Crystal Structure Of Complex Research Articles

A biophysical framework for double-drugging kinases

Selective orthosteric inhibition of kinases has been challenging due to the conserved active site architecture of kinases and emergence of resistance mutants. Simultaneous inhibition of distant orthosteric and allosteric sites, which we refer to as "double-drugging", has recently been shown to be effective in overcoming drug resistance. However, detailed biophysical characterization of the cooperative nature between orthosteric and allosteric modulators has not been undertaken. Here, we provide a quantitative framework for double-drugging of kinases employing isothermal titration calorimetry, Förster resonance energy transfer, coupled-enzyme assays, and X-ray crystallography. We discern positive and negative cooperativity for Aurora A kinase (AurA) and Abelson kinase (Abl) with different combinations of orthosteric and allosteric modulators. We find that a conformational equilibrium shift is the main principle governing cooperativity. Notably, for both kinases, we find a synergistic decrease of the required orthosteric and allosteric drug dosages when used in combination to inhibit kinase activities to clinically relevant inhibition levels. X-ray crystal structures of the double-drugged kinase complexes reveal the molecular principles underlying the cooperative nature of double-drugging AurA and Abl with orthosteric and allosteric inhibitors. Finally, we observe a fully closed conformation of Abl when bound to a pair of positively cooperative orthosteric and allosteric modulators, shedding light on the puzzling abnormality of previously solved closed Abl structures. Collectively, our data provide mechanistic and structural insights into rational design and evaluation of double-drugging strategies.

Functional characterization and structural basis of a reversible glycosyltransferase involves in plant chemical defence.

Plants experience numerous biotic stresses throughout their lifespan, such as pathogens and pests, which can substantially affect crop production. In response, plants have evolved various metabolites that help them withstand these stresses. Here, we show that two specialized metabolites in the herbaceous perennial Belamcanda chinensis, tectorigenin and its glycoside tectoridin, have diverse defensive effects against phytopathogenic microorganisms and antifeeding effects against insect pest. We further functionally characterized a 7-O-uridine diphosphate glycosyltransferase Bc7OUGT, which catalyses a novel reversible glycosylation of tectorigenin and tectoridin. To elucidate the catalytic mechanisms of Bc7OUGT, we solved its crystal structure in complex with UDP and UDP/tectorigenin respectively. Structural analysis revealed the Bc7OUGT possesses a narrow but novel substrate-binding pocket made up by plentiful aromatic residues. Further structure-guided mutagenesis of these residues increased both glycosylation and deglycosylation activities. The catalytic reversibility of Bc7OUGT was also successfully applied in an one-pot aglycon exchange reaction. Our findings demonstrated the promising biopesticide activity of tectorigenin and its glycosides, and the characterization and mechanistic study of Bc7OUGT could facilitate the design of novel reversible UGTs to produce valuable glycosides with health benefits for both plants and humans.

Phase equilibria in the Ag8SiSe6-Ag8SiTe6 system and characterization of the solid solutions Ag8SiSe6-xTex

Due to polymorphism and complex crystal structure, compounds of the argyrodite family and phases based on them exhibit several interesting functional properties, such as thermoelectric, photoelectric, optical, as well as ionic conductivity for Cu+ and Ag+ cations. The paper presents the results of the study of phase equilibria in the Ag8SiSe6-Ag8SiTe6 system by DTA, XRD, and SEM methods. Refined data on the melting temperature (1278 K) and polymorphic transitions (315 K and 354 K) of the Ag8SiSe6 compound are presented. The crystallographic parameters of LT-Ag8SiSe6 (Cubic, F-43m, a = 1.0965 nm) and IT-Ag8SiSe6 (Cubic, P4232, a = 1.0891 nm) are also determined. It has been established that the investigated system is quasi-binary and its phase diagram is characterized by the formation of a continuous series of substitutional solid solutions between HT-Ag8SiSe6 and Ag8SiTe6. This process is accompanied by a strong decrease in the temperatures of polymorphic transformations of Ag8SiSe6, which leads to the stabilization of the ion-conducting cubic phase at room temperature in the >10 mol% Ag8SiTe6 compositions area. The crystal lattice parameters of the synthesized solid solutions are calculated by indexing the powder diffraction patterns. The stabilization of the high-temperature cubic phase at room temperature achieved by us presents new opportunities for the development of environmentally friendly thermoelectrics and ion-electronic conductors based on silicon argyrodites with desired composition and properties.

