Direct detection of coupled proton and electron transfers in human manganese superoxide dismutase

The role of Tyr34 in proton coupled electron transfer and product inhibition of manganese superoxide dismutase

Human manganese superoxide dismutase (MnSOD) plays a crucial role in controlling levels of reactive oxygen species (ROS) by converting superoxide (O 2 ∙ - ) to molecular oxygen (O2) and hydrogen peroxide (H2O2) with proton-coupled electron transfers (PCETs). A key catalytic residue, Tyr34, determines the activity of human MnSOD and also becomes post-translationally inactivated by nitration in various diseases associated with mitochondrial dysfunction. Tyr34 has an unusual pKa due to its proximity to the Mn metal and undergoes cyclic deprotonation and protonation events to promote the electron transfers of MnSOD. Neutron diffraction, X-ray spectroscopy, and quantum chemistry calculations in oxidized, reduced and product inhibited enzymatic states shed light on the role of Tyr34 in MnSOD catalysis. The data identify the contributions of Tyr34 in MnSOD activity that support mitochondrial function and give a thorough characterization of how a single tyrosine modulates PCET catalysis. Product inhibition occurs by an associative displacement mechanism.

Metal Ion Signaling in Biomedicine

Complex multicellular organisms are composed of distinct tissues involving specialized cells that can perform specific functions, making such life forms possible. Species are defined by their genomes, and differences between individuals within a given species directly result from variations in their genetic codes. While genetic alterations can give rise to disease-causing acquisitions of distinct cell identities, it is now well-established that biochemical imbalances within a cell can also lead to cellular dysfunction and diseases. Specifically, nongenetic chemical events orchestrate cell metabolism and transcriptional programs that govern functional cell identity. Thus, imbalances in cell signaling, which broadly defines the conversion of extracellular signals into intracellular biochemical changes, can also contribute to the acquisition of diseased cell states. Metal ions exhibit unique chemical properties that can be exploited by the cell. For instance, metal ions maintain the ionic balance within the cell, coordinate amino acid residues or nucleobases altering folding and function of biomolecules, or directly catalyze specific chemical reactions. Thus, metals are essential cell signaling effectors in normal physiology and disease. Deciphering metal ion signaling is a challenging endeavor that can illuminate pathways to be targeted for therapeutic intervention. Here, we review key cellular processes where metal ions play essential roles and describe how targeting metal ion signaling pathways has been instrumental to dissecting the biochemistry of the cell and how this has led to the development of effective therapeutic strategies.

Why Bestatin Prefers Human Carnosinase 2 (CN2) to Human Carnosinase 1 (CN1)

Human carnosinases (CNs) are Xaa-His metal-ion-activated aminopeptidases that break down bioactive carnosine and other histidine-containing dipeptides. Carnosine is a bioactive peptide found in meat and prevalently used as a supplement and in functional food formulation. Nonetheless, carnosine is digested by CNs rapidly after ingestion. CNs have two isoforms (carnosinase 1 (CN1) and carnosinase 2 (CN2)), where CN1 is the main player in carnosine digestion. CNs contain a catalytic metal ion pair (Zn2+ for CN1 and Mn2+ for CN2) and two subpockets (S1 and S1' pockets) to accommodate a substrate. Bestatin (BES) has been reported to be active for CN2; however, its inhibition ability for CN1 has remained under debate, because the underlying mechanism remains unclear. This information is important for designing novel CN1-selective inhibitors for proliferating carnosine after ingestion. Thus, molecular dynamics (MD) simulations were performed to explore the binding mechanism of BES to both CN1 and CN2. The binding of BES-CN1 and BES-CN2 was studied in comparison. The results indicated that BES could bind both CNs with different degrees of binding affinity. BES prefers CN2 because: (1) its aryl terminus is trapped by Y197 in an S1 pocket; (ii) the BES polar backbone is firmly bound by catalytic Mn2+ ions; and (iii) the S1' pocket can shrink to accommodate the isopropyl end of BES. In contrast, the high mobility of the aryl end and the complete loss of metal-BES interactions in CN1 cause a loose BES binding. Seemingly, polar termini were required for a good CN1 inhibitor.

The repertoire of iron superoxide dismutases from Leishmania infantum as targets in the search for therapeutic agents against leishmaniasis

Species of Leishmania and Trypanosoma genera are the causative agents of relevant parasitic diseases. Survival inside their hosts requires the existence of a potent antioxidant enzymatic machinery. Four iron superoxide dismutases have been described in trypanosomatids (FeSODA, FeSODB1, FeSODB2, and FeSODC) that hold a potential as therapeutic targets. Nonetheless, very few studies have been developed that make use of the purified enzymes. Moreover, FeSODC remains uncharacterised in Leishmania. In this work, for the first time, we describe the purification and enzymatic activity of recombinant versions of the four Leishmania FeSOD isoforms and establish an improved strategy for developing inhibitors. We propose a novel parameter [(V*cyt. c - Vcyt. c)/Vcyt. c] which, in contrast to that used in the classical cytochrome c reduction assay, correlates linearly with enzyme concentration. As a proof of concept, we determine the IC50 values of two ruthenium carbosilane metallodendrimers against these isoforms.

