Hen egg-white lysozyme crystallisation: protein stacking and structure stability enhanced by a Tellurium(VI)-centred polyoxotungstate

From Self-Assembly to Drug Delivery: Understanding and Exploring Protein Fibrils

It is crucial to comprehend protein misfolding and aggregation in the domains of biomedicine, pharmaceuticals, and proteins. Amyloid fibrils are formed when proteins misfold and assemble, resulting in the debilitating illness known as "amyloidosis". This work investigates lysozyme fibrillation with pluronics (F68 and F127). The effect of pluronics on protein aggregation and fibrillation has been studied mechanistically using a combination of calorimetric and spectroscopic techniques. TEM images and the ThT binding experiment were used to analyze the conformation of protein fibrils, and the results showed that pluronics accelerated the fibrillation process. When pluronics interact with protein at different stages of fibrillation, their pre- and postmicellar concentrations show a decrease in ΔHm° value as the time of incubation increases. This indicates the formation of amorphous aggregates due to which endothermic enthalpy is observed. As a consequence, it was investigated if these generated aggregates can also act as drug delivery vehicle; therefore, the work was carried out with 5-fluorouracil and cytarabine. The endothermic enthalpy of interaction suggests that hydrophobic interaction is more prevalent when cytarabine is employed with protein fibrils, whereas the electrostatic interaction is more prevalent when 5-fluorouracil is combined with it. The former drug, however, showed a greater adsorption than the latter on the surface of protein fibrils. It is therefore determined that 5-fluorouracil has relatively significant adsorption on fibril surfaces, whereas cytarabine has weak adsorption and is easily desorbed in cells. Consequently, the combination of LFF127 and 5-FU is lethal to malignant cells. The drug encapsulation and delivery aspect of protein fibrils/aggregates needs further exploration.

Discrete Hybrid Vanadium-oxo Cluster as a Targeted Tool for Selective Protein Oxidative Modifications and Cleavage

Understanding the impact of oxidative modification on protein structure and functions is essential for developing therapeutic strategies to combat macromolecular damage and cell death. However, selectively inducing oxidative modifications in proteins under physiological conditions remains challenging. Herein we demonstrate that [V6O13{(OCH2)3CCH2OH}2]2- (V6-OH) hybrid metal-oxo cluster can be used for selective protein oxidative cleavage and modifications. We present the first example of a protein-bound hybrid vanadate cluster, where its interactions with protein surfaces and the redox activity of vanadium enable selective oxidative modifications. Single Crystal X-ray Diffraction (SC-XRD) of the V6-OH and hen egg white lysozyme (HEWL) complex revealed that the binding is dictated both by the inorganic core and the organic ligands attached to it. Selective oxidation or cleavage of HEWL occurs under physiological conditions by producing reactive oxygen species (ROS) in presence of ascorbate (Asc) as a reducing agent. The outcome of the oxidative reaction can be tuned by varying the concentration of V6-OH to result either in selective oxidation of the amino acid side chains or peptide bond cleavage. LC-MS and crystallography revealed that oxidative modifications were mainly concentrated near the cluster binding sites, providing spatial control of ROS production. This study advances our understanding of vanadium's role in biological systems and demonstrates the potential of hybrid metal-oxo clusters in protein modification.

Fine-tuning non-covalent interactions between hybrid metal-oxo clusters and proteins

Interactions between the protein Hen Egg White Lysozyme (HEWL) and three different hybrid Anderson-Evans polyoxometalate clusters - AE-NH2 (δ-[MnMo6O18{(OCH2)3CNH2}2]3-), AE-CH3 (δ-[MnMo6O18{(OCH2)3CCH3}2]3-) and AE-Biot (δ-[MnMo6O18{(OCH2)3CNHCOC9H15N2OS}2]3-) - were studied via tryptophan fluorescence spectroscopy and single crystal X-ray diffraction. Quenching of tryptophan fluorescence was observed in the presence of all three hybrid polyoxometalate clusters (HPOMs), but the extent of quenching and the binding affinity were greatly dependent on the nature of the organic groups attached to the cluster. Control experiments further revealed the synergistic effect of the anionic polyoxometalate core and organic ligands towards enhanced protein interactions. Furthermore, the protein was co-crystallised with each of the three HPOMs, resulting in four different crystal structures, thus allowing for the binding modes of HPOM-protein interactions to be investigated with near-atomic precision. All crystal structures displayed a unique mode of binding of the HPOMs to the protein, with both functionalisation and the pH of the crystallisation conditions influencing the interactions. From the crystal structures, it was determined that HPOM-protein non-covalent complexes formed through a combination of electrostatic attraction between the polyoxometalate cluster and positively charged surface regions of HEWL, and direct and water-mediated hydrogen bonds with both the metal-oxo inorganic core and the functional groups of the ligand, where possible. Hence, functionalisation of metal-oxo clusters shows great potential in tuning their interactions with proteins, which is of interest for several biomedical applications.

Speciation atlas of polyoxometalates in aqueous solutions

Speciation is the key parameter in solution chemistry that describes the composition, concentration, and oxidation state of each chemical form of an element present in a sample. The speciation study of complex polyatomic ions has remained challenging because of the large number of factors affecting stability and the limited number of direct methods. To address these challenges, we developed the speciation atlas of 10 polyoxometalates commonly used in catalytic and biological applications in aqueous solutions, where the speciation atlas provides both a species distribution database and a predictive model for other polyoxometalates to be used. Compiled for six different polyoxometalate archetypes with three types of addenda ions based on 1309 nuclear magnetic resonance spectra under 54 different conditions, the atlas has revealed a previously unknown behavior of polyoxometalates that may account for their potency as biological agents and catalysts. The atlas is intended to promote the interdisciplinary use of metal oxides in various scientific fields.

Synthesis and characterization of the `Japanese rice-ball'-shaped Molybdenum Blue Na4[Mo2O2(OH)4(C6H4NO2)2]2[Mo120Ce6O366H12(OH)2(H2O)76]∼200H2O

The hybridized lanthanide-containing molybdenum blue (Ln-MB) wheel Na4[Mo2O2(OH)4(C6H4NO2)2]2[Mo120Ce6O366H12(OH)2(H2O)76]∼200H2O ({Mo2(C6H4NO2)2}2{Mo120Ce6}) was assembled in an aqueous one-pot synthesis. The Ln-MB was hybridized with 2-picolinic acid through the generation of the organometallic counter-ion [Mo2O2(OH)4(C6H4NO2)2]2+. Control experiments demonstrated that the position of the carboxylic acid group (2-position to the N atom) in the hybridization component is critical in yielding single crystals of Ln-MB. In addition to single-crystal X-ray diffraction (XRD) analysis, which revealed a `Japanese rice-ball'-shaped Ln-MB as the anion, elemental analyses, IR spectroscopy, and thermogravimetric analysis (TGA) were performed to confirm its structure and composition. Bond-valence-sum calculations (BVS) revealed that {Mo2(C6H4NO2)2}2{Mo120Ce6} is composed of a 24-electron reduced anionic ring, which was confirmed by Vis-NIR spectroscopy.