Synthesis and characterization of phenoxy-bridged copper(II) complexes: Structural features, magnetic, thermal and redox properties, and theoretical studies

Three phenoxy-bridged Cu(II) complexes, atrinuclear partial cubane type Cu(II) complex [Cu3(L1)3(µ3-OH)](ClO4)2 (1) (where L1H = (E)-2-(((2-aminoethyl)imino)methyl)-5-(diethylamino) phenol) and two dinuclear Cu(II) complexes, [Cu(L2)(MeOH)(OMe)]2 (2)and [Cu(sal)(bipy)(ClO4)]2 (3) (where L2H = (E)-N'-(5-bromo-2-hydroxybenzylidene) benzohydrazide), sal = 5-Bromo salicylaldehyde, bipy = 2,2-Bipyridine) were synthesized via in-situ reaction and have been successfully characterized both experimentally and computationally. In an in-situ reaction, the Schiff base formed (L1H/L2H) behaves as tridentate ligands having ONO donor sites. The structures of Cu(II) complexes(1)-(3)were established by X-ray crystallography. In the trinuclear Cu(II) complex(1), the three phenoxy oxygen atoms of ligand L1 bridge the Cu(II) center ions in µ3-fashion, while in dinuclear Cu(II) complexes (2)and(3), the phenoxy oxygen bridges the Cu(II) center ionsin µ2-fashion. The temperature dependence magnetic susceptibility, thermal gravimetric analysis (TGA) and cyclic voltammetry analysis were performed for Cu(II) complexes(1)-(3). Hirshfeld surface analysis and 2D fingerprint plots have also been explored in the crystal structure of complexes.

Design and structural optimization of thiadiazole derivatives with potent GLS1 inhibitory activity

GLS1 is an attractive target not only as anticancer agents but also as candidates for various potential pharmaceutical applications such as anti-aging and anti-obesity treatments. We performed docking simulations based on the complex crystal structure of GLS1 and its inhibitor CB-839 and found that compound A bearing a thiadiazole skeleton exhibits GLS1 inhibition. Furthermore, we synthesized 27 thiadiazole derivatives in an effort to obtain a more potent GLS1 inhibitor. Among the synthesized derivatives, 4d showed more potent GLS1 inhibitory activity (IC50 of 46.7 µM) than known GLS1 inhibitor DON and A. Therefore, 4d is a very promising novel GLS1 inhibitor.

Influence of Quantum Effects on Dielectric Relaxation in Functional Electrical and Electric Energy Elements Based on Proton Semiconductors and Dielectrics