Quantum refinement in real and reciprocal space using the Phenix and ORCA software

X-ray and neutron crystallography, as well as cryogenic electron microscopy (cryo-EM), are the most common methods to obtain atomic structures of biological macromolecules. A feature they all have in common is that, at typical resolutions, the experimental data need to be supplemented by empirical restraints, ensuring that the final structure is chemically reasonable. The restraints are accurate for amino acids and nucleic acids, but often less accurate for substrates, inhibitors, small-molecule ligands and metal sites, for which experimental data are scarce or empirical potentials are harder to formulate. This can be solved using quantum mechanical calculations for a small but interesting part of the structure. Such an approach, called quantum refinement, has been shown to improve structures locally, allow the determination of the protonation and oxidation states of ligands and metals, and discriminate between different interpretations of the structure. Here, we present a new implementation of quantum refinement interfacing the widely used structure-refinement software Phenix and the freely available quantum mechanical software ORCA. Through application to manganese superoxide dismutase and V- and Fe-nitrogenase, we show that the approach works effectively for X-ray and neutron crystal structures, that old results can be reproduced and structural discrimination can be performed. We discuss how the weight factor between the experimental data and the empirical restraints should be selected and how quantum mechanical quality measures such as strain energies should be calculated. We also present an application of quantum refinement to cryo-EM data for particulate methane monooxygenase and show that this may be the method of choice for metal sites in such structures because no accurate empirical restraints are currently available for metals.

SIRT5 mutants reveal the role of conserved asparagine and glutamine residues in the NAD+-binding pocket

SIRT5, one of the mammalian sirtuins, specifically recognizes succinyl-lysine residues on proteins and catalyzes the desuccinylation reaction. In this study, we characterized SIRT5 mutants with hydrophobic amino acid substitutions at Q140 and N141, in addition to the catalytic residue H158, known as an active site residue, by the Michaelis-Menten analysis and X-ray crystallography. Kinetic analysis showed that the catalytic efficiency (kcat/Km) of the Q140L and N141V mutants decreased to 0.02 times and 0.0038 times that of the wild-type SIRT5, respectively, with the activity of the N141V mutant becoming comparable to that of the H158M mutant. Our findings indicate that N141 contributes significantly to the desuccinylation reaction.

Fisetin disrupts mitochondrial homeostasis via superoxide dismutase 2 acetylation in pancreatic adenocarcinoma

Pancreatic adenocarcinoma (PDAC) is one of the most lethal malignant tumors with an urgent need for precision medicine strategies. The present study seeks to assess the antitumor effects of fisetin, and characterize its impact on PDAC. Multi-omic approaches include proteomic, transcriptomic, and metabolomic analyses. Further validation includes the assessment of mitochondria-derived reactive oxygen species (mtROS), mitochondrial membrane potential, as well as ATP generation. Molecular docking, immunoprecipitation, and proximity ligation assay were used to detect the interactions among fiseitn, superoxide dismutase 2 (SOD2), and sirtuin 2 (SIRT2). We showed that fisetin disrupted mitochondrial homeostasis and induced SOD2 acetylation in PDAC. Further, we produced site mutants to determine that fisetin-induced mtROS were dependent on SOD2 acetylation. Fisetin inhibited SIRT2 expression, thus blocking SOD2 deacetylation. SIRT2 overexpression could impede fisetin-induced SOD2 acetylation. Additionally, untargeted metabolomic analysis revealed an acceleration of folate metabolism with fisetin. Collectively, our findings suggest that fisetin disrupts mitochondrial homeostasis, eliciting an important cancer-suppressive role; thus, fisetin may serve as a promising therapeutic for PDAC.

Role and mechanisms of mast cells in brain disorders

Mast cells serve as crucial effector cells within the innate immune system and are predominantly localized in the skin, airways, gastrointestinal tract, urinary and reproductive tracts, as well as in the brain. Under physiological conditions, brain-resident mast cells secrete a diverse array of neuro-regulatory mediators to actively participate in neuroprotection. Meanwhile, as the primary source of molecules causing brain inflammation, mast cells also function as the "first responders" in brain injury. They interact with neuroglial cells and neurons to facilitate the release of numerous inflammatory mediators, proteases, and reactive oxygen species. This process initiates and amplifies immune-inflammatory responses in the brain, thereby contributing to the regulation of neuroinflammation and blood-brain barrier permeability. This article provides a comprehensive overview of the potential mechanisms through which mast cells in the brain may modulate neuroprotection and their pathological implications in various neurological disorders. It is our contention that the inhibition of mast cell activation in brain disorders could represent a novel avenue for therapeutic breakthroughs.

