Zinc and the zinc proteome

Effect of Divalent Metal Ions on the Ribonuclease Activity of the Toxin Molecule HP0894 from Helicobacter pylori

Bacteria and archaea respond and adapt to environmental stress conditions by modulating the toxin-antitoxin (TA) system for survival. Within the bacterium Helicobacter pylori, the protein HP0894 is a key player in the HP0894-HP0895 TA system, in which HP0894 serves as a toxin and HP0895 as an antitoxin. HP0894 has intrinsic ribonuclease (RNase) activity that regulates gene expression and translation, significantly influencing bacterial physiology and survival. This activity is influenced by the presence of metal ions such as Mg2+. In this study, we explore the metal-dependent RNase activity of HP0894. Surprisingly, all tested metal ions lead to a reduction in RNase activity, with zinc ions (Zn2+) causing the most significant decrease. The secondary structure of HP0894 remained largely unaffected by Zn2+ binding, whereas structural rigidity was notably increased, as revealed using CD analysis. NMR characterized the Zn2+ binding, implicating numerous His, Asp, and Glu residues in HP0894. In summary, these results suggest that metal ions play a regulatory role in the RNase activity of HP0894, contributing to maintaining the toxin molecule in an inactive state under normal conditions.

Zinc is Essential for the Copper Reductase Activity of Yeast Nucleosomes

The histone H3-H4 tetramer is a copper reductase enzyme, facilitating the production of cuprous (Cu1+) ions for distribution to copper-dependent enzymes. It was, however, unknown if this enzymatic activity occurred within nucleosomes. To investigate this, we obtained native nucleosomes from Saccharomyces cerevisiae using micrococcal nuclease digestion of chromatin in isolated nuclei and ion-exchange chromatographic purification. The purified nucleosomal fragments robustly reduced Cu2+ to Cu1+ ions, with the optimal activity dependent on the presence of zinc ions. Mutation of the histone H3 histidine 113 (H3H113) residue at the active site substantially reduced the enzymatic activity of nucleosomes, underscoring the catalytic role of histone H3. Consistently, limiting zinc ions reduced intracellular Cu1+ levels and compromised growth, phenotypes that were mitigated by genetically enhancing the copper reductase activity of histone H3. These results indicate that yeast nucleosomes possess copper reductase activity, suggesting that the fundamental unit of eukaryotic chromatin is an enzyme complex.

Association of serum zinc level and clinical outcome in Egyptian COVID-19 patients

Background

Zinc is an anti-inflammatory and antioxidant micronutrient found in food. Due to its well-established role in immunity, it is currently being used in some clinical trials against coronavirus disease-2019 (COVID-19). This study aimed to assess the association between the mean serum zinc level in COVID-19 Egyptian patients and its relationship with disease severity. This cross-sectional study was conducted on sixty patients with confirmed COVID-19 infection. These patients were divided into two groups according to clinical outcome, group 1 which included 30 intensive care unit (ICU) patients and group 2 which included 30 patients who were admitted to the ward. Mean serum levels of zinc were compared between the two groups.

Results

There was a statistically significant difference noted among study groups regarding the serum zinc level (p < 0.039), where lower mean serum zinc levels were noted in ICU patients compared to ward patients (70.6 ± 5.7 vs 73.8 ± 6.1).

Conclusion

Low serum zinc level is associated with the severe outcome of COVID-19 infection.

Recent advances in the application of metallomics in diagnosis and prognosis of human cancer

Metals play a critical role in human health and diseases. In recent years, metallomics has been introduced and extensively applied to investigate the distribution, regulation, function, and crosstalk of metal(loid) ions in various physiological and pathological processes. Based on high-throughput multielemental analytical techniques and bioinformatics methods, it is possible to elucidate the correlation between the metabolism and homeostasis of diverse metals and complex diseases, in particular for cancer. This review aims to provide an overview of recent progress made in the application of metallomics in cancer research. We mainly focuses on the studies about metallomic profiling of different human biological samples for several major types of cancer, which reveal distinct and dynamic patterns of metal ion contents and the potential benefits of using such information in the detection and prognosis of these malignancies. Elevated levels of copper appear to be a significant risk factor for various cancers, and each type of cancer has a unique distribution of metals in biofluids, hair/nails, and tumor-affected tissues. Furthermore, associations between genetic variations in representative metalloprotein genes and cancer susceptibility have also been demonstrated. Overall, metallomics not only offers a better understanding of the relationship between metal dyshomeostasis and the development of cancer but also facilitates the discovery of new diagnostic and prognostic markers for cancer translational medicine.