A Novel Anderson-Evans Polyoxometalate-based Metal-organic Framework Composite for the Highly Selective Isolation and Purification of Cytochrome C from Porcine Heart

Anderson-Evans type polyoxometalate group (Na₆[TeW₆O₂₄]·22 H₂O, TeW₆) was combined with porous metal-organic framework ZIF-8 by electrostatic interaction to obtain a novel Anderson-Evans polyoxometalate-based metal-organic framework composite, TeW₆ @ZIF-8. FT-IR, Raman, XRD, TG, DSC, SEM, and TEM were used to characterize the composite. It was proved that the Anderson-Evans type polyoxometalate group TeW₆ was successfully hybridized with metal-organic framework ZIF-8, and the composite possesses good stability. Based on the potential interaction between TeW₆ and proteins and the coordination between imidazole groups in ZIF-8 and proteins with a porphyrin ring structure, the adsorption selectivity towards different proteins on the TeW₆ @ZIF-8 composite was studied in this work. The experiment results showed that the TeW₆ @ZIF-8 composite was selectively adsorbed to cytochrome C. At pH 11.0, the adsorption efficiency of 94.01% was obtained for processing 1.0 mL 100 μg mL^-1 cytochrome C with 3.0 mg TeW₆ @ZIF-8 composite. The adsorption behavior of cytochrome C fits well with the Langmuir adsorption model, corresponding to a theoretical adsorption capacity of 232.56 mg g^-1. The retained cytochrome C could be readily recovered by 1% SDS (m/m), giving rise to a recovery of 65.6%. Circular dichroism spectra indicate no conformational change for cytochrome C after the adsorption and desorption processes, demonstrating the favorable biocompatibility of TeW₆ @ZIF-8 composite. In applying practical samples, SDS-PAGE results showed that cytochrome C was successfully isolated and purified by TeW₆ @ZIF-8 composite from porcine heart protein extract, which is further identified with LC-MS/MS. Thus, a new strategy for separating and purifying cytochrome C from the porcine heart using TeW₆ @ZIF-8 composite as an adsorbent was established.

Conformational flexibility in the zinc solute-binding protein ZnuA

Zinc is an essential metal for all kingdoms of life, making its transport across the cell membrane a critical function. In bacteria, high-affinity zinc import is accomplished by ATP-binding cassette (ABC) transporters, which rely on extracellular solute-binding proteins (SBPs) of cluster A-I to acquire the metal and deliver it to the membrane permease. These systems are important for survival and virulence, making them attractive targets for the development of novel antibiotics. Citrobacter koseri is an emerging pathogen with extensive antibiotic resistance. High-affinity zinc binding to the C. koseri cluster A-I SBP ZnuA has been characterized and the structure of the zinc-bound (holo) form has been determined by X-ray crystallography. Remarkably, despite 95% sequence identity to the ZnuA homologue from Salmonella enterica, C. koseri ZnuA exhibits a different zinc-coordination environment and a closed rather than an open conformation. Comparison with structures of another close ZnuA homologue from Escherichia coli suggests a surprisingly flexible conformational landscape that may be important for efficient zinc binding and/or delivery to the membrane permease.

Lysozyme Improves the Inhibitory Effects of Panax notoginseng Saponins on Phenotype Transformation of Vascular Smooth Muscle Cells by Binding to Ginsenoside Re

Panax notoginseng saponins (PNS) have been used to treat cardiovascular diseases for hundreds of years in China. Lysozyme can bind to exogenous compounds and promote their activity. Nevertheless, knowledge of whether there is a synergistic role between lysozyme and PNS is far from sufficient. In this study, we show that the mixture of PNS and lysozyme synergistically inhibited platelet derived growth factor BB (PDGF-BB)-induced vascular smooth muscle cell (VSMC) viability, and in the five main components of PNS, GS-Re, but not GS-Rb1, NG-R1, GS-Rg1, or GS-Rd, reduced VSMC viability by combined application with lysozyme. Next, the supramolecular complexes formed by GS-Re and lysozyme were detected by mass spectrometry, and the binding ability increased with the concentration ratio of GS-Re to lysozyme from 4:1 to 12:1. In the supramolecular complexes, the relative contents of α-helix of lysozyme were increased, which was beneficial for stabilizing the structure of lysozyme. The 12:1 mixture of GS-Re and lysozyme (12.8 μmol/L GS-Re+1.067 μmol/L lysozyme) repressed PDGF-BB-induced VSMC viability, proliferation, and migration, which were associated with the upregulated differentiated markers and downregulated dedifferentiated markers. Finally, in CaCl₂-induced rodent abdominal aortic aneurysm (AAA) models, we found that the 12:1 mixture of GS-Re and lysozyme slowed down AAA progression and reversed phenotype transformation of VSMCs. Thus, Gs-Re combined with a small amount of lysozyme may provide a novel therapeutic strategy for vascular remodeling-associated cardiovascular diseases.

