Structural chemistry and biology of manganese metalloenzymes

Bacterial Metallostasis: Metal Sensing, Metalloproteome Remodeling, and Metal Trafficking

Transition metals function as structural and catalytic cofactors for a large diversity of proteins and enzymes that collectively comprise the metalloproteome. Metallostasis considers all cellular processes, notably metal sensing, metalloproteome remodeling, and trafficking (or allocation) of metals that collectively ensure the functional integrity and adaptability of the metalloproteome. Bacteria employ both protein and RNA-based mechanisms that sense intracellular transition metal bioavailability and orchestrate systems-level outputs that maintain metallostasis. In this review, we contextualize metallostasis by briefly discussing the metalloproteome and specialized roles that metals play in biology. We then offer a comprehensive perspective on the diversity of metalloregulatory proteins and metal-sensing riboswitches, defining general principles within each sensor superfamily that capture how specificity is encoded in the sequence, and how selectivity can be leveraged in downstream synthetic biology and biotechnology applications. This is followed by a discussion of recent work that highlights selected metalloregulatory outputs, including metalloproteome remodeling and metal allocation by metallochaperones to both client proteins and compartments. We close by briefly discussing places where more work is needed to fill in gaps in our understanding of metallostasis.

Manganese matere bonds in biological systems: PDB inspection and DFT calculations

A Protein Data Bank (PDB) survey has revealed noncovalent contacts involving Mn centres and protein residues. Their geometrical features are in line with the interaction between low electron density sites located along the Mn-O/N coordination bonds (σ-holes) and the lone pairs belonging to TYR, SER or HIS residues, known as a matere bond (MaB). Calculations at the PBE0-D3/def2-TZVP level of theory were used to investigate the strength and shed light on the physical nature of the interaction. We expect the results presented herein will be useful for those scientists working in the fields of bioinorganic chemistry, particulary in protein-metal docking, by providing new insights into transition metal⋯Lewis base interactions as well as a retrospective point of view to further understand the structural and functional implications of this key transition metal ion.

Interaction and competition for intestinal absorption by zinc, iron, copper, and manganese at the intestinal mucus layer

Trace elements such as zinc, manganese, copper, or iron are essential for a wide range of physiological functions. It is therefore crucial to ensure an adequate supply of these elements to the body. Many previous investigations have dealt with the role of transport proteins, in particular their selectivity for, and competition between, different ions. Another so far less well investigated major factor influencing the absorption of trace elements seems to be the intestinal mucus layer. This gel-like substance covers the entire gastrointestinal tract and its physiochemical properties can be mainly assigned to the glycoproteins it contains, so-called mucins. Interaction with mucins has already been demonstrated for some metals. However, knowledge about the impact on the respective bioavailability and competition between those metals is still sketchy. This review therefore aims to summarize the findings and knowledge gaps about potential effects regarding the interaction between gastrointestinal mucins and the trace elements iron, zinc, manganese, and copper. Mucins play an indispensable role in the absorption of these trace elements in the neutral to slightly alkaline environment of the intestine, by keeping them in a soluble form that can be absorbed by enterocytes. Furthermore, the studies so far indicate that the competition between these trace elements for uptake already starts at the intestinal mucus layer, yet further research is required to completely understand this interaction.

Ultrastructural Organization and Metal Elemental Composition of the Mandibles in Two Ladybird Species

The mandibles are among the most important appendages of insects' mouthparts. Their morpho-functional organization is correlated with the variation in dietary preferences. In this study, we investigated the ultrastructural organization and metal composition of the mandibles of two ladybird species with different dietary habits: Harmonia axyridis (an entomophagous species) and Subcoccinella vigintiquatuorpunctata (a phytophagous species). The ultrastructural organization was studied using Scanning and Transmission Electron Microscopy, whereas the metal composition was investigated using Energy-Dispersive X-ray spectroscopy (EDX). Significant differences were observed in the general organization and metal enrichment pattern between the two species. The mandibles of H. axyridis are large and present a molar part with two teeth, with the apical one showing a bifid apex. In contrast, S. vigintiquatuorpunctata exhibited a molar region with several teeth on its apical part. The study revealed significant differences in metal content between the teeth and the prostheca of H. axyridis. Mn was the most abundant element in teeth, whereas Cl was more abundant in the prostheca. In the case of S. vigintiquatuorpunctata, Si was the most abundant element in the prostheca, while Mn was more present in the teeth. A comparison between the two species revealed that both teeth and prostheca showed significant variation in the elemental composition. These findings underscore the role of dietary preferences in shaping the structural and metal composition variations in the mandibles of these two ladybird species.

A database overview of metal-coordination distances in metalloproteins

Metalloproteins are ubiquitous in all living organisms and take part in a very wide range of biological processes. For this reason, their experimental characterization is crucial to obtain improved knowledge of their structure and biological functions. The three-dimensional structure represents highly relevant information since it provides insight into the interaction between the metal ion(s) and the protein fold. Such interactions determine the chemical reactivity of the bound metal. The available PDB structures can contain errors due to experimental factors such as poor resolution and radiation damage. A lack of use of distance restraints during the refinement and validation process also impacts the structure quality. Here, the aim was to obtain a thorough overview of the distribution of the distances between metal ions and their donor atoms through the statistical analysis of a data set based on more than 115 000 metal-binding sites in proteins. This analysis not only produced reference data that can be used by experimentalists to support the structure-determination process, for example as refinement restraints, but also resulted in an improved insight into how protein coordination occurs for different metals and the nature of their binding interactions. In particular, the features of carboxylate coordination were inspected, which is the only type of interaction that is commonly present for nearly all metals.