Molecular physiology of zinc in Drosophila melanogaster

New research in Drosophila melanogaster has revealed the molecular mechanisms of zinc involvement in many biological processes. A newly discovered Metallothionein is predicted to have a higher zinc specificity than the other isoforms. Zinc negatively regulates tyrosine hydroxylase activity by antagonizing iron binding, thus rendering the enzyme ineffective or non-functional. The identification of a new chaperone of the protein disulfide isomerase family provided mechanistic insight into the protein trafficking defects caused by zinc dyshomeostasis in the secretory pathway. Insect models of tumor pathogenesis indicate that zinc regulates the structural stabilization of cells by transcriptionally regulating matrix metalloproteinases while zinc dyshomeostasis in the secretory pathway modulates cell signaling through endoplastic recticulum stress.

Zinc transporters ZIPT-2.4 and ZIPT-15 are required for normal C. elegans fecundity

PURPOSE

The requirement of zinc for the development and maturation of germ lines and reproductive systems is deeply conserved across evolution. The nematode Caenorhabditis elegans offers a tractable platform to study the complex system of distributing zinc to the germ line. We investigated several zinc importers to investigate how zinc transporters play a role in the reproductive system in nematodes, as well as establish a platform to study zinc transporter biology in germline and reproductive development.

METHODS

Previous high throughput transcriptional datasets as well as phylogenetic analysis identified several putative zinc transporters that have a function in reproduction in worms. Phenotypic analysis of CRISPR-generated knockouts and tags included characterization of offspring output, gonad development, and protein localization. Light and immunofluorescence microscopy allowed for visualization of physiological and molecular effects of zinc transporter mutations.

RESULTS

Disruption of two zinc transporters, ZIPT-2.4 and ZIPT-15, was shown to lead to defects in reproductive output. A mutation in zipt-2.4 has subtle effects on reproduction, while a mutation in zipt-15 has a clear impact on gonad and germline development that translates into a more pronounced defect in fecundity. Both transporters have germline expression, as well as additional expression in other cell types.

CONCLUSIONS

Two ZIP-family zinc transporter orthologs of human ZIP6/10 and ZIP1/2/3 proteins are important for full reproductive fecundity and participate in development of the gonad. Notably, these zinc transporters are present in gut and reproductive tissues in addition to the germ line, consistent with a complex zinc trafficking network important for reproductive success.

Effect of enteral zinc supplementation on growth and neurodevelopment of preterm infants: a systematic review and meta-analysis

OBJECTIVE

To evaluate effect of enteral zinc supplementation on growth and neurodevelopmental outcomes of preterm infants.

STUDY DESIGN

A systematic review and meta-analysis of randomized-controlled trials (RCTs) examining growth and neurodevelopmental outcomes after zinc supplementation in preterm infants.

RESULTS

Of eight RCTs involving 742 infants included, seven reported growth anthropometrics at 3-6 months corrected age (CA) and two reported neurodevelopmental outcomes at 6-12 months CA. Zinc supplementation was associated with increased weight z-score (weighted mean difference (WMD) = 0.50; 95% CI 0.23-0.76, heterogeneity I2 = 89.1%; P < 0.01), length z-score (WMD = 1.12; 95% CI 0.63-1.61, heterogeneity I2 = 96.0%; P < 0.01) and motor developmental score (WMD = 9.54; 95% CI 6.6-12.4 heterogeneity I2 = 0%; P = 0.52). There was no effect on head circumference and total developmental score. Evidence is "moderate" certainty for weight and length and "very low" certainty for neurodevelopment.