Bacillus subtilis fmbj ameliorates lipopolysaccharide-induced intestinal dysfunction in broilers by enhancing the SIRT1/PGC1α pathway

This study aimed to explore the impact of dietary Bacillus subtilis fmbj (BS) supplementation on acute intestinal dysfunction induced by lipopolysaccharide (LPS) in broilers. One hundred and eighty 1-day-old male Arbor Acres broilers were randomly divided into three treatment groups, each comprising ten replicates of 6 birds. On d 20, LPS-challenged (LPS group and LPS-BS group) and LPS-unchallenged (CON group) broilers received intraperitoneal injections of 1 mg/kg body weight LPS solution and an equivalent volume of sterile saline, respectively. Compared to the CON group, LPS disrupted (P < 0.05) the morphology of the small intestine (jejunum or ileum), exacerbated (P < 0.05) serum, small intestinal, and small intestinal mitochondrial antioxidant capacity, induced (P < 0.05) small intestinal oxidative damage, and altered (P < 0.05) the expression of genes and proteins related to antioxidants, cell adhesion, and mitochondrial function in the jejunum. The LPS-BS group exhibited a tendency towards improvement in small intestinal morphology, serum, small intestinal, and small intestinal mitochondrial antioxidant capacity, small intestinal oxidative damage, and the expression of genes and proteins related to antioxidants, cell adhesion, and mitochondrial function in the jejunum when compared to the LPS group. In conclusion, BS supplementation may confer protection against LPS-induced acute intestinal dysfunction in broilers by enhancing the activation of SIRT1/PGC1α, suggesting its potential as a valuable additive for the poultry industry.

Nano-enzyme functionalized hydrogels promote diabetic wound healing through immune microenvironment modulation

Non-healing diabetic wounds often culminate in amputation and mortality. The main pathophysiological features in diabetic wounds involve the accumulation of M1-type macrophages and excessive oxidative stress. In this study, we engineered a nano-enzyme functionalized hydrogel by incorporating a magnesium ion-doped molybdenum-based polymetallic oxide (Mg-POM), a novel bioactive nano-enzyme, into a GelMA hydrogel, to obtain the GelMA@Mg-POM system to enhance diabetic wound healing. GelMA@Mg-POM was crosslinked using UV light, yielding a hydrogel with a uniformly porous three-dimensional mesh structure. In vitro experiments showed that GelMA@Mg-POM extraction significantly enhanced human umbilical vein endothelial cell (HUVEC) migration, scavenged ROS, improved the inflammatory microenvironment, induced macrophage reprogramming towards M2, and promoted HUVEC regeneration of CD31 and fibroblast regeneration of type I collagen. In in vivo experiments, diabetic rat wounds treated with GelMA@Mg-POM displayed enhanced granulation tissue genesis and collagen production, as evidenced by HE and Masson staining. Immunohistochemistry demonstrated the ability of GelMA@Mg-POM to mitigate macrophage-associated inflammatory responses and promote angiogenesis. Overall, these findings suggest that GelMA@Mg-POM holds significant promise as a biomaterial for treating diabetic wounds.

Revealing the atomic and electronic mechanism of human manganese superoxide dismutase product inhibition

Human manganese superoxide dismutase (MnSOD) is a crucial oxidoreductase that maintains the vitality of mitochondria by converting superoxide (O2●-) to molecular oxygen (O2) and hydrogen peroxide (H2O2) with proton-coupled electron transfers (PCETs). Human MnSOD has evolved to be highly product inhibited to limit the formation of H2O2, a freely diffusible oxidant and signaling molecule. The product-inhibited complex is thought to be composed of a peroxide (O22-) or hydroperoxide (HO2-) species bound to Mn ion and formed from an unknown PCET mechanism. PCET mechanisms of proteins are typically not known due to difficulties in detecting the protonation states of specific residues that coincide with the electronic state of the redox center. To shed light on the mechanism, we combine neutron diffraction and X-ray absorption spectroscopy of the product-bound, trivalent, and divalent states of the enzyme to reveal the positions of all the atoms, including hydrogen, and the electronic configuration of the metal ion. The data identifies the product-inhibited complex, and a PCET mechanism of inhibition is constructed.

The role of Tyr34 in proton-coupled electron transfer of human manganese superoxide dismutase

Human manganese superoxide dismutase (MnSOD) plays a crucial role in controlling levels of reactive oxygen species (ROS) by converting superoxide (O 2 •- ) to molecular oxygen (O 2 ) and hydrogen peroxide (H 2 O 2 ) with proton-coupled electron transfers (PCETs). The reactivity of human MnSOD is determined by the state of a key catalytic residue, Tyr34, that becomes post-translationally inactivated by nitration in various diseases associated with mitochondrial dysfunction. We previously reported that Tyr34 has an unusual pK a due to its proximity to the Mn metal and undergoes cyclic deprotonation and protonation events to promote the electron transfers of MnSOD. To shed light on the role of Tyr34 MnSOD catalysis, we performed neutron diffraction, X-ray spectroscopy, and quantum chemistry calculations of Tyr34Phe MnSOD in various enzymatic states. The data identifies the contributions of Tyr34 in MnSOD activity that support mitochondrial function and presents a thorough characterization of how a single tyrosine modulates PCET catalysis.