Comparative Material and Mechanical Properties among Cicada Mouthparts: Cuticle Enhanced with Inorganic Elements Facilitates Piercing through Woody Stems for Feeding

Adult cicadas pierce woody stems with their mouthparts to feed on xylem, suggesting the presence of cuticular adaptations that could increase hardness and elastic modulus. We tested the following hypotheses: (a) the mouthpart cuticle includes inorganic elements, which augment the mechanical properties; (b) these elements are abundant in specific mouthpart structures and regions responsible for piercing wood; (c) there are correlations among elements, which could provide insights into patterns of element colocalization. We used scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to investigate mouthpart morphology and quantify the elemental composition of the cuticle among four cicada species, including periodical cicadas (Magicicada sp.). Nanoindentation was used to quantify hardness and elastic modulus of the mandibles. We found 12 inorganic elements, including colocalized manganese and zinc in the distal regions of the mandible, the structure most responsible for piercing through wood; nanoindentation determined that these regions were also significantly harder and had higher elastic modulus than other regions. Manganese and zinc abundance relates to increased hardness and stiffness as in the cuticle of other invertebrates; however, this is one of the first reports of cuticular metals among insects with piercing-sucking mouthparts (>100,000 described species). The present investigation provides insight into the feeding mechanism of cicadas, an important but understudied component of their life traits.

Structural insights into the elevator-type transport mechanism of a bacterial ZIP metal transporter

The Zrt-/Irt-like protein (ZIP) family consists of ubiquitously expressed divalent metal transporters critically involved in maintaining systemic and cellular homeostasis of zinc, iron, and manganese. Here, we present a study on a prokaryotic ZIP from Bordetella bronchiseptica (BbZIP) by combining structural biology, evolutionary covariance, computational modeling, and a variety of biochemical assays to tackle the issue of the transport mechanism which has not been established for the ZIP family. The apo state structure in an inward-facing conformation revealed a disassembled transport site, altered inter-helical interactions, and importantly, a rigid body movement of a 4-transmembrane helix (TM) bundle relative to the other TMs. The computationally generated and biochemically validated outward-facing conformation model revealed a slide of the 4-TM bundle, which carries the transport site(s), by approximately 8 Å toward the extracellular side against the static TMs which mediate dimerization. These findings allow us to conclude that BbZIP is an elevator-type transporter.

Manganese-catalyzed hydrogenation, dehydrogenation, and hydroelementation reactions

The emerging field of organometallic catalysis has shifted towards research on Earth-abundant transition metals due to their ready availability, economic advantage, and novel properties. In this case, manganese, the third most abundant transition-metal in the Earth's crust, has emerged as one of the leading competitors. Accordingly, a large number of molecularly-defined Mn-complexes has been synthesized and employed for hydrogenation, dehydrogenation, and hydroelementation reactions. In this regard, catalyst design is based on three pillars, namely, metal-ligand bifunctionality, ligand hemilability, and redox activity. Indeed, the developed catalysts not only differ in the number of chelating atoms they possess but also their working principles, thereby leading to different turnover numbers for product molecules. Hence, the critical assessment of molecularly defined manganese catalysts in terms of chelating atoms, reaction conditions, mechanistic pathway, and product turnover number is significant. Herein, we analyze manganese complexes for their catalytic activity, versatility to allow multiple transformations and their routes to convert substrates to target molecules. This article will also be helpful to get significant insight into ligand design, thereby aiding catalysis design.

From manganese oxidation to water oxidation: assembly and evolution of the water-splitting complex in photosystem II

The manganese cluster of photosystem II has been the focus of intense research aiming to understand the mechanism of H₂O-oxidation. Great effort has also been applied to investigating its oxidative photoassembly process, termed photoactivation that involves the light-driven incorporation of metal ions into the active Mn₄CaO₅ cluster. The knowledge gained on these topics has fundamental scientific significance, but may also provide the blueprints for the development of biomimetic devices capable of splitting water for solar energy applications. Accordingly, synthetic chemical approaches inspired by the native Mn cluster are actively being explored, for which the native catalyst is a useful benchmark. For both the natural and artificial catalysts, the assembly process of incorporating Mn ions into catalytically active Mn oxide complexes is an oxidative process. In both cases this process appears to share certain chemical features, such as producing an optimal fraction of open coordination sites on the metals to facilitate the binding of substrate water, as well as the involvement of alkali metals (e.g., Ca²⁺) to facilitate assembly and activate water-splitting catalysis. This review discusses the structure and formation of the metal cluster of the PSII H₂O-oxidizing complex in the context of what is known about the formation and chemical properties of different Mn oxides. Additionally, the evolutionary origin of the Mn₄CaO₅ is considered in light of hypotheses that soluble Mn²⁺ was an ancient source of reductant for some early photosynthetic reaction centers ('photomanganotrophy'), and recent evidence that PSII can form Mn oxides with structural resemblance to the geologically abundant birnessite class of minerals. A new functional role for Ca²⁺ to facilitate sustained Mn²⁺ oxidation during photomanganotrophy is proposed, which may explain proposed physiological intermediates during the likely evolutionary transition from anoxygenic to oxygenic photosynthesis.