CONCLUSION

Zinc supplementation may enhance weight gain and linear growth in preterm infants. There is a lack of data about relationship between zinc supplementation and neurodevelopment.

Marginal Zinc Deficiency Alters Essential Fatty Acid Metabolism in Healthy Men

BACKGROUND

Rice biofortification with Zinc (Zn) can improve the Zn status of rice-consuming populations. However, the metabolic impact in humans consuming Zn-biofortified rice is unknown.

OBJECTIVES

To determine the effects of Zn-biofortified rice on lipid metabolism in normolipidemic men.

METHODS

The men consumed a rice-based diet containing 6 mg Zn/d and 1.5 g phytate (phytate/Zn ratio = 44) for 2 wk followed by a 10-mg Zn/d diet without phytate for 4 wk. An ad libitum diet supplemented with 25 mg Zn/d was then fed for 3 wk. Fasting blood samples were taken at baseline and at the end of each metabolic period for measuring plasma zinc, glucose, insulin, triglyceride (TG), LDL and HDL cholesterol, fatty acids, oxylipins, and fatty acid desaturase activities. Statistical differences were assessed by linear mixed model.

RESULTS

Fatty acid desaturase (FADS) 1 activity decreased by 29.1% (P = 0.007) when the 6-mg Zn/d diet was consumed for 2 wk. This change was associated with significant decreases in HDL and LDL cholesterol. The alterations in FADS1, HDL cholesterol, and TG remained unchanged when Zn intakes were increased to 10 mg/d for 4 wk. Supplementation with 25 mg Zn/d for 3 wk normalized these metabolic changes and significantly increased LDL cholesterol at the end of this metabolic period compared with baseline. FADS1 activity was inversely correlated with FADS2 (rmcorr = -0.52; P = 0.001) and TG (rmcorr = -0.55; P = 0.001) at all time points.

CONCLUSIONS

A low-zinc, high-phytate rice-based diet reduced plasma HDL cholesterol concentrations and altered fatty acid profiles in healthy men within 2 wk. Consuming 10 mg Zn/d without phytate for 4 wk did not improve the lipid profiles, but a 25-mg Zn/d supplement corrects these alterations in lipid metabolism within 3 wk.

The Effects of Essential and Non-Essential Metal Toxicity in the Drosophila melanogaster Insect Model: A Review

The biological effects of environmental metal contamination are important issues in an industrialized, resource-dependent world. Different metals have different roles in biology and can be classified as essential if they are required by a living organism (e.g., as cofactors), or as non-essential metals if they are not. While essential metal ions have been well studied in many eukaryotic species, less is known about the effects of non-essential metals, even though essential and non-essential metals are often chemically similar and can bind to the same biological ligands. Insects are often exposed to a variety of contaminated environments and associated essential and non-essential metal toxicity, but many questions regarding their response to toxicity remain unanswered. Drosophila melanogaster is an excellent insect model species in which to study the effects of toxic metal due to the extensive experimental and genetic resources available for this species. Here, we review the current understanding of the impact of a suite of essential and non-essential metals (Cu, Fe, Zn, Hg, Pb, Cd, and Ni) on the D. melanogaster metal response system, highlighting the knowledge gaps between essential and non-essential metals in D. melanogaster. This review emphasizes the need to use multiple metals, multiple genetic backgrounds, and both sexes in future studies to help guide future research towards better understanding the effects of metal contamination in general.

Tunicates Illuminate the Enigmatic Evolution of Chordate Metallothioneins by Gene Gains and Losses, Independent Modular Expansions, and Functional Convergences

To investigate novel patterns and processes of protein evolution, we have focused in the metallothioneins (MTs), a singular group of metal-binding, cysteine-rich proteins that, due to their high degree of sequence diversity, still represents a "black hole" in Evolutionary Biology. We have identified and analyzed more than 160 new MTs in nonvertebrate chordates (especially in 37 species of ascidians, 4 thaliaceans, and 3 appendicularians) showing that prototypic tunicate MTs are mono-modular proteins with a pervasive preference for cadmium ions, whereas vertebrate and cephalochordate MTs are bimodular proteins with diverse metal preferences. These structural and functional differences imply a complex evolutionary history of chordate MTs-including de novo emergence of genes and domains, processes of convergent evolution, events of gene gains and losses, and recurrent amplifications of functional domains-that would stand for an unprecedented case in the field of protein evolution.