Transition-Metal-Based Nanozymes: Synthesis, Mechanisms of Therapeutic Action, and Applications in Cancer Treatment

Cancer, as one of the leading causes of death worldwide, drives the advancement of cutting-edge technologies for cancer treatment. Transition-metal-based nanozymes emerge as promising therapeutic nanodrugs that provide a reference for cancer therapy. In this review, we present recent breakthrough nanozymes for cancer treatment. First, we comprehensively outline the preparation strategies involved in creating transition-metal-based nanozymes, including hydrothermal method, solvothermal method, chemical reduction method, biomimetic mineralization method, and sol-gel method. Subsequently, we elucidate the catalytic mechanisms (catalase (CAT)-like activities), peroxidase (POD)-like activities), oxidase (OXD)-like activities) and superoxide dismutase (SOD)-like activities) of transition-metal-based nanozymes along with their activity regulation strategies such as morphology control, size manipulation, modulation, composition adjustment and surface modification under environmental stimulation. Furthermore, we elaborate on the diverse applications of transition-metal-based nanozymes in anticancer therapies encompassing radiotherapy (RT), chemodynamic therapy (CDT), photodynamic therapy (PDT), photothermal therapy (PTT), sonodynamic therapy (SDT), immunotherapy, and synergistic therapy. Finally, the challenges faced by transition-metal-based nanozymes are discussed alongside future research directions. The purpose of this review is to offer scientific guidance that will enhance the clinical applications of nanozymes based on transition metals.

Mitochondrial-targeting and NIR-responsive Mn3O4@PDA@Pd-SS31 nanozymes reduce oxidative stress and reverse mitochondrial dysfunction to alleviate osteoarthritis

Mitochondrial reactive oxygen species (mROS) play a crucial role in the process of osteoarthritis (OA), which may be a promising target for therapy of OA. In this study, novel mitochondrial-targeting and SOD-mimic Mn3O4@PDA@Pd-SS31 nanozymes with near-infrared (NIR) responsiveness and synergistic cascade to scavenge mROS were designed for the therapy of OA. Results showed that the nanozymes accelerated the release of Pd and Mn3O4 under NIR irradiation, exhibiting enhanced activities of SOD and CAT mimic enzymes with reversed mitochondrial dysfunction and promoted mitophagy to effectively scavenge mROS from chondrocytes, modulate the microenvironment of oxidative stress, and eventually inhibit the inflammatory response. Nanozymes were excreted in vivo through intestinal metabolic pathway and had good biocompatibility, effectively reducing the inflammatory response and relieving articular cartilage degeneration in OA joints, with a reduction of 93.7 % and 93.8 % in OARSCI scores for 4 and 8 weeks respectively. Thus, this study demonstrated that the mitochondria targeting and NIR responsive Mn3O4@PDA@Pd-SS31 nanozymes could efficiently scavenge mROS, repair damaged mitochondrial function and promote cartilage regeneration, which are promising for the treatment of OA in clinical applications.

Revealing the atomic and electronic mechanism of human manganese superoxide dismutase product inhibition

Human manganese superoxide dismutase (MnSOD) is a crucial oxidoreductase that maintains the vitality of mitochondria by converting O 2 ∙ - to O 2 and H 2 O 2 with proton-coupled electron transfers (PCETs). Since changes in mitochondrial H 2 O 2 concentrations are capable of stimulating apoptotic signaling pathways, human MnSOD has evolutionarily gained the ability to be highly inhibited by its own product, H 2 O 2 . A separate set of PCETs is thought to regulate product inhibition, though mechanisms of PCETs are typically unknown due to difficulties in detecting the protonation states of specific residues that coincide with the electronic state of the redox center. To shed light on the underlying mechanism, we combined neutron diffraction and X-ray absorption spectroscopy of the product-bound, trivalent, and divalent states to reveal the all-atom structures and electronic configuration of the metal. The data identifies the product-inhibited complex for the first time and a PCET mechanism of inhibition is constructed.

Revealing the atomic and electronic mechanism of human manganese superoxide dismutase product inhibition

Human manganese superoxide dismutase (MnSOD) is a crucial oxidoreductase that maintains the vitality of mitochondria by converting O 2 ●- to O 2 and H 2 O 2 with proton-coupled electron transfers (PCETs). Since changes in mitochondrial H 2 O 2 concentrations are capable of stimulating apoptotic signaling pathways, human MnSOD has evolutionarily gained the ability to be highly inhibited by its own product, H 2 O 2 . A separate set of PCETs is thought to regulate product inhibition, though mechanisms of PCETs are typically unknown due to difficulties in detecting the protonation states of specific residues that coincide with the electronic state of the redox center. To shed light on the underlying mechanism, we combined neutron diffraction and X-ray absorption spectroscopy of the product-bound, trivalent, and divalent states to reveal the all-atom structures and electronic configuration of the metal. The data identifies the product-inhibited complex for the first time and a PCET mechanism of inhibition is constructed.

Role of oxidative stress in neurodegenerative disorders: a review of reactive oxygen species and prevention by antioxidants