Speciation of Transition-Metal-Substituted Keggin-Type Silicotungstates Affected by the Co-crystallization Conditions with Proteinase K

We report on the synthesis of the tetrasubstituted sandwich-type Keggin silicotungstates as the pure Na salts Na₁₄[(A-α-SiW₁₀O₃₇)₂{Co₄(OH)₂(H₂O)₂}]·37H₂O (Na{SiW₁₀Co₂}₂) and Na₁₄[(A-α-SiW₁₀O₃₇)₂{Ni₄(OH)₂(H₂O)₂}]·77.5H₂O (Na{SiW₁₀Ni₂}₂), which were prepared by applying a new synthesis protocol and characterized thoroughly in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis. Proteinase K was applied as a model protein and the polyoxotungstate (POT)–protein interactions of Na{SiW₁₀Co₂}₂ and Na{SiW₁₀Ni₂}₂ were studied side by side with the literature-known K₅Na₃[A-α-SiW₉O₃₄(OH)₃{Co₄(OAc)₃}]·28.5H₂O ({SiW₉Co₄}) featuring the same number of transition metals. Testing the solution behavior of applied POTs under the crystallization conditions (sodium acetate buffer, pH 5.5) by time-dependent UV/vis spectroscopy and electrospray ionization mass spectrometry speciation studies revealed an initial dissociation of the sandwich POTs to the disubstituted Keggin anions H_xNa_5–x[SiW₁₀Co₂O₃₈]^3– and H_xNa_5–x[SiW₁₀Ni₂O₃₈]^3– ({SiW₁₀M₂}, M = Co^II and Ni^II) followed by partial rearrangement to the monosubstituted compounds (α-{SiW₁₁Co} and α-{SiW₁₁Ni}) after 1 week of aging. The protein crystal structure analysis revealed monosubstituted α-Keggin POTs in two conserved binding positions for all three investigated compounds, with one of these positions featuring a covalent attachment of the POT anion to an aspartate carboxylate. Despite the presence of both mono- and disubstituted anions in a crystallization mixture, proteinase K selectively binds to monosubstituted anions because of their preferred charge density for POT–protein interaction.

We report on the development of a new synthesis protocol to prepare the Na salts of the tetrasubstituted sandwich-type Keggin derivatives Na₁₄[(A-α-SiW₁₀O₃₈)₂{Co₄(OH)₂(H₂O)₂}]·37H₂O (Na{SiW₁₀Co₂}₂) and Na₁₄[(A-α-SiW₁₀O₃₈)₂{Ni₄(OH)₂(H₂O)₂}]·77.5H₂O (Na{SiW₁₀Ni₂}₂). Following a thorough characterization of the polyoxotungstate (POT) dimers involving single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis in the solid state and UV/vis spectroscopy and electrospray ionization mass spectrometry in solution, the water-soluble compounds (>5 mM) were applied as additives for the crystallization of proteinase K along with the tetrasubstituted monomeric Keggin-type analogue K₅Na₃[A-α-SiW₉O₃₄(OH)₃{Co₄(OAc)₃}]·28.5H₂O ({SiW₉Co₄}). Crystallographic studies on the obtained protein crystals revealed monosubstituted Keggin derivatives in all three cases bound to conserved sites of the protein, which highlights a selectivity of proteinase K toward monosubstituted Keggin POTs within a narrow range of surface charge density.

Anderson-type polyoxometalates: from structures to functions

Anderson-type polyoxometalates (POMs) are one of the most important groups of the POM family. In the past decade, the functionalization of Anderson-type POMs has achieved significant progress and these materials have already shown unique charm in catalysis, molecular devices, energy materials, and inorganic biochemical drugs. In particular, their highly flexible topological structure and diverse functionalization methods make them the most convenient and universal platforms for rational design and controllable synthesis. This review provides a deep discussion on the recent progress in the synthetic methodology, structural exploration, and promising applications of Anderson-type POMs. It also summarizes the latest research directions and provides future prospects.

PtIV- or MoVI-substituted decavanadates inhibit the growth of Mycobacterium smegmatis

Inhibitory effects of two monosubstituted decavanadates by Pt^IV in monoplatino(IV)nonavanadate(V) ([H₂Pt^IVV₉O₂₈]^5-, V₉Pt), and by Mo^IV in monomolybdo(VI)nonavanadate(V) ([Mo^VIV₉O₂₈]^5-,V₉Mo) were investigated against the growth of Mycobacterium smegmatis with the EC₅₀ values of 0.0048 mM and 0.015 mM, respectively. These compare to the reported inhibitory value for decavanadate ([V₁₀O₂₈]^6-/[HV₁₀O₂₈]^5-, V₁₀) on Mycobacterium smegmatis (EC₅₀ = 0.0037 mM). Time-dependent ⁵¹V NMR spectroscopic studies were carried out for all three polyanions in aqueous solution, biological medium (7H9), heated and non-heated supernatant to evaluate their stability in their respective media, monitor their hydrolysis to form various oxovanadates over time and calculate the EC₅₀ values. These studies allow us to calculate adjusted and maximum EC₅₀ for the polyoxovanadate (POV) present in solution at the beginning of the study when there is most intact anion in the media and thus the EC₅₀ values represent the initial effects of the POVs. The results have shown that V₁₀ is 1.3 times more potent than V₉Pt and 4 times more potent than V₉Mo, indicating that the inhibitory effects of monosubstituted polyanions are related to the V₁₀ structure. We attributed the minor differences in the growth inhibitory effects to the differences in charges (5- vs 6-) of V₉Pt and V₉Mo compared to V₁₀ and/or the differences in the chemical composition. We concluded that the potency of the growth inhibition by V₁₀ is mainly due to the chemical properties of the vanadium and the decametalate's unique structure even though the presence of the Mycobacterium smegmatis facilitate hydrolysis of the anions. SYNOPSIS: Two decavanadate derivatives, monoplatino(IV)nonavanadate(V) ([H₂Pt^IVV₉O₂₈]^5-), monomolybdo(VI)nonavanadate(V) ([Mo^VIV₉O₂₈]^5-) and decavanadate are more potent growth inhibitors of Mycobacterium smegmatis than monomeric vanadate. The spectroscopic characterization carried out in the growth medium led to the conclusion that both the decavanadate structure and its properties are important for its growth effects.

Multivalent ions and biomolecules: Attempting a comprehensive perspective

Ions are ubiquitous in nature. They play a key role for many biological processes on the molecular scale, from molecular interactions, to mechanical properties, to folding, to self-organisation and assembly, to reaction equilibria, to signalling, to energy and material transport, to recognition etc. Going beyond monovalent ions to multivalent ions, the effects of the ions are frequently not only stronger (due to the obviously higher charge), but qualitatively different. A typical example is the process of binding of multivalent ions, such as Ca2+ , to a macromolecule and the consequences of this ion binding such as compaction, collapse, potential charge inversion and precipitation of the macromolecule. Here we review these effects and phenomena induced by multivalent ions for biological (macro)molecules, from the "atomistic/molecular" local picture of (potentially specific) interactions to the more global picture of phase behaviour including, e. g., crystallisation, phase separation, oligomerisation etc. Rather than attempting an encyclopedic list of systems, we rather aim for an embracing discussion using typical case studies. We try to cover predominantly three main classes: proteins, nucleic acids, and amphiphilic molecules including interface effects. We do not cover in detail, but make some comparisons to, ion channels, colloidal systems, and synthetic polymers. While there are obvious differences in the behaviour of, and the relevance of multivalent ions for, the three main classes of systems, we also point out analogies. Our attempt of a comprehensive discussion is guided by the idea that there are not only important differences and specific phenomena with regard to the effects of multivalent ions on the main systems, but also important similarities. We hope to bridge physico-chemical mechanisms, concepts of soft matter, and biological observations and connect the different communities further.