Zinc and COVID-19: Basis of Current Clinical Trials

Coronavirus disease-2019 (COVID-19) pandemic continues to threaten patients, societies, and economic and healthcare systems around the world. Like many other diseases, the host immune system determines the progress of COVID-19 and fatality. Modulation of inflammatory response and cytokine production using immunonutrition is a novel concept that has been applied to other diseases as well. Zinc, one of the anti-inflammatory and antioxidant micronutrient found in food with well-established role in immunity, is currently being used in some clinical trials against COVID-19. This review integrates the contemporary studies of role of zinc in antiviral immunity along with discussing its potential role against COVID-19, and ongoing COVID-19 clinical trials using zinc.

InterMetalDB: A Database and Browser of Intermolecular Metal Binding Sites in Macromolecules with Structural Information

InterMetalDB is a free-of-charge database and browser of intermolecular metal binding sites that are present on the interfaces of macromolecules forming larger assemblies based on structural information deposited in Protein Data Bank (PDB). It can be found and freely used at https://intermetaldb.biotech.uni.wroc.pl/. InterMetalDB collects the interfacial binding sites with involvement of metal ions and clusters them on the basis of 50% sequence similarity and the nearest metal environment (5 Å radius). The data are available through the web interface where they can be queried, viewed, and downloaded. Complexity of the query depends on the user, because the questions in the query are connected with each other by a logical AND. InterMetalDB offers several useful options for filtering records including searching for structures by particular parameters such as structure resolution, structure description, and date of deposition. Records can be filtered by coordinated metal ion, number of bound amino acid residues, coordination sphere, and other features. InterMetalDB is regularly updated and will continue to be regularly updated with new content in the future. InterMetalDB is a useful tool for all researchers interested in metalloproteins, protein engineering, and metal-driven oligomerization.

Trace element deficiency is highly prevalent and associated with infection and mortality in patients with alcoholic hepatitis

BACKGROUND

Malnutrition is common in patients with alcohol-related liver disease and is associated with outcome in patients with alcoholic hepatitis. Trace elements (cobalt, copper, iron, selenium and zinc) are micronutrients essential for many cellular processes including antioxidant pathways. The prevalence and relevance of trace element deficiency is unknown in alcoholic hepatitis.

AIM

To determine the prevalence of trace element deficiency and its association with clinical outcomes in patients with alcoholic hepatitis.

METHODS

Serum was obtained from patients with alcoholic hepatitis, alcohol-related cirrhosis and healthy volunteers as part of clinical trials, cohort studies and a biobank. Trace element concentration was measured by inductively coupled plasma mass spectrometry. Association of trace element levels with development of infection within 90 days and mortality within 28 and 90 days was evaluated by multivariate logistic regression.

RESULTS

Sera from 302 patients with alcoholic hepatitis, 46 with alcohol-related cirrhosis and 15 healthy controls were analysed for trace element concentration. The prevalence of zinc deficiency (85%) and selenium deficiency (67%) in alcoholic hepatitis was higher than in alcohol-related cirrhosis (72% [p=0.04] and 37% [p<0.001], respectively). Zinc, selenium, copper and chromium were significantly different between groups. Iron deficiency was a predictor of development of infection within 90 days. Zinc deficiency was a predictor of mortality within 28 and 90 days.

CONCLUSION

Trace element deficiency in patients with alcoholic hepatitis is highly prevalent and associated with infection and mortality. Supplementation with selected trace elements may improve clinical outcomes in this patient group but further insight is required of their biological and clinical effects.