Exceptional Manganese(II) Stability and Manganese(II)/Zinc(II) Selectivity with Rigid Polydentate Ligands

While MnII complexes meet increasing interest in biomedical applications, ligands are lacking that enable high MnII complex stability and selectivity vs. ZnII , the most relevant biological competitor. We report here two new bispidine derivatives, which provide rigid and large coordination cavities that perfectly match the size of MnII , yielding eight-coordinate MnII complexes with record stabilities. In contrast, the smaller ZnII ion cannot accommodate all ligand donors, resulting in highly strained and less stable six-coordinate complexes. Combined theoretical and experimental data (X-ray crystallography, potentiometry, relaxometry and 1 H NMR spectroscopy) demonstrate unprecedented selectivity for MnII vs. ZnII (KMnL /KZnL of 108 -1010 ), in sharp contrast to the usual Irving-Williams behavior, and record MnII complex stabilities and inertness with logKMnL close to 25.

Manganese transport in mammals by zinc transporter family proteins, ZNT and ZIP

Manganese (Mn) is an essential trace element required for various biological processes. However, excess Mn causes serious side effects in humans, including parkinsonism. Thus, elucidation of Mn homeostasis at the systemic, cellular, and molecular levels is important. Many metal transporters and channels can be involved in the transport and homeostasis of Mn, and an increasing body of evidence shows that several zinc (Zn) transporters belonging to the ZIP and ZNT families, specifically, ZNT10, ZIP8, and ZIP14, play pivotal roles in Mn metabolism. Mutations in the genes encoding these transporter proteins are associated with congenital disorders related to dysregulated Mn homeostasis in humans. Moreover, single nucleotide polymorphisms of ZIP8 are associated with multiple clinical phenotypes. In this review, we discuss the recent literature on the structural and biochemical features of ZNT10, ZIP8, and ZIP14, including transport mechanisms, regulation of expression, and pathophysiological functions. Because a disturbance in Mn homeostasis is closely associated with a variety of phenotypes and risk of human diseases, these transporters constitute a significant target for drug development. An understanding of the roles of these key transporters in Mn metabolism should provide new insights into pharmacological applications of their inhibitors and enhancers in human diseases.

Advancements in multifunctional manganese complexes for catalytic hydrogen transfer reactions

Catalytic hydrogen transfer reactions have enormous academic and industrial applications for the production of diverse molecular scaffolds. Over the past few decades, precious late transition-metal catalysts were employed for these reactions. The early transition metals have recently gained much attention due to their lower cost, less toxicity, and overall sustainability. In this regard, manganese, which is the third most abundant transition metal in the Earth's crust, has emerged as a viable alternative. However, the key to the success of such manganese-based complexes lies in the multifunctional ligand design and choice of appropriate ancillary ligands, which helps them mimic and, even in some cases, supersede noble metals' activities. The metal-ligand bifunctionality, achieved via deprotonation of the acidic C-H or N-H bonds, is one of the powerful strategies employed for this purpose. Alongside, the ligand hemilability in which a weakly chelating group tunes in between the coordinated and uncoordinated stages could effectively stabilize the reactive intermediates, thereby facilitating substrate activation and catalysis. Redox non-innocent ligands acting as an electron sink, thereby helping the metal center in steps gaining or losing electrons, and non-classical metal-ligand cooperativity has also played a significant role in the ligand design for manganese catalysis. The strategies were not only employed for the chemoselective hydrogenation of different reducible functionalities but also for the C-X (X = C/N) coupling reactions via HT and downstream cascade processes. This article features multifunctional ligand-based manganese complexes, highlighting the importance of ligand design and choice of ancillary ligands for achieving the desired catalytic activity and selectivity for HT reactions. We have also discussed the detailed reaction pathways for metal complexes involving bifunctionality, hemilability, redox activity, and indirect metal-ligand cooperativity. The synthetic utilization of those complexes in different organic transformations has also been detailed.

Environmental pollution and diabetes mellitus

Diabetes mellitus (DM) is a chromic metabolic disease that affects a large segment of the population worldwide. Physical inactivity, poor nutrition, and genetic predisposition are main risk factors for disease development. In the last decade, it was clear to the scientific community that DM development is linked to a novel disease inducer that was later defined as diabetogenic factors of pollution and endocrine disrupting agents. Environmental pollution is exponentially increasing in uncontrolled manner in several countries. Environmental pollutants are of diverse nature and toxicities, including polyaromatic hydrocarbons (PAHs), pesticides, and heavy metals. In the current review, we shed light on the impact of each class of these pollutants and the underlined molecular mechanism of diabetes induction and biological toxicities. Finally, a brief overview about the connection between coronavirus disease 2019 and diabetes pandemics is presented.