In Vitro Anti-tumoral and Anti-bacterial Activity of an Octamolybdate Cluster-Based Hybrid Solid Incorporated with a Copper Picolinate Complex

Inorganic drugs, especially polyoxometalate-based hybrids, are expected to be developed as promising future metallodrugs. Herein, an organic-inorganic hybrid solid based on pyridine-2-carboxylic acid or picolinic acid (pic), [(Cu(pic)₂)₂(Mo₈O₂₆)]·8H₂O (1), was synthesized. A single-crystal structure of a solid possesses a discrete β-type octamolybdate cluster that supramolecularly aggregates with a {Cu₂(pic)₄}^4- complex and eight lattice water molecules. The study indicates that the solid is stable in aqueous medium and less toxic toward normal cell lines. The in vitro anti-bacterial and anti-tumor properties of the solid 1 were investigated. The results of the anti-tumor action against various human cancer cell lines, namely, lung (A549), breast (MCF-7), and liver (HepG2) cancer cells suggest that this β-octamolybdate-based solid yielded the lowest IC₅₀ value reported so far among octamolybdate anion-based hybrid solids, i.e., 24.24 μM for MCF-7, 21.56 μM for HepG2, and 25 μM for A549, indicating significant anti-cancer activity. The cell cycle analysis further reveals the observed anti-tumor effect to be governed by the arrest of breast cancer cells in the G2/M phase while that of lung and liver cancer cells in the S phase of the cell cycle. A fluorescence quenching study suggests the binding interaction between solid and ctDNA, which in turn induces apoptosis and necrosis pathways leading to cancer cell death. This is also the first study of {Mo₈O₂₆}^4- cluster-based solids as an anti-bacterial agent against Escherichia coli, and it was found to be very effective with a minimal inhibitory concentration value of ∼135 μg/mL, which is the lowest so far reported for any octamolybdate-based solid.

Structure-Activity Relationships for the Affinity of Chaotropic Polyoxometalate Anions towards Proteins

The influence of the composition of chaotropic polyoxometalate (POM) anions on their affinity to biological systems was studied by means of atomistic molecular dynamics (MD) simulations. The variations in the affinity to hen egg-white lysozyme (HEWL) were analyzed along two series of POMs whereby the charge or the size and shape of the metal cluster are modified systematically. Our simulations revealed a quadratic relationship between the charge of the POM and its affinity to HEWL as a consequence of the parabolic growth of POM⋅⋅⋅water interaction with the charge. As the charge increases, POMs become less chaotropic (more kosmotropic) increasing the number and the strength of POM-water hydrogen bonds and structuring the solvation shell around the POM. This atomistic description explains the proportionally larger desolvation energies and less protein affinity for highly charged POMs, and consequently, the preference for moderate charge densities (q/M=0.33). Also, our simulations suggest that POM⋅⋅⋅protein interactions are size-specific. The cationic pockets of HEWL protein show a preference for Keggin-like structures, which display the optimal dimensions (≈1 nm). Finally, we developed a quantitative multidimensional model for protein affinity with predictive ability (r² =0.97; q² =0.88) using two molecular descriptors that account for the charge density (charge per metal atom ratio; q/M) and the size and shape (shape weighted-volume; V_S ).

Polyoxometalates in Biomedicine: Update and Overview

BACKGROUND

Polyoxometalates (POMs) are negatively charged metal-oxo clusters of early transition metal ions in high oxidation states (e.g., WVI, MoVI, VV). POMs are of interest in the fields of catalysis, electronics, magnetic materials and nanotechnology. Moreover, POMs were shown to exhibit biological activities in vitro and in vivo, such as antitumor, antimicrobial, and antidiabetic.

METHODS

The literature search for this peer-reviewed article was performed using PubMed and Scopus databases with the help of appropriate keywords.

RESULTS

This review gives a comprehensive overview of recent studies regarding biological activities of polyoxometalates, and their biomedical applications as promising anti-viral, anti-bacterial, anti-tumor, and anti-diabetic agents. Additionally, their putative mechanisms of action and molecular targets are particularly considered.

CONCLUSION

Although a wide range of biological activities of Polyoxometalates (POMs) has been reported, they are to the best of our knowledge not close to a clinical trial or a final application in the treatment of diabetes or infectious and malignant diseases. Accordingly, further studies should be directed towards determining the mechanism of POM biological actions, which would enable fine-tuning at the molecular level, and consequently efficient action towards biological targets and as low toxicity as possible. Furthermore, biomedical studies should be performed on solutionstable POMs employing physiological conditions and concentrations.

Investigation of complexation of amlodipine with lysozyme and its effect on lysozyme crystal growth

Lysozyme (LYZ) is a model protein frequently employed to study interaction with drugs and to understand the crystallization process of protein due to its small size and rapid crystallization behavior. Studies related to drug interaction and complexation with proteins will be significantly benefited if a suitable drug-lysozyme crystal is available. This can further aid in the understanding of the mechanism of nucleation, growth and the formation of drug-lysozyme complex. In the present study, amlodipine (AMLD) complexation with LYZ has been monitored, along with its effect on lysozyme crystallization. Different spectroscopic methods have been employed to monitor the nature of complexation, binding mode and changes in helix after interaction with AMLD. The absorbance and fluorescence spectroscopic measurement indicated the probability of a ground state complex between LYZ and AMLD. Further, the temperature dependent fluorescence studies showed an increase in binding constant with temperature, suggesting the static quenching mechanism involved in complex formation due to hydrophobic interactions. CD, FTIR, DLS and DSC techniques confirm the probability of changes in the tertiary structure of protein. Molecular docking was applied to investigate the interaction of amino acid residues of LYZ with AMLD. It was found that the complex formation is spontaneous and the ΔG value obtained (-21. 76 kJ/mol) very well matched with temperature dependent fluorescence study (-24.91 kJ/mol). Crystallization of LYZ was performed with different concentration ranges of AMLD to get a clear picture of its interference on the process. The time required for crystallization of AMLD-LYZ complex and the observed structure of crystal indicates that AMLD influences lysozyme crystallization process by changing the nature of nucleation and rate of crystal growth.