Bioinformatics of Metalloproteins and Metalloproteomes

Trace metals are inorganic elements that are required for all organisms in very low quantities. They serve as cofactors and activators of metalloproteins involved in a variety of key cellular processes. While substantial effort has been made in experimental characterization of metalloproteins and their functions, the application of bioinformatics in the research of metalloproteins and metalloproteomes is still limited. In the last few years, computational prediction and comparative genomics of metalloprotein genes have arisen, which provide significant insights into their distribution, function, and evolution in nature. This review aims to offer an overview of recent advances in bioinformatic analysis of metalloproteins, mainly focusing on metalloprotein prediction and the use of different metals across the tree of life. We describe current computational approaches for the identification of metalloprotein genes and metal-binding sites/patterns in proteins, and then introduce a set of related databases. Furthermore, we discuss the latest research progress in comparative genomics of several important metals in both prokaryotes and eukaryotes, which demonstrates divergent and dynamic evolutionary patterns of different metalloprotein families and metalloproteomes. Overall, bioinformatic studies of metalloproteins provide a foundation for systematic understanding of trace metal utilization in all three domains of life.

The bio-relevant metals of the periodic table of the elements

The bio-relevant metals (and derived compounds) of the Periodic Table of the Elements (PTE) are in the focus. The bulk elements sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) from the s-block, which are essential for all kingdoms of life, and some of their bio-activities are discussed. The trace elements of the d-block of the PTE as far as they are essential for humans (Mn, Fe, Co, Cu, Zn, Mo) are emphasized, but V, Ni, Cd, and W, which are essential only for some forms of life, are also considered. Chromium is no longer classified as being essential. From the p-block metals only the metalloid (half-metal) selenium (Se) is essential for all forms of life. Two other metalloids, silicon and arsenic, are briefly mentioned, but they have not been proven as being essential for humans. All metals of the PTE and a plethora of their compounds are used in industry and many of them are highly toxic, like lead (Pb), which is discussed as a prime example. Several metals of the PTE, that is, their ions and complexes, are employed in medicine and we discuss the role of lithium, gallium, strontium, technetium, silver, gadolinium (the only f-block element), platinum, and gold.

Comparative genomics and metagenomics of the metallomes

Recent achievements and advances in comparative genomic and metagenomic analyses of trace metals were reviewed and discussed.

Biology of the Gonococcus: Disease and Pathogenesis

Neisseria gonorrhoeae infection is a major public health problem worldwide. The increasing incidence of gonorrhea coupled with global spread of multidrug-resistant isolates of gonococci has ushered in an era of potentially untreatable infection. Gonococcal disease elicits limited immunity, and individuals are susceptible to repeated infections. In this chapter, we describe gonococcal disease and epidemiology and the structure and function of major surface components involved in pathogenesis. We also discuss the mechanisms that gonococci use to evade host immune responses and the immune responses following immunization with selected bacterial components that may overcome evasion. Understanding the biology of the gonococcus may aid in preventing the spread of gonorrhea and also facilitate the development of gonococcal vaccines and treatments.

Genome-wide identification, in silico characterization and expression analysis of ZIP-like genes from Trichomonas vaginalis in response to Zinc and Iron

Trace elements such as Zinc and Iron are essential components of metalloproteins and serve as cofactors or structural elements for enzymes involved in several important biological processes in almost all organisms. Because either excess or insufficient levels of Zn and Fe can be harmful for the cells, the homeostatic levels of these trace minerals must be tightly regulated. The Zinc regulated transporter, Iron regulated transporter-like Proteins (ZIP) comprise a diverse family, with several paralogues in diverse organisms and are considered essential for the Zn and Fe uptake and homeostasis. Zn and Fe has been shown to regulate expression of proteins involved in metabolism and pathogenicity mechanisms in the protozoan pathogen Trichomonas vaginalis, in contrast high concentrations of these elements were also found to be toxic for T. vaginalis trophozoites. Nevertheless, Zn and Fe uptake and homeostasis mechanisms is not yet clear in this parasite. We performed a genome-wide analysis and localized the 8 members of the ZIP gene family in T. vaginalis (TvZIP1-8). The bioinformatic programs predicted that the TvZIP proteins are highly conserved and show similar properties to the reported in other ZIP orthologues. The expression patterns of TvZIP1, 3, 5 and 7 were diminished in presence of Zinc, while the rest of the TvZIP genes showed an unchanged profile in this condition. In addition, TvZIP2 and TvZIP4 showed a differential expression pattern in trophozoites growth under different Iron conditions. These results suggest that TvZIP genes encode membrane transporters that may be responsible for the Zn and Fe acquisition in T. vaginalis.