The DNA transporter ComEC has metal-dependent nuclease activity that is important for natural transformation

In the process of natural transformation bacteria import extracellular DNA molecules for integration into their genome. One strand of the incoming DNA molecule is degraded, whereas the remaining strand is transported across the cytoplasmic membrane. The DNA transport channel is provided by the protein ComEC. Many ComEC proteins have an extracellular C-terminal domain (CTD) with homology to the metallo-β-lactamase fold. Here we show that this CTD binds Mn²⁺ ions and exhibits Mn²⁺ -dependent phosphodiesterase and nuclease activities. Inactivation of the enzymatic activity of the CTD severely inhibits natural transformation in Bacillus subtilis. These data suggest that the ComEC CTD is a nuclease responsible for degrading the nontransforming DNA strand during natural transformation and that this process is important for efficient DNA import.

The Biochemical Properties of Manganese in Plants

Manganese (Mn) is an essential micronutrient with many functional roles in plant metabolism. Manganese acts as an activator and co-factor of hundreds of metalloenzymes in plants. Because of its ability to readily change oxidation state in biological systems, Mn plays and important role in a broad range of enzyme-catalyzed reactions, including redox reactions, phosphorylation, decarboxylation, and hydrolysis. Manganese(II) is the prevalent oxidation state of Mn in plants and exhibits fast ligand exchange kinetics, which means that Mn can often be substituted by other metal ions, such as Mg(II), which has similar ion characteristics and requirements to the ligand environment of the metal binding sites. Knowledge of the molecular mechanisms catalyzed by Mn and regulation of Mn insertion into the active site of Mn-dependent enzymes, in the presence of other metals, is gradually evolving. This review presents an overview of the chemistry and biochemistry of Mn in plants, including an updated list of known Mn-dependent enzymes, together with enzymes where Mn has been shown to exchange with other metal ions. Furthermore, the current knowledge of the structure and functional role of the three most well characterized Mn-containing metalloenzymes in plants; the oxygen evolving complex of photosystem II, Mn superoxide dismutase, and oxalate oxidase is summarized.

Coordination Behavior of 1,4-Disubstituted Cyclen Endowed with Phosphonate, Phosphonate Monoethylester, and H-Phosphinate Pendant Arms

Three 1,4,7,10-tetraazacyclododecane-based ligands disubstituted in 1,4-positions with phosphonic acid, phosphonate monoethyl-ester, and H-phosphinic acid pendant arms, 1,4-H4do2p, 1,4-H2do2pOEt, and 1,4-H2Bn2do2pH, were synthesized and their coordination to selected metal ions, Mg(II), Ca(II), Mn(II), Zn(II), Cu(II), Eu(III), Gd(III), and Tb(III), was investigated. The solid-state structure of the phosphonate ligand, 1,4-H4do2p, was determined by single-crystal X-ray diffraction. Protonation constants of the ligands and stability constants of their complexes were obtained by potentiometry, and their values are comparable to those of previously studied analogous 1,7-disubstitued cyclen derivatives. The Gd(III) complex of 1,4-H4do2p is ~1 order of magnitude more stable than the Gd(III) complex of the 1,7-analogue, probably due to the disubstituted ethylenediamine-like structural motif in 1,4-H4do2p enabling more efficient wrapping of the metal ion. Stability of Gd(III)-1,4-H2do2pOEt and Gd(III)-H2Bn2do2pH complexes is low and the constants cannot be determined due to precipitation of the metal hydroxide. Protonations of the Cu(II), Zn(II), and Gd(III) complexes probably takes place on the coordinated phosphonate groups. Complexes of Mn(II) and alkali-earth metal ions are significantly less stable and are not formed in acidic solutions. Potential presence of water molecule(s) in the coordination spheres of the Mn(II) and Ln(III) complexes was studied by variable-temperature NMR experiments. The Mn(II) complexes of the ligands are not hydrated. The Gd(III)-1,4-H4do2p complex undergoes hydration equilibrium between mono- and bis-hydrated species. Presence of two-species equilibrium was confirmed by UV-Vis spectroscopy of the Eu(III)-1,4-H4do2p complex and hydration states were also determined by luminescence measurements of the Eu(III)/Tb(III)-1,4-H4do2p complexes.

Transcriptome Analysis Reveals Distinct Responses to Physiologic versus Toxic Manganese Exposure in Human Neuroblastoma Cells