Polyoxometalates in solution: speciation under spotlight

The review covers stability and transformations of classical polyoxometalates in aqueous solutions and provides their ion-distribution diagrams over a wide pH range.

Protein crystal structure determination with the crystallophore, a nucleating and phasing agent

Obtaining crystals and solving the phase problem remain major hurdles encountered by bio-crystallographers in their race to obtain new high-quality structures. Both issues can be overcome by the crystallophore, Tb-Xo4, a lanthanide-based molecular complex with unique nucleating and phasing properties. This article presents examples of new crystallization conditions induced by the presence of Tb-Xo4. These new crystalline forms bypass crystal defects often encountered by crystallographers, such as low-resolution diffracting samples or crystals with twinning. Thanks to Tb-Xo4's high phasing power, the structure determination process is greatly facilitated and can be extended to serial crystallography approaches.

Ionic liquids skeleton typed magnetic core-shell molecularly imprinted polymers for the specific recognition of lysozyme

The novel ionic liquids skeleton typed magnetic core-shell molecularly imprinted polymers (Fe₃O₄-COOH@IL-MIP) were firstly constructed with 1-vinyl-3-aminoformylmethyl imidazolium chloride ionic liquid ([VAFMIM]Cl-IL) modified magnetic particles as the substrate materials, [VAFMIM]Cl-IL as functional monomer, 1,6-hexanediyl-3,3'-bis-1-vinylimidazolium dichloride ionic liquid as cross-linker and Lysozyme (Lys) as template protein via surface-imprinting technique. The structure of Fe₃O₄-COOH@IL-MIP were confirmed by transmission and scanning electron microscopy, dynamic light scattering, thermo-gravimetric analysis, fourier transform infrared spectrometry and X-ray diffraction. The adsorption mechanism was discussed from the perspective of amino acid residues of Lys. The maximum adsorption capacity of MIPs was 166.36 mg g^-1 and imprinting factor was 2.67. The competitive adsorption experiments demonstrated the favorable recognition ability of MIPs toward Lys. Reusability studies indicated MIPs can be reused ten times without obvious loss of rebinding ability. The Lys conformation maintained intact after elution and the elution rate was as high as 74%. The adsorption experiment of egg white manifested that MIPs can effectively separate Lys in practical samples. Only ILs and Fe₃O₄ were utilized to fabricate MIPs, this strategy realized the goal of energy and cost saving while achieving simple synthesis of imprinted materials, and is expected to provide a new feasible idea to exploit synthetic methods for protein-MIPs.

Experimental and theoretical insights of functionalized hexavanadates on Na+/K+-ATPase activity; molecular interaction field, ab initio calculations and in vitro assays

The influence of three functionalized hexavanadates (V₆): Na₂ [V₆O₁₃{(OCH₂)₃CCH₃}₂], [H₂]₂ [V₆O₁₃{(OCH₂)₃CCH₂OCOCH₂CH₃}₂] and [(C₄H₉)₄N]₂ [V₆O₁₃{(OCH₂)₃CCH₂OOC(CH₃)₂-COOH}₂ on Na⁺/K⁺-ATPase activity, was investigated in vitro. Including compounds already tested by Xu et al. (Journal of Inorganic Biochemistry 161 (2016) 27-36), all functionalized hexavanadates inhibit the activity of Na⁺/K⁺-ATPase in a dose-dependent manner but with different inhibitory potencies. Na₂ [V₆O₁₃{(OCH₂)₃CCH₃}₂] was found to have the best inhibition properties - showing 50% inhibition IC₅₀ = 5.50 × 10^-5 M, while [(C₄H₉)₄N]₂ [V₆O₁₃{(OCH₂)₃CCH₂OOC(CH₃)₂-COOH}₂] showed the lowest inhibitory power, IC₅₀ = 1.31 × 10^-4 M. In order to understand the bioactivity of functionalized hexavanadates series, we have also used a combined theoretical approach: determination of electrostatic potential from ab initio theoretical calculations and computation of the molecular interaction field (MIF) surface.

Enhancement of Lysozyme Crystallization Using DNA as a Polymeric Additive

This study reports the first experimental evidence of using DNA as a polymeric additive to enhance protein crystallization. Using three kinds of DNA with different molecular weights—calf DNA, salmon DNA, and herring DNA—this study showed an improvement in the success rate of lysozyme crystallization, as compared to control experiments, especially at low lysozyme concentration. The improvement of crystallization is particularly significant in the presence of calf DNA with the highest molecular weight. Calf DNA also speeds up the induction time of lysozyme crystallization and increases the number of crystals per drop. We hypothesized the effect of DNA on protein crystallization may be due to the combination of excluded volume effect, change of water’s surface tension, and the water competition effect. This work confirms predications of the potential use of DNA as a polymeric additive to enhance protein crystallization, potentially applied to systems with limited protein available or difficult to crystallize.

Photoluminescence Properties of Two Closely Related Isostructural Series Based on Anderson-Evans Cluster Coordinated With Lanthanides [Ln(H2O)7{X(OH)6Mo6O18}]•yH2O, X = Al, Cr

The paper describes synthesis and structural characterization of the whole series of two closely related lanthanide coordinated chromium or aluminum hexamolybdates (Anderson-Evans cluster) including twelve new members hitherto unreported: [Ln(H₂O)₇{X(OH)₆Mo₆O₁₈}]·4H₂O and [Ln(H₂O)₇{X(OH)₆Mo₆O₁₈}Ln(H₂O)₇]{X(OH)₆Mo₆O₁₈}·16H₂O where X = Al or Cr and Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y. Crystal structures of all the solids were established by powder and single crystal X-ray diffraction techniques. The two series are dictated by a different aggregation of the same set of molecular species: Lighter lanthanides favor coordination interaction between lanthanide ions and molybdate cluster forming 1D chains (Series I) while the heavier lanthanides result in the stacking of a cation, a pair of lanthanide hydrates coordinating to the cluster, and an anion, the discrete cluster is further stabilized through a large number of water molecules (Series II). Crystallization with Er³⁺ and Tm³⁺ ions results in a concomitant mixture of Series I and II. Photoluminescence of single crystals of all the chromium molybdates was dominated by a ruby-like emission including those which contain optically active ions Pr, Sm, Eu, Tb, Dy, and Tm. In contrast, aluminum analogs showed photoluminescence corresponding to characteristic lanthanide emissions. Our results strongly suggest a possible energy transfer from f levels of lanthanide ions to d levels of chromium (III) causing the quenching of lanthanide emission when coordinated with chromium molybdates. Intensity measurements showed that the emission from chromium molybdates are almost two orders of magnitude lower than naturally occurring ruby with broader line widths at room temperature.