Neurological disorders include a variety of conditions, including Alzheimer's disease, motor neuron disease and Parkinson's disease, affecting longevity and quality of life, and their pathogenesis is associated with oxidative stress. Several of the chronic neurodegenerative pathologies of the CNS share some common features, such as oxidative stress, inflammation, synapse dysfunctions, protein misfolding and defective autophagia. Neuroinflammation can involve the activation of mast cells, contributing to oxidative stress, in addition to other sources of reactive oxygen species. Antioxidants can powerfully neutralize reactive oxygen species and free radicals, decreasing oxidative damage. Antioxidant genes, like the manganese superoxide dismutase enzyme, can undergo epigenetic changes that reduce their expression, thus increasing oxidative stress in tissue. Alternatively, DNA can be altered by free radical damage. The epigenetic landscape of these genes can change antioxidant function and may result in neurodegenerative disease. This imbalance of free radical production and antioxidant function increases the reactive oxygen species that cause cell damage in neurons and is often observed as an age-related event. Increased antioxidant expression in mice is protective against reactive oxygen species in neurons as is the exogenous supplementation of antioxidants. Manganese superoxide dismutase requires manganese for its enzymic function. Antioxidant therapy is considered for age-related neurodegenerative diseases, and a new mimetic of a manganese superoxide dismutase, avasopasem manganese, is described and suggested as a putative treatment to reduce the oxidative stress that causes neurodegenerative disease. The aim of this narrative review is to explore the evidence that oxidative stress causes neurodegenerative damage and the role of antioxidant genes in inhibiting reactive oxygen species damage. Can the neuronal environment of oxidative stress, causing neuroinflammation and neurodegeneration, be reduced or reversed?

Interfacial assembly of chitin/Mn3O4 composite hydrogels as photothermal antibacterial platform for infected wound healing

To combat bacteria and even biofilm infections, developing alternative antibacterial wound dressings independent of antibiotics is imperative. Herein, this study developed a series of bioactive chitin/Mn3O4 composite hydrogels under mild conditions for infected wound healing application. The in situ synthesized Mn3O4 NPs homogeneously distribute throughout chitin networks and strongly interact with chitin matrix, and as well as endow the chitin/Mn3O4 hydrogels with NIR-assisted outstanding photothermal antibacterial and antibiofilm activities. Meantime, the chitin/Mn3O4 hydrogels exhibit favorable biocompatibility and antioxidant property. Furthermore, the chitin/Mn3O4 hydrogels with the assist of NIR show an excellent skin wound healing performance in a mouse full-thickness S. aureus biofilms-infected wound model, by accelerating the phase transition from inflammation to remodeling. This study broadens the scope for the fabrication of chitin hydrogels with antibacterial property, and offers an excellent alternative for the bacterial-associated wound infection therapy.

A nucleotide-copper(II) complex possessing a monooxygenase-like catalytic function

The de novo design of artificial biocatalysts with enzyme-like active sites and catalytic functions has long been an attractive yet challenging goal. In this study, we present a nucleotide-Cu²⁺ complex, synthesized through a one-pot approach, capable of catalyzing ortho-hydroxylation reactions resembling those of minimalist monooxygenases. Both experimental and theoretical findings demonstrate that the catalyst, in which Cu²⁺ coordinates with both the nucleobase and phosphate moieties, forms a ternary-complex intermediate with H₂O₂ and tyramine substrates through multiple weak interactions. The subsequent electron transfer and hydrogen (or proton) transfer steps lead to the ortho-hydroxylation of tyramine, where the single copper center exhibits a similar function to natural dicopper sites. Moreover, Cu²⁺ bound to nucleotides or oligonucleotides exhibits thermophilic catalytic properties within the temperature range of 25 °C to 75 °C, while native enzymes are fully deactivated above 35 °C. This study may provide insights for the future design of oxidase-mimetic catalysts and serve as a guide for the design of primitive metallocentre-dependent enzymes.

Perfect Crystals: microgravity capillary counterdiffusion crystallization of human manganese superoxide dismutase for neutron crystallography

The NASA mission Perfect Crystals used the microgravity environment on the International Space Station (ISS) to grow crystals of human manganese superoxide dismutase (MnSOD)-an oxidoreductase critical for mitochondrial vitality and human health. The mission's overarching aim is to perform neutron protein crystallography (NPC) on MnSOD to directly visualize proton positions and derive a chemical understanding of the concerted proton electron transfers performed by the enzyme. Large crystals that are perfect enough to diffract neutrons to sufficient resolution are essential for NPC. This combination, large and perfect, is hard to achieve on Earth due to gravity-induced convective mixing. Capillary counterdiffusion methods were developed that provided a gradient of conditions for crystal growth along with a built-in time delay that prevented premature crystallization before stowage on the ISS. Here, we report a highly successful and versatile crystallization system to grow a plethora of crystals for high-resolution NPC.

Multifunctional Integrated Nanozymes Facilitate Spinal Cord Regeneration by Remodeling the Extrinsic Neural Environment

High levels of reactive oxygen species (ROS) and inflammation create a complicated extrinsic neural environment that dominates the initial post-injury period after spinal cord injury (SCI). The compensatory pathways between ROS and inflammation limited the efficacy of modulating the above single treatment regimen after SCI. Here, novel "nanoflower" Mn3 O4 integrated with "pollen" IRF-5 SiRNA was designed as a combination antioxidant and anti-inflammatory treatment after SCI. The "nanoflower" and "pollen" structure was encapsulated with a neutrophil membrane for protective and targeted delivery. Furthermore, valence-engineered nanozyme Mn3 O4 imitated the cascade response of antioxidant enzymes with a higher substrate affinity compared to natural antioxidant enzymes. Nanozymes effectively catalyzed ROS to generate O2 , which is advantageous for reducing oxidative stress and promoting angiogenesis. The screened "pollen" IRF-5 SiRNA could reverse the inflammatory phenotype by reducing interferon regulatory factors-5 (IRF-5) expression (protein level: 73.08% and mRNA level: 63.10%). The decreased expression of pro-inflammatory factors reduced the infiltration of inflammatory cells, resulting in less neural scarring. In SCI rats, multifunctional nanozymes enhanced the proliferation of various neuronal subtypes (motor neurons, interneurons, and sensory neurons) and the recovery of locomotor function, demonstrating that the remodeling of the extrinsic neural environment is a promising strategy to facilitate nerve regeneration.