Manganese (Mn) is an essential trace element, which also causes neurotoxicity in exposed occupational workers. Mn causes mitochondrial toxicity; however, little is known about transcriptional responses discriminated by physiological and toxicological levels of Mn. Identification of such mechanisms could provide means to evaluate risk of Mn toxicity and also potential avenues to protect against adverse effects. To study the Mn dose-response effects on transcription, analyzed by RNA-Seq, we used human SH-SY5Y neuroblastoma cells exposed for 5 h to Mn (0 to 100 μM), a time point where no immediate cell death occurred at any of the doses. Results showed widespread effects on abundance of protein-coding genes for metabolism of reactive oxygen species, energy sensing, glycolysis, and protein homeostasis including the unfolded protein response and transcriptional regulation. Exposure to a concentration (10 μM Mn for 5 h) that did not result in cell death after 24-h increased abundance of differentially expressed genes (DEGs) in the protein secretion pathway that function in protein trafficking and cellular homeostasis. These include BET1 (Golgi vesicular membrane-trafficking protein), ADAM10 (ADAM metallopeptidase domain 10), and ARFGAP3 (ADP-ribosylation factor GTPase-activating protein 3). In contrast, 5-h exposure to 100 μM Mn, a concentration that caused cell death after 24 h, increased abundance of DEGs for components of the mitochondrial oxidative phosphorylation pathway. Integrated pathway analysis results showed that protein secretion gene set was associated with amino acid metabolites in response to 10 μM Mn, while oxidative phosphorylation gene set was associated with energy, lipid, and neurotransmitter metabolites at 100 μM Mn. These results show that differential effects of Mn occur at a concentration which does not cause subsequent cell death compared to a concentration that causes subsequent cell death. If these responses translate to effects on the secretory pathway and mitochondrial functions in vivo, differential activities of these systems could provide a sensitive basis to discriminate sub-toxic and toxic environmental and occupational Mn exposures.

Formation of Unstable and very Reactive Chemical Species Catalyzed by Metalloenzymes: A Mechanistic Overview

Nature has tailored a wide range of metalloenzymes that play a vast array of functions in all living organisms and from which their survival and evolution depends on. These enzymes catalyze some of the most important biological processes in nature, such as photosynthesis, respiration, water oxidation, molecular oxygen reduction, and nitrogen fixation. They are also among the most proficient catalysts in terms of their activity, selectivity, and ability to operate at mild conditions of temperature, pH, and pressure. In the absence of these enzymes, these reactions would proceed very slowly, if at all, suggesting that these enzymes made the way for the emergence of life as we know today. In this review, the structure and catalytic mechanism of a selection of diverse metalloenzymes that are involved in the production of highly reactive and unstable species, such as hydroxide anions, hydrides, radical species, and superoxide molecules are analyzed. The formation of such reaction intermediates is very difficult to occur under biological conditions and only a rationalized selection of a particular metal ion, coordinated to a very specific group of ligands, and immersed in specific proteins allows these reactions to proceed. Interestingly, different metal coordination spheres can be used to produce the same reactive and unstable species, although through a different chemistry. A selection of hand-picked examples of different metalloenzymes illustrating this diversity is provided and the participation of different metal ions in similar reactions (but involving different mechanism) is discussed.

Modulating effect of tiron on the capability of mitochondrial oxidative phosphorylation in the brain of rats exposed to radiation or manganese toxicity

The brain is an important organ rich in mitochondria and more susceptible to oxidative stress. Tiron (sodium 4,5-dihydroxybenzene-1,3-disulfonate) is a potent antioxidant. This study aims to evaluate the effect of tiron on the impairment of brain mitochondria induced by exposure to radiation or manganese (Mn) toxicity. We assessed the capability of oxidative phosphorylation (OXPHOS) through determination of mitochondrial redox state, the activity of electron transport chain (ETC), and Krebs cycle as well as the level of adenosine triphosphate (ATP) production. Rats were exposed to 7 Gy of γ-rays or injected i.p. with manganese chloride (100 mg/kg), then treated with tiron (471 mg/kg) for 7 days. The results showed that tiron treatment revealed positive modulation on the mitochondrial redox state manifested by a marked decrease of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and total nitrate/nitrite (NO_x) associated with a significant increase in total antioxidant capacity (TAC), glutathione (GSH) content, manganese superoxide dismutase (MnSOD), and glutathione peroxidase (GPx) activities. Moreover, tiron can increase the activity of ETC through preventing the depletion in the activity of mitochondrial complexes (I, II, III, and IV), an elevation of coenzyme Q10 (CoQ10) and cytochrome c (Cyt-c) levels. Additionally, tiron showed a noticeable increase in mitochondrial aconitase (mt-aconitase) activity as the major component of Krebs cycle to maintain a high level of ATP production. Tiron also can restore mitochondrial metal homeostasis through positive changes in the levels of calcium (Ca), iron (Fe), Mn, and copper (Cu). It can be concluded that tiron may be used as a good mitigating agent to attenuate the harmful effects on the brain through the inhibition of mitochondrial injury post-exposure to radiation or Mn toxicity.

Trace elements effect on hydrolytic stage towards biogas production of model lignocellulosic substrates

The effect and the response of several trace elements (TE) addition to the anaerobic degradation of key compounds of lignocellulosic biomass were evaluated. Lignin, cellulose and xylose were selected as principal compounds of lignocellulosic biomass. Lignin degradation was only improved by the addition of 1000 mg Fe/L, which allowed an improvement on the methane yield coefficient of 28% compared to control. SEM images from an abiotic assay showed that this effect is more likely related with a chemical effect induced by the Fe solution, instead of an enzymatic response. Pre-treatments focused on breaking the recalcitrant structure of the lignin could be more promising than TE addition for rich lignin-content substrates. Unlike to the response observed with lignin, cellulose showed a clear effect of the TE addition on methane production rate, indicating a higher preponderance of the enzymatic activity compared to the lignin biomethanization. Experiments with xylose resulted in a strong accumulation of volatile fatty acids. TE addition should be adapted to the substrate composition given the different response of each lignocellulosic compound to the different TE addition.