Interactions between polyoxometalates and biological systems: from drug design to artificial enzymes

Polyoxometalates have long been studied in a variety of biological applications. Interactions between the highly charged POM molecules and biological molecules frequently occur through hydrogen-bonding and electrostatic interactions. Tellurium-centred Anderson-Evans POMs show exceptional promise as crystallization agents, while acidic and metal-substituted POMs may provide interesting alternatives to enzymes in proteomics applications. While POMs also show interesting results in a number of medicinal applications, for example as anti-amyloid agents for the treatment of Alzheimer's disease and as anti-tumoral agents, their use is often impeded by their toxicity. Many recent studies have therefore focussed on POM-functionalization to reduce toxicity and increase activity by addition of biological targeting molecules.

The Chaotropic Effect as an Assembly Motif in Chemistry

Following up on scattered reports on interactions of conventional chaotropic ions (for example, I- , SCN- , ClO4- ) with macrocyclic host molecules, biomolecules, and hydrophobic neutral surfaces in aqueous solution, the chaotropic effect has recently emerged as a generic driving force for supramolecular assembly, orthogonal to the hydrophobic effect. The chaotropic effect becomes most effective for very large ions that extend beyond the classical Hofmeister scale and that can be referred to as superchaotropic ions (for example, borate clusters and polyoxometalates). In this Minireview, we present a continuous scale of water-solute interactions that includes the solvation of kosmotropic, chaotropic, and hydrophobic solutes, as well as the creation of void space (cavitation). Recent examples for the association of chaotropic anions to hydrophobic synthetic and biological binding sites, lipid bilayers, and surfaces are discussed.

What is new in lysozyme research and its application in food industry? A review

Lysozyme, an important bacteriostatic protein, is widely distributed in nature. It is generally believed that the high efficiency of lysozyme in inhibiting gram-positive bacteria is caused by its ability to cleave the β-(1,4)-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine. In recent years, there has been growing interest in modifying lysozyme via physical or chemical interactions in order to improve its sensitivity against gram-negative bacterial strains. This review addresses some significant techniques, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), infrared (IR) spectra, fluorescence spectroscopy, nuclear magnetic resonance (NMR), UV-vis spectroscopy, circular dichroism (CD) spectra and differential scanning calorimetry (DSC), which can be used to characterize lysozymes and methods that modify lysozymes with carbohydrates to enhance their various physicochemical characteristics. The applications of biomaterials based on lysozymes in different food matrices are also discussed.

Polyoxometalates: more than a phasing tool in protein crystallography

Protein crystallography is the most widely used method for determining the molecular structure of proteins and obtaining structural information on protein–ligand complexes at the atomic level. As the structure determines the functions and properties of a protein, crystallography is of immense importance for nearly all research fields related to biochemistry. However, protein crystallography suffers from some major drawbacks, whereby the unpredictability of the crystallization process represents the main bottleneck. Crystallization is still more or less a ‘trial and error’ based procedure, and therefore, very time and resource consuming. Many strategies  have been developed in the past decades to improve or enable the crystallization of proteins, whereby the use of so-called additives, which are mostly small molecules that make proteins more amenable to crystallization, is one of the most convenient and successful methods. Most of the commonly used additives are, however, restricted to particular crystallization conditions or groups of proteins. Therefore, a more universal additive addressing a wider range of proteins and being applicable to a broad spectrum of crystallization conditions would represent a significant advance in the field of protein crystallography. In recent years, polyoxometalates (POMs) emerged as a promising group of crystallization additives due to their unique structures and properties. In this regard, the tellurium-centered Anderson–Evans polyoxotungstate [TeW₆O₂₄]⁶⁻ (TEW) showed its high potential as crystallization additive. In this lecture text, the development of POMs as tools in protein crystallography are discussed with a special focus on the so far most successful cluster TEW.

Principles and methods used to grow and optimize crystals of protein-metallodrug adducts, to determine metal binding sites and to assign metal ligands

The characterization of the interactions between biological macromolecules (proteins and nucleic acids) and metal-based drugs is a fundamental prerequisite for understanding their mechanisms of action. X-ray crystallography enables the structural analysis of such complexes with atomic level detail. However, this approach requires the preparation of highly diffracting single crystals, the measurement of diffraction patterns and the structural analysis and interpretation of macromolecule-metal interactions from electron density maps. In this review, we describe principles and methods used to grow and optimize crystals of protein-metallodrug adducts, to determine metal binding sites and to assign and validate metal ligands. Examples from the literature and experience in our own laboratory are provided and key challenges are described, notably crystallization and molecular model refinement against the X-ray diffraction data.

The crystallization additive hexatungstotellurate promotes the crystallization of the HSP70 nucleotide binding domain into two different crystal forms

The use of the tellurium-centered Anderson-Evans polyoxotungstate [TeW6O24]6- (TEW) as a crystallization additive has been described. Here, we present the use of TEW as an additive in the crystallization screening of the nucleotide binding domain (NBD) of HSP70. Crystallization screening of the HSP70 NBD in the absence of TEW using a standard commercial screen resulted in a single crystal form. An identical crystallization screen of the HSP70 NBD in the presence of TEW resulted in both the "TEW free" crystal form and an additional crystal form with a different crystal packing. TEW binding was observed in both crystal forms, either as a well-defined molecule or in overlapping alternate positions suggesting translational disorder. The structures were solved by both molecular replacement and single wavelength anomalous diffraction (SAD) using the anomalous signal of a single bound molecule of TEW. This study adds one more example of TEW binding to a protein and influencing its crystallization behavior.