Using the quasi-classical kinetic theory of dielectric relaxation, in addition to existing methods, fundamental mathematical expressions are built, which make it possible to more strictly consider the effects of the main charge carriers’ (protons’) tunneling on the numerical values of the molecular parameters (activation energy, equilibrium concentration) of protons in HBC. The formulas for calculating the statistically averaged non-stationary quantum transparency of a parabolic potential barrier for protons have been modernized by more stringent consideration of the effects of corrections caused by an external electric field. For the model of a double-symmetric potential well, a generalized nonlinear solution of the quasi-classical kinetic equation of dielectric relaxation in HBC was built. The phenomenological Bucci-Rive formula for thermally stimulated depolarization current density (TSDC) was first investigated, taking into account quantum transparency, for the case of a parabolic potential barrier. The choice of the parabolic shape of the potential barrier allowed, at a theoretical level, for the mathematical model of relaxation polarization to be brought closer to the conditions of the real spatial structure of the crystal potential field, in comparison with the rectangular potential barrier model. It has been found that quantum effects due to proton tunnel transitions significantly affect the mechanism of thermally stimulated depolarization currents in HBC, over a wide temperature range (50–550 K) and external field parameters (0.1–1 MV/m). Generalized solutions of the nonlinear kinetic equation, recorded considering the effects of field parameters on proton tunnel transitions, made it possible to significantly approximate the theoretical values of activation energies, equilibrium concentrations of protons and amplitudes of the theoretical maxima of the current density of thermally stimulated depolarization, according to their experimental values in the field of low-temperature (50–100 K) and high-temperature (350–550 K) maxima of TSDC density in HBC. For the first time, precision measurements of TSDC temperature spectra were carried out for chalcanthite crystals. The effects of alloying impurities concentrations and crystal calcination temperatures on the parameters of experimental maxima in the TSDC spectrum of chalcanthite were established. A physical mechanism of the quantum tunnel motion of protons in HBC with a complex crystal structure (crystalline hydrates, layered silicates, ferroelectric HBC (KDP, DKDP)) is described. The patterns found in this article indicate a fairly high degree of applied scientific significance for the obtained theoretical results, allowing for the further development of electrophysics and optoelectronics of heterogeneous structures (MIS, MSM) based on proton semiconductors and dielectrics (PSD) and their composites.

Synthesis and anti-tumor activity of piperonal substituted chalcone

Objectives: Chalcones have been identified as potential antitumor agents with a novel target, the tubulin. The aim of the study was to synthesize a piperonal substituted chalcone and evaluate its in vivo antitumor activity. Materials and Methods: Piperonal substituted chalcone was synthesized using Claisen-Schmidt condensation and characterized using various spectroscopic techniques. The lethal dose (LD50) of the synthesized compound was estimated using OECD-425 guidelines in rats. Antitumor activity of the synthesized compound was evaluated on 1-methyl nitrosourea (MNU)-induced mammary tumor in female Wistar rats. Histological evaluation was used to confirm tumor induction and assess treatment with the synthesized compound. The possible mechanism of action of the synthesized compound was elucidated in silico using molecular docking. Results: The compound was synthesized and named C2. C2 was found to be relatively safe with LD50 >2000 mg/kg orally. Moreover, C2 exhibited remarkable antitumor activity, at all the tested doses in a dose dependent manner. Histological evaluation of the MNU-induced mammary tumor rats treated with C2 displayed fewer signs of hyperplasia and small numbers of connective tissue with larger lobules when compared with the untreated group. In silico tubulin-binding interactions revealed that the kinetics of C2 binding to tubulin was like that of colchicine. Comparison of crystal structures of tubulin-C2 and tubulin-colchicine complexes showed that the binding mode of C2 to tubulin was like that of colchicine to tubulin and produced the same conformational changes on the tubulin structure as colchicine. Conclusion: The synthesized chalcone demonstrated remarkable antitumor activities in MNU-induced mammary tumors in rats possibly through inhibition of tubulin polymerization.

C3-symmetric tritopic ligand derived trinuclear dioxovanadium(V) complexes with different counter cations: Synthesis and X-ray structures

Two square pyramidal trinuclear dioxovanadium(V) complexes with [N2O3]-donor set ligand environment 1, (Et3NH)2[V3O6(SaltagBr)] {H5SaltagBr = tris(5‑bromo-2-hydroxybenzylidene)triaminoguanidine} and 2, (n-Bu4N)2[V3O6(SaltagBr)] have been synthesized and the X-ray structures of both 1•H2O and 2•H2O have been determined. SaltagBr is a pentaanionic tritopic ligand with C3-symmetry containing three [NNO]-donor set tridentate pockets, thereby making it a suitable ligand for holding three VO2+ groups in their pockets. Crystal packing in the complex 1•H2O, (Et3NH)2[V3O6(SaltagBr)]•H2O is partially stabilized by intermolecular H-bonds and intermolecular π-π stacking interactions between the phenyl rings with a centroid-to-centroid distance of 3.700 Å. In the crystal structure of complex 2•H2O, (n-Bu4N)2[V3O6(SaltagBr)]•H2O, intermolecular H-bonds partially contribute to the stabilization of crystal packing.