Gene expression patterns indicate that a high-fat-high-carbohydrate diet causes mitochondrial dysfunction in fish

Expensive and unsustainable fishmeal is increasingly being replaced with cheaper lipids and carbohydrates as sources of energy in aquaculture. Although it is known that the excess of lipids and carbohydrates has negative effects on nutrient utilization, growth, metabolic homeostasis, and health of fish, our current understanding of mechanisms behind these effects is limited. To improve the understanding of diet-induced metabolic disorders (both in fish and other vertebrates), we conducted an eight-week high-fat-high-carbohydrate diet feeding trial on blunt snout bream (Megalobrama amblycephala), and studied gene expression changes (transcriptome and qPCR) in the liver. Disproportionately large numbers of differentially expressed genes were associated with mitochondrial metabolism, neurodegenerative diseases (Alzheimer's, Huntington's, and Parkinson's), and functional categories indicative of liver dysfunction. A high-fat-high-carbohydrate diet may have caused mitochondrial dysfunction, and possibly downregulated the mitochondrial biogenesis in the liver. While the relationship between diet and neurodegenerative disorders is well-established in mammals, this is the first report of this connection in fish. We propose that fishes should be further explored as a potentially promising model to study the mechanisms of diet-associated neurodegenerative disorders in humans.

Gold Nanoparticle-Based Photoluminescent Nanoswitch Controlled by Host-Guest Recognition and Enzymatic Hydrolysis for Arginase Activity Assay

The development of simple yet powerful methods for monitoring enzyme activity is of great significance. Herein, a facile, convenient, cost-effective, and continuous fluorescent method for the detection of arginase and its inhibitor has been reported based on a host-guest interaction-controlled and enzymatic hydrolysis-controlled luminescent nanoswitch. The fluorescence intensity of 6-aza-2-thiothymine-stabilized gold nanoparticle (ATT-AuNP) is enhanced by l-arginine, owing to the formation of a supramolecular host-guest assembly between the guanidine group of l-arginine and ATT molecules capped on the AuNP surface. However, hydrolysis of l-arginine, catalyzed by arginase, leads to a decrease in the fluorescence intensity of l-arginine/ATT-AuNPs hybrids. Upon incorporation of the arginase inhibitor l-norvaline, the fluorescence of the ATT-AuNP-based detecting system is restored. The linear range of arginase activity determination is from 0.0625 to 1.15 U/mL and the limit of detection is 0.056 U/mL. The half-maximal inhibition value IC₅₀ of l-norvaline is determined to be 5.6 mM. The practicability of this luminescent nanoswitch is validated by assaying the arginase activity in rat liver and monitoring the response of rat liver arginase to pharmacological agent. Compared to the existing fluorescent method of arginase activity assay, the approach demonstrated here does not involve any complicated technical manipulation, thereby greatly simplifying the detection steps. We propose that this AuNP-based luminescent nanoswitch would find wide applications in the field of life sciences and medicine.

Low potential manganese ions as efficient electron donors in native anoxygenic bacteria

Systematic control over molecular driving forces is essential for understanding the natural electron transfer processes as well as for improving the efficiency of the artificial mimics of energy converting enzymes. Oxygen producing photosynthesis uniquely employs manganese ions as rapid electron donors. Introducing this attribute to anoxygenic photosynthesis may identify evolutionary intermediates and provide insights to the energetics of biological water oxidation. This work presents effective environmental methods that substantially and simultaneously tune the redox potentials of manganese ions and the cofactors of a photosynthetic enzyme from native anoxygenic bacteria without the necessity of genetic modification or synthesis. A spontaneous coordination with bis-tris propane lowered the redox potential of the manganese (II) to manganese (III) transition to an unusually low value (~400 mV) at pH 9.4 and allowed its binding to the bacterial reaction center. Binding to a novel buried binding site elevated the redox potential of the primary electron donor, a dimer of bacteriochlorophylls, by up to 92 mV also at pH 9.4 and facilitated the electron transfer that is able to compete with the wasteful charge recombination. These events impaired the function of the natural electron donor and made BTP-coordinated manganese a viable model for an evolutionary alternative.

Proteomic analysis of CHO cell lines producing high and low quantities of a recombinant antibody before and after selection with methotrexate

High levels of recombinant protein production in Chinese hamster ovary (CHO) cells can be achieved by amplification of transgenes using the dihydrofolate reductase/methotrexate (DHFR/MTX) system. With the aim to identify predictive markers enabling the preselection of suitable high producing clones we investigated the impact of MTX-based gene amplification on two CHO cells lines producing different levels of a human monoclonal antibody by carrying out a comparative proteome analysis. The difference in antibody yield between the high and low producer was 15-fold before and 245-fold after MTX selection. Difference in-gel electrophoresis of samples from before and after MTX selection revealed 17 unique proteins that were differentially expressed between the high and low productivity lines. Of these, five proteins were differently expressed before MTX selection, representing potential markers for productivity prior to selection and for engineering processes to generate novel CHO cell line with the desirable high productivity phenotype. Fifteen proteins were differently expressed between high and low producer after MTX selection. We further found that MTX selection induced more changes in the proteome of the low producer compared to the high producer.