The P-type ATPase inhibiting potential of polyoxotungstates

Polyoxometalates (POMs) are transition metal complexes that exhibit a broad diversity of structures and properties rendering them promising for biological purposes. POMs are able to inhibit a series of biologically important enzymes, including phosphatases, and thus are able to affect many biochemical processes. In the present study, we analyzed and compared the inhibitory effects of nine different polyoxotungstates (POTs) on two P-type ATPases, Ca2+-ATPase from skeletal muscle and Na+/K+-ATPase from basal membrane of skin epithelia. For Ca2+-ATPase inhibition, an in vitro study was performed and the strongest inhibitors were determined to be the large heteropolytungstate K9(C2H8N)5[H10Se2W29O103] (Se2W29) and the Dawson-type POT K6[α-P2W18O62] (P2W18) exhibiting IC50 values of 0.3 and 0.6 μM, respectively. Promising results were also shown for the Keggin-based POTs K6H2[CoW11TiO40] (CoW11Ti, IC50 = 4 μM) and Na10[α-SiW9O34] (SiW9, IC50 = 16 μM), K14[As2W19O67(H2O)] (As2W19, IC50 = 28 μM) and the lacunary Dawson K12[α-H2P2W12O48] (P2W12, IC50 = 11 μM), whereas low inhibitory potencies were observed for the isopolytungstate Na12[H4W22O74] (W22, IC50 = 68 μM) and the Anderson-type Na6[TeW6O24] (TeW6, IC50 = 200 μM). Regarding the inhibition of Na+/K+-ATPase activity, for the first time an ex vivo study was conducted using the opercular epithelium of killifish in order to investigate the effects of POTs on the epithelial chloride secretion. Interestingly, 1 μM of the most potent Ca2+-ATPase inhibitor, Se2W29, showed only a minor inhibitory effect (14% inhibition) on Na+/K+-ATPase activity, whereas almost total inhibition (99% inhibition) was achieved using P2W18. The remaining POTs exhibited similar inhibition rates on both ATPases. These results reveal the high potential of some POTs to act as P-type ATPase inhibitors, with Se2W29 showing high selectivity towards Ca2+-ATPase.

The antibacterial activity of polyoxometalates: structures, antibiotic effects and future perspectives

Polyoxometalates (POMs) are, mostly anionic, metal oxide compounds that span a wide range of tunable physical and chemical features rendering them very interesting for biological purposes, an continuously emerging but little explored field. Due to their biological and biochemical effects, including antitumor, -viral and -bacterial properties, POMs and POM-based systems are considered as promising future metallodrugs. In this article, we focus on the antibacterial activity of POMs and their therapeutic potential in the battle against bacteria and their increasing resistance against pharmaceuticals. Recent advances in the synthesis of POMs are highlighted, with emphasis on the development and properties of biologically active POM-based hybrid and nanocomposite structures. By analysing the antibacterial activity and structure of POMs, putative mode of actions are provided, including potential targets for POM-protein interactions, and a structure-activity-relationship was established for a series of POMs against two bacteria, namely Helicobacter pylori and Streptococcus pneumoniae.

The potential of hexatungstotellurate(VI) to induce a significant entropic gain during protein crystallization

The limiting factor in protein crystallography is still the production of high-quality crystals. In this regard, the authors have recently introduced hexatungstotellurate(VI) (TEW) as a new crystallization additive, which proved to be successful within the liquid-liquid phase separation (LLPS) zone. Presented here are comparative crystal structure analyses revealing that protein-TEW binding not only induces and stabilizes crystal contacts, but also exhibits a significant impact on the solvent-driven crystallization entropy, which is the driving force for the crystallization process. Upon the formation of TEW-mediated protein-protein contacts, the release of water molecules from the hydration shells of both molecules, i.e. TEW and the protein, causes a reduced solvent-accessible surface area, leading to a significant gain in solvent entropy. Based on the crystal structures of aurone synthase (in the presence and absence of TEW), insights have also been provided into the formation of a metastable LLPS, which is caused by the formation of protein clusters, representing an ideal starting point in protein crystallization. The results strongly encourage the classification of TEW as a valuable crystallization additive.

Ten Good Reasons for the Use of the Tellurium-Centered Anderson-Evans Polyoxotungstate in Protein Crystallography

Protein crystallography represents at present the most productive and most widely used method to obtain structural information on target proteins and protein-ligand complexes within the atomic resolution range. The knowledge obtained in this way is essential for understanding the biology, chemistry, and biochemistry of proteins and their functions but also for the development of compounds of high pharmacological and medicinal interest. Here, we address the very central problem in protein crystallography: the unpredictability of the crystallization process. Obtaining protein crystals that diffract to high resolutions represents the essential step to perform any structural study by X-ray crystallography; however, this method still depends basically on trial and error making it a very time- and resource-consuming process. The use of additives is an established process to enable or improve the crystallization of proteins in order to obtain high quality crystals. Therefore, a more universal additive addressing a wider range of proteins is desirable as it would represent a huge advance in protein crystallography and at the same time drastically impact multiple research fields. This in turn could add an overall benefit for the entire society as it profits from the faster development of novel or improved drugs and from a deeper understanding of biological, biochemical, and pharmacological phenomena. With this aim in view, we have tested several compounds belonging to the emerging class of polyoxometalates (POMs) for their suitability as crystallization additives and revealed that the tellurium-centered Anderson-Evans polyoxotungstate [TeW6O24]6- (TEW) was the most suitable POM-archetype. After its first successful application as a crystallization additive, we repeatedly reported on TEW's positive effects on the crystallization behavior of proteins with a particular focus on the protein-TEW interactions. As electrostatic interactions are the main force for TEW binding to proteins, TEW with its highly negative charge addresses in principle all proteins possessing positively charged patches. Furthermore, due to its high structural and chemical diversity, TEW exhibits major advantages over some commonly used crystallization additives. Therefore, we summarized all features of TEW, which are beneficial for protein crystallization, and present ten good reasons to promote the use of TEW in protein crystallography as a powerful additive. Our results demonstrate that TEW is a compound that is, in many respects, predestined as a crystallization additive. We assume that many crystallographers and especially researchers, who are not experts in this field but willing to crystallize their structurally unknown target protein, could benefit from the use of TEW as it is able to promote both the crystallization process itself and the subsequent structure elucidation by providing valuable anomalous signals, which are helpful for the phasing step.