Machine learning-based classification models for non-covalent Bruton's tyrosine kinase inhibitors: predictive ability and interpretability.

In this study, we built classification models using machine learning techniques to predict the bioactivity of non-covalent inhibitors of Bruton's tyrosine kinase (BTK) and to provide interpretable and transparent explanations for these predictions. To achieve this, we gathered data on BTK inhibitors from the Reaxys and ChEMBL databases, removing compounds with covalent bonds and duplicates to obtain a dataset of 3895 inhibitors of non-covalent. These inhibitors were characterized using MACCS fingerprints and Morgan fingerprints, and four traditional machine learning algorithms (decision trees (DT), random forests (RF), support vector machines (SVM), and extreme gradient boosting (XGBoost)) were used to build 16 classification models. In addition, four deep learning models were developed using deep neural networks (DNN). The best model, Model D_4, which was built using XGBoost and MACCS fingerprints, achieved an accuracy of 94.1% and a Matthews correlation coefficient (MCC) of 0.75 on the test set. To provide interpretable explanations, we employed the SHAP method to decompose the predicted values into the contributions of each feature. We also used K-means dimensionality reduction and hierarchical clustering to visualize the clustering effects of molecular structures of the inhibitors. The results of this study were validated using crystal structures, and we found that the interaction between the BTK amino acid residue and the important features of clustered scaffold was consistent with the known properties of the complex crystal structures. Overall, our models demonstrated high predictive ability and a qualitative model can be converted to a quantitative model to some extent by SHAP, making them valuable for guiding the design of new BTK inhibitors with desired activity.

Effects of water molecules on luminescence in europium and terbium coordination polymers with p-fluorobenzoic acid as ligand

Our previous experimental observations show that the crystal structure of lanthanide luminescent complexes synthesized in aqueous solution usually contains a large number of coordination water molecules or free water molecules. In order to probe the influence of water molecules on luminescent processes of lanthanide complexes, the photoluminescence properties of Ln-FBA (Ln = Eu and Tb, FBA = p-fluorobenzoic acid) coordination polymers at different ambient temperatures, in different solvents and aqueous DMSO solutions with different volume concentrations were systematically investigated. The experiment results show that the presence of water molecules can promote the energy transfer from FBA ligand to Ln3+, at the same time, can cause luminescent non-radiation quenching of lanthanide ions. In addition, the variation of emission intensity ratio of 615 nm/591 nm peaks of Eu3+ with increasing the volume concentration of H2O can be potentially used for the quantitatively detection of water traces in organic solvents. In order to suppress the non-radiation quenching caused by the water molecules, Ln-FBA (Ln = Eu and Tb) coordination polymers were embedded into the PVP matrix to prepare Ln-FBA@PVP hybrid materials. The photoluminescence investigation indicates that PVP can not only block the quenching effect of water molecules on luminescence, but also effectively sensitize Eu3+ and Tb3+ luminescence. These experimental conclusions are useful for probing the influence of water molecules on luminescent processes of lanthanide complexes, quantitatively detecting water traces in organic solvents and enhancing the photoluminescence intensity in lanthanide complexes.

Anisotropic Collective Variables with Machine Learning Potential for Ab Initio Crystallization of Complex Ceramics.

Enhanced sampling molecular dynamics (MD) simulations have been extensively used in the phase transition study of simple crystalline materials, such as aluminum, silica, and ice. However, MD simulation of the crystallization process for complex crystalline materials still faces a formidable challenge due to their multicomponent induced multiphase problem. Here, we realize the ab initio accuracy MD crystallization simulations of complex ceramics by using anisotropic collective variables (CVs) and machine learning (ML) potential. The anisotropic X-ray diffraction intensity CVs provide precise identification of complex crystal structures with detailed crystallography information, while the ML potential makes it feasible to further perform enhanced sampling simulations with ab initio accuracy. We verify the universality and accuracy of this method through complex ceramics with three kinds of representative structures, i.e., Ti3SiC2 for the MAX structure, zircon for the mineral structure, and lead zirconate titanate for the perovskite structure. It demonstrates exceptional efficiency and ab initio quality in achieving crystallization and generating free energy surfaces of all these ceramics, facilitating the analysis and design of complex crystalline materials.