Exploring the structural and dynamic differences between human carnosinase I (CN1) and II (CN2)

Human carnosinases (CNs) are dimeric dipeptidases in the metallopeptidase M20 family. Two isoforms of carnosinases (Zn²⁺ -containing carnosinase 1 (CN1) found in serum and Mn²⁺ -carnosinase 2 (CN2) in tissue) were identified. Both CNs cleave histidine-containing (Xaa-His) dipeptides such as carnosine where CN2 was found to accept a broader spectrum of substrates. A loss of CN function, resulting in a high carnosine concentration, reduces risk for diabetes and neurological disorders. Although several studies on CN activities and its Michaelis complex were conducted, all shed the light on CN1 activity where the CN2 data is limited. Also, the molecular details on CN1 and CN2 similarity and dissimilarity in structure and function remain unclear. Thus, in this work, molecular dynamics (MD) simulations were employed to study structure and dynamics of human CN1 and CN2 in comparison. The results show that the different catalytic ability of both CNs is due to their pocket size and environment. CN2 can accept a wider range of substrate due to the wider mouth of a binding pocket. The L1 loop seems to play a role in gating activity. Comparing to CN2, CN1 provides more electronegative entrance, more wettability, and higher stability of catalytic metal ion-pair in the active site which allow more efficient water-mediated catalysis. The microscopic understanding obtained here can serve as a basis for CN inhibition strategies resulting in higher carnosine levels and consequently mitigating complications associated with diseases such as diabetes and neurological disorder.

EWALD: A macromolecular diffractometer for the second target station

Revealing the positions of all the atoms in large macromolecules is powerful but only possible with neutron macromolecular crystallography (NMC). Neutrons provide a sensitive and gentle probe for the direct detection of protonation states at near-physiological temperatures and clean of artifacts caused by x rays or electrons. Currently, NMC use is restricted by the requirement for large crystal volumes even at state-of-the-art instruments such as the macromolecular neutron diffractometer at the Spallation Neutron Source. EWALD's design will break the crystal volume barrier and, thus, open the door for new types of experiments, the study of grand challenge systems, and the more routine use of NMC in biology. EWALD is a single crystal diffractometer capable of collecting data from macromolecular crystals on orders of magnitude smaller than what is currently feasible. The construction of EWALD at the Second Target Station will cause a revolution in NMC by enabling key discoveries in the biological, biomedical, and bioenergy sciences.

The Role of the Metabolism of Zinc and Manganese Ions in Human Cancerogenesis

Metal ion homeostasis is fundamental for life. Specifically, transition metals iron, manganese and zinc play a pivotal role in mitochondrial metabolism and energy generation, anti-oxidation defense, transcriptional regulation and the immune response. The misregulation of expression or mutations in ion carriers and the corresponding changes in Mn²⁺ and Zn²⁺ levels suggest that these ions play a pivotal role in cancer progression. Moreover, coordinated changes in Mn²⁺ and Zn²⁺ ion carriers have been detected, suggesting that particular mechanisms influenced by both ions might be required for the growth of cancer cells, metastasis and immune evasion. Here, we present a review of zinc and manganese pathophysiology suggesting that these ions might cooperatively regulate cancerogenesis. Zn and Mn effects converge on mitochondria-induced apoptosis, transcriptional regulation and the cGAS-STING signaling pathway, mediating the immune response. Both Zn and Mn influence cancer progression and impact treatment efficacy in animal models and clinical trials. We predict that novel strategies targeting the regulation of both Zn and Mn in cancer will complement current therapeutic strategies.

UNEXPECTED PLASTICITY OF THE QUATERNARY STRUCTURE OF IRON-MANGANESE SUPEROXIDE DISMUTASES

Protein 3D structure can be remarkably robust to the accumulation of mutations during evolution. On the other hand, sometimes a single amino acid substitution can be sufficient to generate dramatic and completely unpredictable structural consequences. In an attempt to rationally alter the preferences for the metal ion at the active site of a member of the Iron/Manganese superoxide dismutase family, two examples of the latter phenomenon were identified. Site directed mutants of SOD from Trichoderma reesei were generated and studied crystallographically together with the wild type enzyme. Despite being chosen for their potential impact on the redox potential of the metal, two of the mutations (D150G and G73A) in fact resulted in significant alterations to the protein quaternary structure. The D150G mutant presented alternative inter-subunit contacts leading to a loss of symmetry of the wild type tetramer, whereas the G73A mutation transformed the tetramer into an octamer despite not participating directly in any of the inter-subunit interfaces. We conclude that there is considerable intrinsic plasticity in the Fe/MnSOD fold that can be unpredictably affected by single amino acid substitutions. In much the same way as phenotypic defects at the organism level can reveal much about normal function, so too can such mutations teach us much about the subtleties of protein structure.