A five-coordinate manganese(iii) complex of a salen type ligand with a positive axial anisotropy parameter D

Quantum chemical calculations reproduced well the electronic absorption spectrum and spin Hamiltonian parameters for MnL(NCS).

Developmental competence and expression profile of genes in buffalo (Bubalus bubalis) oocytes and embryos collected under different environmental stress

The study examined the effects of different environmental stress on developmental competence and the relative abundance (RA) of various gene transcripts in oocytes and embryos of buffalo. Oocytes collected during cold period (CP) and hot period (HP) were matured, fertilized and cultured in vitro to blastocyst hatching stage. The mRNA expression patterns of genes implicated in developmental competence (OCT-4, IGF-2R and GDF-9), heat shock (HSP-70.1), oxidative stress (MnSOD), metabolism (GLUT-1), pro-apoptosis (BAX) and anti-apoptosis (BCL-2) were evaluated in immature and matured oocytes as well as in pre-implantation stage embryos. Oocytes reaching MII stage, cleavage rates, blastocyst yield and hatching rates increased (P < 0.05) during the CP. In MII oocytes and 2-cell embryos, the RA of OCT-4, IGF-2R, GDF-9, MnSOD and GLUT-1 decreased (P < 0.05) during the HP. In 4-cell embryos, the RA of OCT-4, IGF-2R and BCL-2 decreased (P < 0.05) in the HP, whereas GDF-9 increased (P < 0.05). In 8-to 16-cell embryos, the RA of OCT-4 and BCL-2 decreased (P < 0. 05) in the HP, whereas HSP-70.1 and BAX expression increased (P < 0.05). In morula and blastocyst, the RA of OCT-4, IGF-2R and MnSOD decreased (P < 0.05) during the HP, whereas HSP-70.1 was increased (P < 0.05). In conclusion, deleterious seasonal effects induced at the GV-stage carry-over to subsequent embryonic developmental stages and compromise oocyte developmental competence and quality of developed blastocysts.

A water-soluble and water-coordinated Mn(II) complex: synthesis, characterization and phantom MRI image study

Ligand H4bedik was reacted with MnCl2·4H2O at pH ∼ 6.5 to give a highly water-soluble and water-coordinated Mn(ii) complex (). The complex was found to show r1 = 3.11 mM(-1) s(-1) per Mn(ii) at 1.4 T and 6.26 mM(-1) s(-1) per Mn(ii) at 14.1 T at 25 °C, pH = 7.4. In addition to r1, the r2 at 14.1 T was found to be 132.78 mM(-1) s(-1) per Mn(ii) at 25 °C, pH = 7.4.

The Evolution of New Catalytic Mechanisms for Xenobiotic Hydrolysis in Bacterial Metalloenzymes

An increasing number of bacterial metalloenzymes have been shown to catalyse the breakdown of xenobiotics in the environment, while others exhibit a variety of promiscuous xenobiotic-degrading activities. Several different evolutionary processes have allowed these enzymes to gain or enhance xenobiotic-degrading activity. In this review, we have surveyed the range of xenobiotic-degrading metalloenzymes, and discuss the molecular and catalytic basis for the development of new activities. We also highlight how our increased understanding of the natural evolution of xenobiotic-degrading metalloenzymes can be been applied to laboratory enzyme design.

Association investigation of BACH2 rs3757247 and SOD2 rs4880 polymorphisms with the type 1 diabetes and diabetes long-term complications risk in the Polish population

Genetic factors are indicated in the development of type 1 diabetes (DM1). Recently, nucleotide variants of BACH2 and SOD2 have been associated with this chronic condition. Therefore, the purpose of the present study was to investigate the contribution of BACH2 rs3757247 and SOD2 rs4880 (Ala16Val) polymorphisms to the risk of DM1 and diabetes long-term complications. Selected polymorphic variants of BACH2 and SOD2 were investigated in a group of 141 patients with DM1 and in a group of age, gender-matched healthy subjects (n=369) using a high-resolution melting curve method. There was no evidence for either allelic or genotypic association with the risk of DM1 and diabetes chronic complications for analysed polymorphisms. In addition, no interaction between BACH2 and SOD2 variants in the development of this condition was observed. However, the frequency of BACH2 rs3757247 AG and AA genotypes was statistically different between DM1 patients with retinopathy and healthy individuals (odds ratio, 2.455; 95% confidence interval, 0.999-6.035; P=0.044), but this result did not survive multiple testing corrections. The present study did not confirm the involvement of BACH2 rs3757247 and SOD2 rs4880 polymorphisms in the development of DM1 and diabetes long-term complications. Further studies in a larger population sample are required.

Nanometric distance measurements between Mn(ii)DOTA centers

The distance between two Mn(ii)DOTA complexes attached to the ends of polyproline helices of varying lengths was measured by 94 GHz PELDOR spectroscopy with good accuracy demonstrating their effectiveness as spin-labels.