Synthesis and X-ray crystal structures of mononuclear and multinuclear metal complexes of 3-substituted 4-cyanopyrazole ligands

Complexes of pyrazole ligands with a cyano substituent in the 4-position and alkyl or aryl substituents in the 3-position are reported, including mononuclear {M(HpzR,4CN)4X2 (X = Cl, M = Ni, R = t-Bu, c-Pr, Cy, Et; X = Cl, M = Co, R = Et, Cy, t-Bu; X = Br, M = Ni, R = i-Pr), [Pt(Hpzt-Bu,4CN)2Cl4], [Cu(HpzEt,4CN)2(H2O)2(NO3)2], M(HpzR,4CN)2Cl2 (M = Pt, Pd; R = t-Bu), [Pd(HpztBu,4CN)2Br2], [Pd(HpzPh2)2Cl2]}, dinuclear {(NEt4)2{Ni(pztBu,4CN)2(μ-pztBu,4CN)}2, {Pd(HpzPh2)(μ-pzPh2)Br}2}, and trinuclear {Ni3(pzPh)6, Pd3(pzPh,4CN)6} complexes, as well as a novel octanuclear complex {(NEt4)2[Ni8(pzPh,4CN)8Cl4(OH)6]}. Computational analysis is utilized to address the observation of only one isomer of tetrakis(pyrazole)dihalometal complexes. X-ray crystal structures are reported for two new pyrazoles and 18 metal complexes.

Molecular Dynamics and Machine Learning Study of Adrenaline Dynamics in the Binding Pocket of GPCR.

G-protein coupled receptors (GPCRs) are the most prominent family of membrane proteins that serve as major targets for one-third of the drugs produced. A detailed understanding of the molecular mechanism of drug-induced activation and inhibition of GPCRs is crucial for the rational design of novel therapeutics. The binding of the neurotransmitter adrenaline to the β2-adrenergic receptor (β2AR) is known to induce a flight or fight cellular response, but much remains to be understood about binding-induced dynamical changes in β2AR and adrenaline. In this article, we examine the potential of mean force (PMF) for the unbinding of adrenaline from the orthosteric binding site of β2AR and the associated dynamics using umbrella sampling and molecular dynamics (MD) simulations. The calculated PMF reveals a global energy minimum, which corresponds to the crystal structure of β2AR-adrenaline complex, and a meta-stable state in which the adrenaline is moved slightly deeper into the binding pocket with a different orientation compared to that in the crystal structure. The orientational and conformational changes in adrenaline during the transition between these two states and the underlying driving forces of this transition are also explored. Based on the clustering of MD configurations and machine learning-based statistical analyses of time series of relevant collective variables, the structures and stabilizing interactions of these two states of the β2AR-adrenaline complex are also investigated.

Synthesis of sandwich metallaboranes [M(B11H11)2]3– (M = Cu, Ag) via polyhedral expansion of the closo-undecaborate anion [B11H11]2–

Reactions of the undecahydro-closo-undecaborate anion [B11H11]2– with copper(I) and silver(I) complexes [(Ph3P)3MX] (M = Cu, X = Cl; M = Ag, X = NO3) were found to result in the polyhedral expansion with the formation of the corresponding metallaboranes (Bu4N)3[commo-M(B11H11)2] rather than the M–H–B complexes typical of borane ligands. The crystal structure of complex (Bu4N)3[Ag(B11H11)2] was determined by single-crystal X-ray diffraction. Hirschfeld surface analysis and DFT calculations for both metallaboranes [M(B11H11)2]3– (M = Cu, Ag) were carried out.