In Situ Synthesis of Natural Antioxidase Mimics for Catalytic Anti-Inflammatory Treatments: Rheumatoid Arthritis as an Example

Mimicking the coordination geometry of the active metal sites of natural enzymes is an efficient strategy in designing therapeutic chemicals with enzymelike in vivo reaction thermodynamics and kinetics. In this study, this chemical concept has been applied for the in situ synthesis of natural antioxidase mimics for catalytic anti-inflammatory treatment by using rheumatoid arthritis, a common and hardly curable immune-mediated diseases, as an example. Briefly, a composite nanomedicine has been first constructed by loading cationic porphyrin ligands into a manganese-engineered mesoporous silica nanocarrier, which can respond to a mildly acidic environment to concurrently release manganous ions and porphyrin ligands, enabling their subsequent coordination and synthesis of manganese porphyrin with a coordination environment of an active Mn site similar to those of the metal sites in natural superoxide dismutase (SOD) and catalase. Due to the strong metal-ligand exchange coupling enabled by the N-ethylpyridinium-2-yl groups tetrasubstituted in the meso positions of N4-macroheterocycles, such a manganese porphyrin presents the SOD-like activity of disproportionating superoxide anions via outer-sphere proton-coupled one-electron transfer (diaquamanganese(III)/monoaquamanganese(II) cycling), as well as the catalase-like activity of disproportionating hydrogen peroxide via inner-sphere proton-coupled two-electron transfer (diaquamanganese(III)/dioxomanganese(V) cycling). Cellular experiments demonstrated the high antioxidative efficacy of the composite nanomedicine in M1 macrophages by promoting their polarization shift to the anti-inflammatory M2 phenotype. Equally importantly, the silicon-containing oligomers released from the manganese silicate nanocarrier can act as heterogeneous nucleation centers of hydroxyapatite for facilitating biomineralization by bone mesenchymal stem cells. Finally, an in vivo adjuvant-induced arthritis animal model further reveals the high efficacy of the nanomedicine in treating rheumatoid arthritis.

Neutron crystallography reveals mechanisms used by Pseudomonas aeruginosa for host-cell binding

The opportunistic pathogen Pseudomonas aeruginosa, a major cause of nosocomial infections, uses carbohydrate-binding proteins (lectins) as part of its binding to host cells. The fucose-binding lectin, LecB, displays a unique carbohydrate-binding site that incorporates two closely located calcium ions bridging between the ligand and protein, providing specificity and unusually high affinity. Here, we investigate the mechanisms involved in binding based on neutron crystallography studies of a fully deuterated LecB/fucose/calcium complex. The neutron structure, which includes the positions of all the hydrogen atoms, reveals that the high affinity of binding may be related to the occurrence of a low-barrier hydrogen bond induced by the proximity of the two calcium ions, the presence of coordination rings between the sugar, calcium and LecB, and the dynamic behaviour of bridging water molecules at room temperature. These key structural details may assist in the design of anti-adhesive compounds to combat multi-resistance bacterial infections.

Pseudomonas aeruginosa employs lectins to bind to its host cells, and is known to be the major cause of lung infections. Lectin B (LecB) from Pseudomonas aeruginosa binds specifically to galactose and fucose and is important for pathogenicity, adhesion and biofilm formation. In this work, the neutron crystal structure (1.9 Å) of the deuterated LecB/Ca/fucose complex is reported. The structure, in combination with perdeuteration of the ligand and the receptor allowed the observation of hydrogen atoms, protonation states and hydrogen bonds involved in the interaction between pathogenic bacteria and host cells. Thus the study provides structural insights into the mechanism of high affinity binding of LecB to its targets.

Cryotrapping peroxide in the active site of human mitochondrial manganese superoxide dismutase crystals for neutron diffraction

Structurally identifying the enzymatic intermediates of redox proteins has been elusive due to difficulty in resolving the H atoms involved in catalysis and the susceptibility of ligand complexes to photoreduction from X-rays. Cryotrapping ligands for neutron protein crystallography combines two powerful tools that offer the advantage of directly identifying hydrogen positions in redox-enzyme intermediates without radiolytic perturbation of metal-containing active sites. However, translating cryogenic techniques from X-ray to neutron crystallography is not straightforward due to the large crystal volumes and long data-collection times. Here, methods have been developed to visualize the evasive peroxo complex of manganese superoxide dismutase (MnSOD) so that all atoms, including H atoms, could be visualized. The subsequent cryocooling and ligand-trapping methods resulted in neutron data collection to 2.30 Å resolution. The P6122 crystal form of MnSOD is challenging because it has some of the largest unit-cell dimensions (a = b = 77.8, c = 236.8 Å) ever studied using high-resolution cryo-neutron crystallography. The resulting neutron diffraction data permitted the visualization of a dioxygen species bound to the MnSOD active-site metal that was indicative of successful cryotrapping.