A current review for biological monitoring of manganese with exposure, susceptibility, and response biomarkers

People can be easily exposed to manganese (Mn), the twelfth most abundant element, through various exposure routes. However, overexposure to Mn causes manganism, a motor syndrome similar to Parkinson disease, via interference of the several neurotransmitter systems, particularly the dopaminergic system in areas. At cellular levels, Mn preferentially accumulates in mitochondria and increases the generation of reactive oxygen species, which changes expression and activity of manganoproteins. Many studies have provided invaluable insights into the causes, effects, and mechanisms of the Mn-induced neurotoxicity. To regulate Mn exposure, many countries have performed biological monitoring of Mn with three major biomarkers: exposure, susceptibility, and response biomarkers. In this study, we review current statuses of Mn exposure via various exposure routes including food, high susceptible population, effects of genetic polymorphisms of metabolic enzymes or transporters (CYP2D6, PARK9, SLC30A10, etc.), alterations of the Mn-responsive proteins (i.e., glutamine synthetase, Mn-SOD, metallothioneins, and divalent metal trnsporter1), and epigenetic changes due to the Mn exposure. To minimize the effects of Mn exposure, further biological monitoring of Mn should be done with more sensitive and selective biomarkers.

Developmental competence and expression pattern of bubaline (Bubalus bubalis) oocytes subjected to elevated temperatures during meiotic maturation in vitro

OBJECTIVE

To determine the direct effect of physiologically relevant high temperatures (40.5 and 41.5 °C) for two time periods (12 and 24 h) on bubaline oocytes during in vitro maturation.

METHOD

The control group oocytes were cultured at 38.5 °C for 24 h. The treatment 1 (T1) and 3 (T3) group oocytes were cultured at 40.5 and 41.5 °C respectively, for the first 12 h and at 38.5 °C for rest of the 12 h. However, treatment 2 (T2) and 4 (T4) group oocytes were cultured at 40.5 and 41.5 °C for complete 24 h.

RESULTS

Development of oocytes to blastocyst was severely compromised (p < 0.001) when matured at 40.5 and 41.5 °C for both exposure periods (12 h and 24 h). It was found that the cleavage rates, blastocyst yield and mean cell number decreased remarkably (p < 0.001) in the treatment groups compared to control. The relative mRNA expression of heat shock protein (Hsp 70.1, 70.2, 70.8, 60, 10 and HSF1), pro-apoptotic (caspases-3, -7, -8, Bid and Bax) and oxidative stress (iNOS) related genes was significantly higher (p < 0.05) in all the treatment groups compared to control. However, mRNA abundance of anti-apoptotic (Bcl-2, Mcl-1, Bcl-xl), glucose transport (Glut1, Glut3 and IGF1R), developmental competence (ZAR1 and BMP15) and oxidative stress (MnSOD) related genes was significantly decreased (p < 0.05) in the treatment groups compared to control.

CONCLUSION

The present study clearly establishes that physiologically relevant elevated temperatures during in vitro meiotic maturation reduce developmental competence of bubaline oocytes.

Taking into Account the Ion-induced Dipole Interaction in the Nonbonded Model of Ions

Metal ions exist in almost half of the proteins in the protein databank and they serve as structural, electron-transfer and catalytic elements in the metabolic processes of organisms. Molecular Dynamics (MD) simulation is a powerful tool that provides information about biomolecular systems at the atomic level. Coupled with the growth in computing power, algorithms like the Particle Mesh Ewald (PME) method have become the accepted standard when dealing with long-range interactions in MD simulations. The nonbonded model of metal ions consists of an electrostatic plus 12-6 Lennard Jones (LJ) potential and is used largely because of its speed relative to more accurate models. In previous work we found that ideal parameters do not exist that reproduce several experimental properties for M(II) ions simultaneously using the nonbonded model coupled with the PME method due to the underestimation of metal ion-ligand interactions. Via a consideration of the nature of the nonbonded model, we proposed that the observed error largely arises from overlooking charge-induced dipole interactions. The electrostatic plus 12-6 LJ potential model works reasonably well for neutral systems but does struggle with more highly charged systems. In the present work we designed and parameterized a new nonbonded model for metal ions by adding a 1/r4 term to the 12-6 model. We call it the 12-6-4 LJ-type nonbonded model due to its mathematical construction. Parameters were determined for 16 +2 metal ions for the TIP3P, SPC/E and TIP4PEW water models. The final parameters reproduce the experimental hydration free energies (HFE), ion-oxygen distances (IOD) in the first solvation shell and coordination numbers (CN) accurately for the metal ions investigated. Preliminary tests on MgCl2 at different concentrations in aqueous solution and Mg2+--nucleic acid systems show reasonable results suggesting that the present parameters can work in mixed systems. The 12-6-4 LJ-type nonbonded model is readily adopted into standard force fields like AMBER, CHARMM and OPLS-AA with only a modest computational overhead. The new nonbonded model doesn't consider charge-transfer effects explicitly and, hence, may not suitable for the simulation of systems where charge-transfer effects play a decisive role.