Design, Synthesis and Structure-Activity Relationship Studies of Protein Kinase CK2 Inhibitors Containing a Purine Scaffold.

Protein kinase CK2 (CK2) is involved in the suppression of gene expression, protein synthesis, cell proliferation, and apoptosis, thus making it a target protein for the development of therapeutics toward cancer, nephritis, and coronavirus disease 2019. Using the solvent dipole ordering-based method for virtual screening, we identified and designed new candidate CK2α inhibitors containing purine scaffolds. Virtual docking experiments supported by experimental structure-activity relationship studies identified the importance of the 4-carboxyphenyl group at the 2-position, a carboxamide group at the 6-position, and an electron-rich phenyl group at the 9-position of the purine scaffold. Docking studies based on the crystal structures of CK2α and inhibitor (PDBID: 5B0X) successfully predicted the binding mode of 4-(6-carbamoyl-8-oxo-9-phenyl-8,9-dihydro-7H-purin-2-yl) benzoic acid (11), and the results were used to design stronger small molecule targets for CK2α inhibition. Interaction energy analysis suggested that 11 bound around the hinge region without the water molecule (W1) near Trp176 and Glu81 that is frequently reported in crystal structures of CK2α inhibitor complexes. X-ray crystallographic data for 11 bound to CK2α was in very good agreement with the docking experiments, and consistent with activity. From the structure-activity relationship (SAR) studies presented here, 4-(6-Carbamoyl-9-(4-(dimethylamino)phenyl)-8-oxo-8,9-dihydro-7H-purin-2-yl) benzoic acid (12) was identified as an improved active purine-based CK2α inhibitor with an IC50 of 4.3 µM. These active compounds with an unusual binding mode are expected to inspire new CK2α inhibitors and the development of therapeutics targeting CK2 inhibition.

Coordination Number in High-Spin-Low-Spin Equilibrium in Cluster Models of the S2 State of the Oxygen Evolving Complex.

The S2 state of the Oxygen Evolving Complex (OEC) of Photosystem II (PSII) shows high-spin (HS) and low-spin (LS) EPR signals attributed to distinct structures based on computation. Five-coordinate MnIII centers are proposed in these species but are absent in available spectroscopic model complexes. Herein, we report the synthesis, crystal structure, electrochemistry, SQUID magnetometry, and EPR spectroscopy of a MnIIIMnIV3O4 cuboidal complex featuring five-coordinate MnIII. This cluster displays a spin ground state of S = 5/2, while conversion to a six-coordinate Mn upon treatment with water results in a spin state change to S = 1/2. These results demonstrate that coordination number, without dramatic changes within the Mn4O4 core, has a substantial effect on spectroscopy.

Structural evolution of an immune evasion determinant shapes pathogen host tropism

Modern infectious disease outbreaks often involve changes in host tropism, the preferential adaptation of pathogens to specific hosts. The Lyme disease-causing bacterium Borrelia burgdorferi (Bb) is an ideal model to investigate the molecular mechanisms of host tropism, because different variants of these tick-transmitted bacteria are distinctly maintained in rodents or bird reservoir hosts. To survive in hosts and escape complement-mediated immune clearance, Bb produces the outer surface protein CspZ that binds the complement inhibitor factor H (FH) to facilitate bacterial dissemination in vertebrates. Despite high sequence conservation, CspZ variants differ in human FH-binding ability. Together with the FH polymorphisms between vertebrate hosts, these findings suggest that minor sequence variation in this bacterial outer surface protein may confer dramatic differences in host-specific, FH-binding-mediated infectivity. We tested this hypothesis by determining the crystal structure of the CspZ-human FH complex, and identifying minor variation localized in the FH-binding interface yielding bird and rodent FH-specific binding activity that impacts infectivity. Swapping the divergent region in the FH-binding interface between rodent- and bird-associated CspZ variants alters the ability to promote rodent- and bird-specific early-onset dissemination. We further linked these loops and respective host-specific, complement-dependent phenotypes with distinct CspZ phylogenetic lineages, elucidating evolutionary mechanisms driving host tropism emergence. Our multidisciplinary work provides a novel molecular basis for how a single, short protein motif could greatly modulate pathogen host tropism.