Facet-Dependent Biodegradable Mn3 O4 Nanoparticles for Ameliorating Parkinson's Disease

Parkinson's disease (PD) is a common neurodegeneration disease. Unfortunately, there are no effective measures to prevent or inhibit this disease. In this study, biodegradable Mn₃ O₄ nanoparticles (NPs) in different shapes are prepared and enclosed them by {100}, {200} and {103} facets that exhibit facet-dependent protection against neurotoxicity induced by oxidative damage in a cell model of PD. Notably, Mn₃ O₄ nanorods enclosed by {103} facets exhibit high levels of enzyme-like activity to eliminate reactive oxygen specie in vitro. It is also determined that the uptake pathway of Mn₃ O₄ NPs into MN9D cells is mediated by caveolin. The data demonstrate that Mn₃ O₄ nanorods can be taken up by cells effectively and confer excellent levels of neuroprotection while the biodegradation of Mn₃ O₄ NPs in vivo is confirmed by photoacoustic image of Mn₃ O₄ NPs in brain at 60 d. Furthermore, the oxygen scavenging effect created by Mn₃ O₄ nanorods is successfully applied to a mouse model of PD; the amount of α-synuclein in the cerebrospinal fluid of PD mice is reduced by 61.2% in two weeks, thus demonstrating the potential application of facet-directed Mn₃ O₄ NPs for the clinical therapy of neurodegenerative disease.

Fed-batch production of deuterated protein in Escherichia coli for neutron scattering experimentation

Neutron scattering is a powerful technique for determining the structure and dynamics of biological materials in a variety of environmental conditions. A distinguishing property of the neutron is its sensitivity to detecting hydrogen and distinguishing it from its isotope deuterium. This enables unique types of experiments that take advantage of this differential sensitivity called isotopic contrast variation. Using this approach, the chemistry of the system is not changed, but the visibility of individual sample components can be tuned by varying the deuterium content of the system under investigation. Deuterated proteins are commonly produced in bacterial systems that are adapted to growth in D₂O minimal media. To maximize the yield of deuterium-labeled protein and efficiently utilize D₂O and occasionally the deuterated substrate, fed-batch processes are routinely used to maximize biomass production without compromising cell viability. A step-by-step procedure will be described along with a case study of the production of deuterated green fluorescent protein. Limitations of the process will also be discussed.

Metalloprotein catalysis: structural and mechanistic insights into oxidoreductases from neutron protein crystallography

Metalloproteins catalyze a range of reactions, with enhanced chemical functionality due to their metal cofactor. The reaction mechanisms of metalloproteins have been experimentally characterized by spectroscopy, macromolecular crystallography and cryo-electron microscopy. An important caveat in structural studies of metalloproteins remains the artefacts that can be introduced by radiation damage. Photoreduction, radiolysis and ionization deriving from the electromagnetic beam used to probe the structure complicate structural and mechanistic interpretation. Neutron protein diffraction remains the only structural probe that leaves protein samples devoid of radiation damage, even when data are collected at room temperature. Additionally, neutron protein crystallography provides information on the positions of light atoms such as hydrogen and deuterium, allowing the characterization of protonation states and hydrogen-bonding networks. Neutron protein crystallography has further been used in conjunction with experimental and computational techniques to gain insight into the structures and reaction mechanisms of several transition-state metal oxidoreductases with iron, copper and manganese cofactors. Here, the contribution of neutron protein crystallography towards elucidating the reaction mechanism of metalloproteins is reviewed.

Controlling the Reactivity of a Metal-Hydroxo Adduct with a Hydrogen Bond

The enzymes manganese lipoxygenase (MnLOX) and manganese superoxide dismutase (MnSOD) utilize mononuclear Mn centers to effect their catalytic reactions. In the oxidized Mn^III state, the active site of each enzyme contains a hydroxo ligand, and X-ray crystal structures imply a hydrogen bond between this hydroxo ligand and a cis carboxylate ligand. While hydrogen bonding is a common feature of enzyme active sites, the importance of this particular hydroxo-carboxylate interaction is relatively unexplored. In this present study, we examined a pair of Mn^III-hydroxo complexes that differ by a single functional group. One of these complexes, [Mn^III(OH)(PaPy₂N)]⁺, contains a naphthyridinyl moiety capable of forming an intramolecular hydrogen bond with the hydroxo ligand. The second complex, [Mn^III(OH)(PaPy₂Q)]⁺, contains a quinolinyl moiety that does not permit any intramolecular hydrogen bonding. Spectroscopic characterization of these complexes supports a common structure, but with perturbations to [Mn^III(OH)(PaPy₂N)]⁺, consistent with a hydrogen bond. Kinetic studies using a variety of substrates with activated O-H bonds, revealed that [Mn^III(OH)(PaPy₂N)]⁺ is far more reactive than [Mn^III(OH)(PaPy₂Q)]⁺, with rate enhancements of 15-100-fold. A detailed analysis of the thermodynamic contributions to these reactions using DFT computations reveals that the former complex is significantly more basic. This increased basicity counteracts the more negative reduction potential of this complex, leading to a stronger O-H BDFE in the [Mn^II(OH₂)(PaPy₂N)]⁺ product. Thus, the differences in reactivity between [Mn^III(OH)(PaPy₂Q)]⁺ and [Mn^III(OH)(PaPy₂N)]⁺ can be understood on the basis of thermodynamic considerations, which are strongly influenced by the ability of the latter complex to form an intramolecular hydrogen bond.