Trp(2) and IndoleNH...O(1)Leu(1). The superhelical columns further pack into the tetragonal space group P43 by means of a continuous network of indole-indole interactions. Peptide 2 crystallizes in two polymorphic forms, P21 (2a) and P212121 (2b). In both forms, the peptide backbone is extended, with antiparallel β-sheet association being observed in crystals. Extended strand conformations and antiparallel β-sheet formation are also observed in the Phe-containing analogs, Boc-Leu-Phe-Val-OMe (3) and Ac-Leu-Phe-Val-OMe (4). Peptide 5 forms a short stretch of 310-helix. Analysis of aromatic-aromatic and aromatic-amide interactions in the structures of peptides, 1, 2a, 2b are reported along with the examples of 14 Trp-containing peptides from the Cambridge Crystallographic Database. The results suggest that there is no dramatic preference for a preferred orientation of two proximal indole rings. In Trp-containing peptides specific orientations of the indole ring, with respect to the preceding and succeeding peptide units, appear to be preferred in β-turns and extended structures

The crystal structure of benzyloxycarbonyl-(α-aminoisobutyryl)-L-alanyl methyl ester

Crystals of the title compound, C20,H29,N3,O6, are monoclinic, space group P2, with a = 8-839 (3), b = f10.818 (3), c = 11.414 (2) A, β = 95.69 (2)° Z = 2; final R = 0.053. The molecular conformation is defined by the following angles (φ, ψ): Aib-1 58- 1, 36.8; Aib-2 68.3, 18.6; Ala-3 (φ) -136.2°. The molecule adopts a type 111 β -turn conformation stabilized by an intramolecular hydrogen bond between the CO of the benzyloxycarbonyl group and the NH of the alanyl residue. The hydrogen-bond parameters are N···O 2-904 Å and ∠NH···O 156.9°

Tryptophan-containing peptide helices: Interactions involving the indole side chain

Two designed peptide sequences containing Trp residues at positions i and i + 5 (Boc-Leu-Trp-Val-Ala-Aib-Leu-Trp-Val-OMe, 1) as well as i and i + 6 (Boc-Leu-Trp-Val-Aib-Ala-Aib-Leu-Trp-Val-OMe, 2) containing one and two centrally positioned Aib residues, respectively, for helix nucleation, have been shown to form stable helices in chloroform solutions. Structures derived from nuclear magnetic resonance (NMR) data reveal six and seven intramolecularly hydrogen-bonded NH groups in peptides 1 and 2, respectively. The helical conformation of octapeptide 1 has also been established in the solid state by X-ray diffraction. The crystal structure reveals an interesting packing motif in which helical columns are stabilized by side chain-backbone hydrogen bonding involving the indole Nε1H of Trp(2) as donor, and an acceptor C=O group from Leu(6) of a neighboring molecule. Helical columns also associate laterally, and strong interactions are observed between the Trp(2) and Trp(7) residues on neighboring molecules. The edge-to-face aromatic interactions between the indoles suggest a potential C-H…π interaction involving the Cζ3H of Trp(2). Concentration dependence of NMR chemical shifts provides evidence for peptide association in solution involving the Trp(2) Nε1H protons, presumably in a manner similar to that observed in the crystal

Stereochemistry of linking segments in the design of helix-helix motifs in peptides. Crystallographic comparison of a glycyl- dipropylglycyl-glycyl segment in a tripeptide and a 14-residue peptide

As part of a program to develop synthetic helix–linker–helix peptides the conformational properties of various linking segments are currently being investigated. The propensity of α,α-di-n-propylglycine (Dpg) residues to adopt backbone conformations in the extended region of the Ramachandran map, suggested by theoretical calculations and supported by experimental observations, prompted us to investigate the utility of the Gly-Dpg-Gly segment as a rigid linking motif. The crystal structure of the achiral tripeptide Boc-Gly-Dpg-Gly-OH 1 revealed a fully extended conformation (ϕ = ±178°, ψ = ±171°) at Dpg(2), with Gly(1) adopting a helical conformation (ϕ = +-72 °, ψ = +-32 °). The addition of flanking helical segments in the 14 residue peptide Boc-Val-Val-Ala-Leu-Gly-Dpg-Gly-Val-Ala-Leu-Aib-Val-Ala-Leu-OMe 2 resulted in the crystallographic characterization of a continuous helix over the entire length of the peptide. Peptide 1 crystallized in the centrosymmetric space group P21/c with a = 9.505(2) Å, b = 11.025(2) Å, c = 20.075(4) Å, β = 90.19° and Z = 4. Peptide 2 crystallized in space group P212121 with a = 10.172(1) Å, b = 17.521(4) Å, c = 46.438(12) Å and Z = 4. A comparative analysis of Gly-Dpg-Gly segments from available crystal structures indicates a high conformational variability of this segment. This analysis suggests that context and environment may be strong conformational determinants for the Gly-Dpg-Gly segment

Synthesis of Carbide Lime Waste Derived Base Catalyst (KF/CLW-Fe3O4) for Methyl Ester Production: An Optimization Study

In this paper, solid base catalyst KF/CLW-Fe3O4 was prepared from carbide lime waste, primarily calcium hydroxide with tiny amounts of carbonate and; the catalyst was used in the optimization study on the methyl ester production. The new strong base catalyst was synthesized by chemical impregnation. This catalyst was characterized by Hammett indicator analysis, Brunauer, Emmett, and Teller (BET), scanning electron microscope (SEM), X-ray diffraction (XRD) and temperature-programmed desorption (TPD) of carbon dioxide. The catalyst was further used to catalyzed the transesterification reaction to produce methyl ester. Taguchi method was used to assess the impact of catalyst at different intervals of reaction parameters, including reaction time, methanol to oil ratio, and catalyst loading. A mixed level of orthogonal array design with L9, analysis of variance (ANOVA) and signal to noise ratio were used to determine parameters that significantly impact the palm oil transesterification reaction. High methyl ester conversion was attained, and the catalyst can be easily separated and reused. KF/CLW-Fe3O4 has great potential to be used to produce methyl ester because of its high catalytic activity and environmental friendliness. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Conformation of di-n-propylglycine residues (Dpg) in peptides: Crystal structures of a type I′β-turn forming tetrapeptide and an α-helical tetradecapeptide

The crystal structures of two oligopeptides containing di-n-propylglycine (Dpg) residues, Boc-Gly-Dpg-Gly-Leu-OMe (1) and Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (2) are presented. Peptide 1 adopts a type I-turn conformation with Dpg(2)-Gly(3) at the corner positions. The 14-residue peptide 2 crystallizes with two molecules in the asymmetric unit, both of which adopt α-helical conformations stabilized by 11 successive 5 → 1 hydrogen bonds. In addition, a single 4 → 1 hydrogen bond is also observed at the N-terminus. All five Dpg residues adopt backbone torsion angles (φ,ψ) in the helical region of conformational space. Evaluation of the available structural data on Dpg peptides confirm the correlation between backbone bond angle N-Cα-C'(ζ) and the observed backbone φ,ψ, values. For ζ > 106°, helices are observed, while fully extended structures are characterized by ζ < 106°. The mean values for extended and folded conformations for the Dpg residue are 103.6° ± 1.7° and 109.9° ± 2.6°, respectively

Potency and Cytotoxicity of a Novel Gallium-Containing Mesoporous Bioactive Glass/Chitosan Composite Scaffold as Hemostatic Agents

Chitosan-based hemostats are promising candidates for immediate hemorrhage control. However, they have some disadvantages and require further improvement to achieve the desired hemostatic efficiency. Here, a series of 1% Ga2O3-containing mesoporous bioactive glass-chitosan composite scaffolds (Ga-MBG/CHT) were constructed by the lyophilization process and the effect of various concentrations of Ga-MBG (10, 30, and 50 wt %) on the hemostatic function of the CHT scaffold was assessed as compared to that of Celox Rapid gauze (CXR), a current commercially available chitosan-coated hemostatic gauze. The prepared scaffolds exhibited \u3e79% porosity and showed increased water uptake compared to that in CXR. The results of coagulation studies showed that pure CHT and composite scaffolds exhibited increased hemostatic performance with respect to CXR. Furthermore, the composite scaffold with the highest Ga-MBG content (50 wt %) had increased capability to enhancing thrombus generation, blood clotting, and platelet adhesion and aggregation than that of the scaffold made of pure CHT. The antibacterial efficacy and biocompatibility of the prepared scaffolds were also assessed by a time-killing assay and an Alamar Blue assay, respectively. Our results show that the antibacterial effect of 50% Ga-MBG/CHT was more pronounced than that of CHT and CXR. The cell viability results also demonstrated that Ga-MBG/CHT composite scaffolds had good biocompatibility, which facilitates the spreading and proliferation of human dermal fibroblast cells even with 50 wt % Ga-MBG loading. These results suggest that Ga-MBG/CHT scaffolds could be a promising hemostatic candidate for improving hemostasis in critical situations

Production and Partial Characterization of Protease from Aspergillus Flavus using Rice Mill Waste as a Substrate and its Comparision with Aspergillus Niger Protease

Abstract Proteases are one of the most important groups of industrial enzymes and occur widely in plants an

Dengue Infection and Miscarriage: A Prospective Case Control Study

Dengue is the most prevalent mosquito-borne infection with two billion of the world's population at risk and 100 million infections every year. Dengue is increasingly important due to expansion in the vector's range, increased population density in endemic areas from urbanisation, social and environment change. Miscarriage and stillbirth is associated with dengue when the illness is severe. Dengue can also be transmitted directly from the ill mother through the placenta to the fetus in later pregnancy with variable effect to the fetus. However, dengue infection is asymptomatic to mild only in almost 90% of cases and up to 20% of pregnancies miscarry. Little is known if dengue infection in early pregnancy particularly when it is asymptomatic or mild has an effect on miscarriage. Our study explored the relationship between dengue and miscarriage by looking at recent infection rates amongst women who had miscarried and those whose pregnancies were healthy in an area were dengue is common. Our study finds a positive association between recent dengue infection and miscarriage. This finding may be important in explaining some of the miscarriages in areas where dengue is common. It is also relevant to newly pregnant women from non-dengue travelling to dengue endemic areas