BiSbSe3: A promising Te-free thermoelectric material

BiSbSe3 is a Te-free thermoelectric material with a chain-like complex crystal structure and multiple band configuration. This work overviews recent advancements in BiSbSe3, clearly demonstrating its excellent thermal and electrical characteristics. The strategies to optimize the thermoelectric performance of BiSbSe3 mainly focus on two aspects: manipulating carrier concentration and effective mass based on multiple conduction bands, and elevating carrier mobility based on maneuvering electrical parameters and microstructures. Additionally, strategies for boosting the carrier mobility are outlined as the prospects for the future development of BiSbSe3, including sharpening bands, improving orientation, and designing composites.

Nanostructured TLDs: Studying the impact of crystalline size on the Thermoluminescence glow-curve shape and electron trapping parameters

Nanostructured thermoluminescent dosimeters (TLDs) and their relevance in the field of Stimulated Luminescence has grown over the past years. Particularly, since preparation methods and characterization techniques have been improved, while their integration in technological advancements which has also significantly increased. Despite the numerous case studies dealing with applications and properties of nanomaterials, there is a limited number of studies investigating cases from a basic research point of view, like studying the transition of a material from bulk to nanoscale and the dominant features of this transition. Specifically, in Thermally Stimulated Luminescence or Thermoluminescence (TL), the extensive study via geometrical signal processing with the well-established techniques of Peak Shape Methods (PSM) and Computerized Glow-Curve Deconvolution (CGCD), and the estimation of trapping parameters of certain TL peaks, along with possible dependence of the activation energy of electron traps inside the crystal structure for different crystalline sizes, are missing from the literature. The present study includes several popular TLDs like BeO, LiF, CaSO4 and other more complex crystal structures such as NaLi2PO4, K2Ca2(SO4)3, LiNaSO4 and a geological Fluorapatite in different crystalline size fractions. Special emphasis has been devoted to the estimation of activation energies and the geometrical characteristics in the nanoscale by analyzing each TL signal accordingly. While the analysis imposes several interesting cases on the implementation of the results, the study has shown that under different crystalline sizes, most of materials follow a normal downtrend on their signal with some insignificant alterations on their physical parameters.

New structures of Class II Fructose-1,6-Bisphosphatase from Francisella tularensis provide a framework for a novel catalytic mechanism for the entire class.

Class II Fructose-1,6-bisphosphatases (FBPaseII) (EC: 3.1.3.11) are highly conserved essential enzymes in the gluconeogenic pathway of microorganisms. Previous crystallographic studies of FBPasesII provided insights into various inactivated states of the enzyme in different species. Presented here is the first crystal structure of FBPaseII in an active state, solved for the enzyme from Francisella tularensis (FtFBPaseII), containing native metal cofactor Mn2+ and complexed with catalytic product fructose-6-phosphate (F6P). Another crystal structure of the same enzyme complex is presented in the inactivated state due to the structural changes introduced by crystal packing. Analysis of the interatomic distances among the substrate, product, and divalent metal cations in the catalytic centers of the enzyme led to a revision of the catalytic mechanism suggested previously for class II FBPases. We propose that phosphate-1 is cleaved from the substrate fructose-1,6-bisphosphate (F1,6BP) by T89 in a proximal α-helix backbone (G88-T89-T90-I91-T92-S93-K94) in which the substrate transition state is stabilized by the positive dipole of the 〈-helix backbone. Once cleaved a water molecule found in the active site liberates the inorganic phosphate from T89 completing the catalytic mechanism. Additionally, a crystal structure of Mycobacterium tuberculosis FBPaseII (MtFBPaseII) containing a bound F1,6BP is presented to further support the substrate binding and novel catalytic mechanism suggested for this class of enzymes.