The "Sticky Patch" Model of Crystallization and Modification of Proteins for Enhanced Crystallizability

Crystallization of macromolecules has long been perceived as a stochastic process, which cannot be predicted or controlled. This is consistent with another popular notion that the interactions of molecules within the crystal, i.e., crystal contacts, are essentially random and devoid of specific physicochemical features. In contrast, functionally relevant surfaces, such as oligomerization interfaces and specific protein-protein interaction sites, are under evolutionary pressures so their amino acid composition, structure, and topology are distinct. However, current theoretical and experimental studies are significantly changing our understanding of the nature of crystallization. The increasingly popular "sticky patch" model, derived from soft matter physics, describes crystallization as a process driven by interactions between select, specific surface patches, with properties thermodynamically favorable for cohesive interactions. Independent support for this model comes from various sources including structural studies and bioinformatics. Proteins that are recalcitrant to crystallization can be modified for enhanced crystallizability through chemical or mutational modification of their surface to effectively engineer "sticky patches" which would drive crystallization. Here, we discuss the current state of knowledge of the relationship between the microscopic properties of the target macromolecule and its crystallizability, focusing on the "sticky patch" model. We discuss state-of-the-art in silico methods that evaluate the propensity of a given target protein to form crystals based on these relationships, with the objective to design variants with modified molecular surface properties and enhanced crystallization propensity. We illustrate this discussion with specific cases where these approaches allowed to generate crystals suitable for structural analysis.

A survey of the different roles of polyoxometalates in their interaction with amino acids, peptides and proteins

This perspective provides a comprehensive description of the different roles of POMs in their interaction with relevant biological molecules.

In situ formation of the first proteinogenically functionalized [TeW6O24O2(Glu)]7- structure reveals unprecedented chemical and geometrical features of the Anderson-type cluster

The chemistry of polyoxometalates (POMs) in a protein environment is an almost unexplored but highly relevant research field as important biological and pharmacological attributes of certain POMs are based on their interactions with proteins. We report on the A-type Anderson-Evans polyoxotungstate, [TeW6O24]6- (TEW), mediated crystallization of Coreopsis grandiflora aurone synthase (cgAUS1) using ∼0.24 mM protein and 1.0 mM TEW. The 1.78 Å crystal structure reveals the covalent binding of TEW to the protein under the formation of an unprecedented polyoxotungstate cluster, [TeW6O24O2(Glu)]7- (GluTEW). The polyoxotungstate-protein complex exhibits the first covalent bond between a protein and the A-type Anderson-Evans cluster, an archetype where up to now no hybrid structures exist. The polyoxotungstate is modified at two of its six addenda tungsten atoms, which covalently bind to the carboxylic oxygen atoms of glutamic acid (Glu157), leading to W-O distances of ∼2.35 Å. This ligand substitution reaction is accompanied by a reduction of the coordination number of two μ3 polyoxotungstate oxygen atoms. This is so far unique since all known hybridizations of the Anderson-Evans POM with organic units have been obtained via the functionalization of the B-type Anderson-Evans structure through its bridging oxygen atoms. The structure reported here proves the reactivity of this POM archetype's addenda atoms as it has been administered into the protein solution as a pre-assembled cluster. Moreover, the novel cluster [TeW6O24O2(Glu)]7- displays the great versatility of the Anderson-Evans POM class.

[Ni(OH)3W6O18(OCH2)3CCH2OH](4-): the first tris-functionalized Anderson-type heteropolytungstate

Na₂[TMA]₂[Ni(OH)₃W₆O₁₈(OCH₂)₃CCH₂OH]·9H₂O represents the first covalent tris-functionalized Anderson-type heteropolytungstate and was characterized by single-crystal X-ray diffraction, electrospray ionization mass spectrometry, TGA and IR spectroscopy.

Na₂[TMA]₂[Ni(OH)₃W₆O₁₈(OCH₂)₃CCH₂OH]·9H₂O represents the first covalent tris-functionalized Anderson-type heteropolytungstate and was characterized by single-crystal X-ray diffraction, electrospray ionization mass spectrometry, TGA and IR spectroscopy. Zeta potential measurements in solutions containing human serum albumin were performed to investigate electrostatic interactions with [Ni(OH)₃W₆O₁₈(OCH₂)₃CCH₂OH]^4–.

The proton-controlled synthesis of unprecedented diol functionalized Anderson-type POMs

By addition of excess acid into the reaction mixture, a series of organically-derived Anderson-type polyoxometalates, {[R1CR2(CH2O)2]CrMo6O18(OH)4}(3-), with diols as the ligands are reported herein. Such a diol functionalization mode not only works for some specific triol ligands but also can readily be extended to the diol ligands, which will greatly enrich the species of alkoxo-derivatized Anderson POM clusters.

Aurone synthase is a catechol oxidase with hydroxylase activity and provides insights into the mechanism of plant polyphenol oxidases

Tyrosinases and catechol oxidases belong to the family of polyphenol oxidases (PPOs). Tyrosinases catalyze theo-hydroxylation and oxidation of phenolic compounds, whereas catechol oxidases were so far defined to lack the hydroxylation activity and catalyze solely the oxidation of o-diphenolic compounds. Aurone synthase from Coreopsis grandiflora (AUS1) is a specialized plant PPO involved in the anabolic pathway of aurones. We present, to our knowledge, the first crystal structures of a latent plant PPO, its mature active and inactive form, caused by a sulfation of a copper binding histidine. Analysis of the latent proenzyme's interface between the shielding C-terminal domain and the main core provides insights into its activation mechanisms. As AUS1 did not accept common tyrosinase substrates (tyrosine and tyramine), the enzyme is classified as a catechol oxidase. However, AUS1 showed hydroxylase activity toward its natural substrate (isoliquiritigenin), revealing that the hydroxylase activity is not correlated with the acceptance of common tyrosinase substrates. Therefore, we propose that the hydroxylase reaction is a general functionality of PPOs. Molecular dynamics simulations of docked substrate-enzyme complexes were performed, and a key residue was identified that influences the plant PPO's acceptance or rejection of tyramine. Based on the evidenced hydroxylase activity and the interactions of specific residues with the substrates during the molecular dynamics simulations, a novel catalytic reaction mechanism for plant PPOs is proposed. The presented results strongly suggest that the physiological role of plant catechol oxidases were previously underestimated, as they might hydroxylate their--so far unknown--natural substrates in vivo.

Unprecedented χ isomers of single-side triol-functionalized Anderson polyoxometalates and their proton-controlled isomer transformation

The μ2-O atom in Anderson polyoxometalates was regioselectively activated by the introduction of protons, which, upon functionalization with triol ligands, could afford a series of unique χ isomers of the organically-derived Anderson cluster {[RCC(CH2O)3]MMo6O18(OH)3}(3-). Herein proton-controlled isomer transformation between the δ and χ isomer was observed by using the fingerprint region in the IR spectra and (13)C NMR spectra.

Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals

Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions.