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The binding interaction between-epigallocatechin-3-gallate (EGCG) and bovine β-lactoglobulin (βLG) was thoroughly studied by fluorescence, circular dichroism (CD) and protein-ligand docking. Fluorescence data revealed that the fluorescence quenching of βLG by EGCG was the result of the formation of a complex of βLG-EGCG. The binding constants and thermodynamic parameters at two different temperatures and the binding force were determined. The binding interaction between EGCG and βLG was mainly hydrophobic and the complex was stabilised by hydrogen bonding. The results suggested that βLG in complex with EGCG changes its native conformation. Furthermore, preheat treatment (90 °C, 120 °C) and emulsifier (sucrose fatty acid ester) all boosted the binding constants ( Ka) and the binding site values ( n) of the βLG-EGCG complex. This study provided important insight into the mechanism of binding interactions of green tea flavonoids with milk protein. [ABSTRACT FROM AUTHOR]

Chorismate mutase catalyzes the conversion of chorismate to prephenate in the biosynthesis of the aromatic amino acids tyrosine and phenylalanine in bacteria, fungi and plants. Here, the crystallization of the unusual secreted chorismate mutase from Mycobacterium tuberculosis (encoded by Rv1885c), a 37.2 kDa dimeric protein belonging to the AroQγ subclass of mutases, is reported. Crystal optimization was non-trivial and is discussed in detail. To obtain crystals of sufficient quality, it was critical to initiate crystallization at higher precipitant concentration and then transfer the drops to lower precipitant concentrations within 5–15 min, in an adaptation of a previously described technique [Saridakis & Chayen (2000), Protein Sci. 9, 755–757]. As a result of the optimization, diffraction improved from 3.5 to 1.3 Å resolution. The crystals belong to space group P21, with unit-cell parameters a = 42.6, b = 72.6, c = 62.0 Å, β = 104.5°. The asymmetric unit contains one biological dimer, with 167 amino acids per protomer. A soak with a transition-state analogue is also described. [ABSTRACT FROM AUTHOR]

The title compound, tetra­sodium bis­[tris­(salicylato­titanate(IV)] undeca­hydrate, Na4[Ti(C7H4O3)3]2·11H2O, crystallizes with two titanium salicylate complex ions, four sodium ions and 11 water mol­ecules in the asymmetric unit. One water O atom is disordered over two positions, having 0.74 (5) and 0.26 (5) occupancy. Both Ti atoms and three sodium ions adopt a distorted octa­hedral coordination by O atoms. The fourth sodium ion has a distorted trigonal–bipyramidal coordination by oxygen, sharing one edge with a sodium coordination octa­hedron. [ABSTRACT FROM AUTHOR]

The synthetic steroid 21-acet­oxy-17α-4-pregnene-3,20-dione, C23H32O4, crystallizes with a single mol­ecule in the asymmetric unit. The mol­ecule contains four fused rings, typical of steroids. The cyclo­hexene ring A has nearly the conformation of a boat. One saturated six-membered ring, B, is inter­mediate between chair and half-chair conformations, while the other six-membered ring, C, is essentially a chair. The five-membered ring D tends towards a twist conformation. The ring junction A/ B is quasi- trans, whereas the ring junctions B/ C and C/ D are both trans. The mol­ecule is slightly convex towards the β side. [ABSTRACT FROM AUTHOR]

Intra­molecular hydrogen bonds influence the mol­ecular conformation of the title compound, C10H19N5O, resulting in an extended planar hydrogen-bonded heterocyclic ring structure. The bulky diethyl­amino­ethyl group adopts a butterfly conformation. The stabilization of the crystal structure is supported by an extensive network of inter­molecular hydrogen bonds. [ABSTRACT FROM AUTHOR]

The title compound, C12H13N4+·C7H7O3S−, contains an imidazolium cation and a toluene- p-sulfonate anion in the asymmetric unit. Hydrogen-bonded dimers are formed between the cyano and amino groups of inversion-related imidazolium cations. [ABSTRACT FROM AUTHOR]

The synthesis and crystal structure of thermochromic, yellow benzimidazolium tetrachlorocuprate(II), (C7H7N2)2CuCl4 (1), have been reported. The compound crystallizes in the C2/c space group and contains discrete tetrahedral CuCl4 2− species. It absorbs one molecule of water from humid atmosphere at room temperature to produce a hydrated green form, (C7H7N2)2CuCl4·H2O, which upon heating loses the water molecule in two steps to form the anhydrous yellow compound 1. The role of the water molecule on the solid state, yellow⇋green thermochromic transformation is discussed. [Copyright &y& Elsevier]

Cardiac disease remains the leading cause of morbidity and mortality worldwide. The β 1 -adrenergic receptor (β 1 -AR) is a major regulator of cardiac functions and is downregulated in the majority of heart failure cases. A key physiological process is the activation of heterotrimeric G-protein Gs by β 1 -ARs, leading to increased heart rate and contractility. Here, we use cryo-electron microscopy and functional studies to investigate the molecular mechanism by which β 1 -AR activates Gs. We find that the tilting of α5-helix breaks a hydrogen bond between the sidechain of His373 in the C-terminal α5-helix and the backbone carbonyl of Arg38 in the N-terminal αN-helix of Gα s . Together with the disruption of another interacting network involving Gln59 in the α1-helix, Ala352 in the β6-α5 loop, and Thr355 in the α5-helix, these conformational changes might lead to the deformation of the GDP-binding pocket. Our data provide molecular insights into the activation of G-proteins by G-protein-coupled receptors., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Nicotinic acetylcholine receptors (nAChR) are pentameric ligand gated ion channels whose activity can be modulated by endogenous neurotransmitters as well as by synthetic ligands that bind the same or distinct sites from the natural ligand. The subtype of α7 nAChR has been considered as a potenial therapeutic target for Alzheimer's disease, schizophrenia and other neurological and psychiatric disorders. Here we have developed a homology model of α7 nAChR based on two high resolution crystal structures with Brookhaven Protein Data Bank (PDB) codes 2QC1 and 2WN9 for threading on one monomer and then for building a pentamer, respectively. A number of small molecule binding sites are identified using Pocket Finder (J. An, M. Tortov, and R. Abagyan, Molecular & Cellular Proteomics, 4.6, 752-761 (2005)) of Internal Coordinate Mechanics (ICM). Remarkably, these computer-identified sites match perfectly with ordered solvent densities found in the high-resolution crystal structure of α1 nAChR, suggesting that the surface cavities in the α7 nAChR model are likely binding sites of small molecules. A high throughput virtual screening by flexible ligand docking of 5008 small molecule compounds was performed at three potential allosteric modulator (AM) binding sites of α7 nAChR using Molsoft ICM software (R. Abagyan, M. Tortov and D. Kuznetsov, J Comput Chem 15, 488-506, (1994)). Some experimentally verified allosteric modulators of α7 like CCMI comp-6, LY 7082101, 5-HI, TQS, PNU-120596, genistein, and NS-1738 ranked among top 100 compounds, while the rest of the compounds in the list could guide further search for new allosteric modulators.

The presence of exported chorismate mutases produced by certain organisms such as Mycobacterium tuberculosis has been shown to correlate with their pathogenicity. As such, these proteins comprise a new group of promising selective drug targets. Here, we report the high-resolution crystal structure of the secreted dimeric chorismate mutase from M. tuberculosis (*MtCM; encoded by Rv1885c), which represents the first 3D-structure of a member of this chorismate mutase family, termed the AroQ(gamma) subclass. Structures are presented both for the unliganded enzyme and for a complex with a transition state analog. The protomer fold resembles the structurally characterized (dimeric) Escherichia coli chorismate mutase domain, but exhibits a new topology, with helix H4 of *MtCM carrying the catalytic site residue missing in the shortened helix H1. Furthermore, the structure of each *MtCM protomer is significantly more compact and only harbors one active site pocket, which is formed entirely by one polypeptide chain. Apart from the structural model, we present evidence as to how the substrate may enter the active site.