Transition metals at the host-pathogen interface: how Neisseria exploit human metalloproteins for acquiring iron and zinc

Transition metals are essential nutrients for all organisms and important players in the host-microbe interaction. During bacterial infection, a tug-of-war between the host and microbe for nutrient metals occurs: the host innate immune system responds to the pathogen by reducing metal availability and the pathogen tries to outmaneuver this response. The outcome of this competition, which involves metal-sequestering host-defense proteins and microbial metal acquisition machinery, is an important determinant for whether infection occurs. One strategy bacterial pathogens employ to overcome metal restriction involves hijacking abundant host metalloproteins. The obligate human pathogens Neisseria meningitidis and N. gonorrhoeae express TonB-dependent transport systems that capture human metalloproteins, extract the bound metal ions, and deliver these nutrients into the bacterial cell. This review highlights structural and mechanistic investigations that provide insights into how Neisseria acquire iron from the Fe(III)-transport protein transferrin (TF), the Fe(III)-chelating host-defense protein lactoferrin (LF), and the oxygen-transport protein hemoglobin (Hb), and obtain zinc from the metal-sequestering antimicrobial protein calprotectin (CP).

Revisiting and re-engineering the classical zinc finger peptide: consensus peptide-1 (CP-1)

Zinc plays key structural and catalytic roles in biology. Structural zinc sites are often referred to as zinc finger (ZF) sites, and the classical ZF contains a Cys2His2 motif that is involved in coordinating Zn(II). An optimized Cys2His2 ZF, named consensus peptide 1 (CP-1), was identified more than 20 years ago using a limited set of sequenced proteins. We have reexamined the CP-1 sequence, using our current, much larger database of sequenced proteins that have been identified from high-throughput sequencing methods, and found the sequence to be largely unchanged. The CCHH ligand set of CP-1 was then altered to a CAHH motif to impart hydrolytic activity. This ligand set mimics the His2Cys ligand set of peptide deformylase (PDF), a hydrolytically active M(II)-centered (M = Zn or Fe) protein. The resultant peptide [CP-1(CAHH)] was evaluated for its ability to coordinate Zn(II) and Co(II) ions, adopt secondary structure, and promote hydrolysis. CP-1(CAHH) was found to coordinate Co(II) and Zn(II) and a pentacoordinate geometry for Co(II)-CP-1(CAHH) was implicated from UV-vis data. This suggests a His2Cys(H2O)2 environment at the metal center. The Zn(II)-bound CP-1(CAHH) was shown to adopt partial secondary structure by 1-D (1)H NMR spectroscopy. Both Zn(II)-CP-1(CAHH) and Co(II)-CP-1(CAHH) show good hydrolytic activity toward the test substrate 4-nitrophenyl acetate, exhibiting faster rates than most active synthetic Zn(II) complexes.

Inhibition of interleukin-1β-mediated interleukin-1 receptor-associated kinase 4 phosphorylation by zinc leads to repression of memory T helper type 17 response in humans

Zinc is an essential trace element that plays pivotal roles in multiple facets of the immune system. Besides its catalytic and structural roles, zinc also functions as an intracellular signalling molecule, and changes in zinc levels can cause both direct and indirect modulation of immune responses. Further, cytoplasmic levels of bioavailable zinc in immune cells are largely influenced by many extracellular stimuli. Here we provide evidence that zinc represses memory T helper type 17 responses in humans by inhibiting interleukin-1β (IL-1β)-mediated signal. In vitro zinc treatment of CD4(+) T cells in the presence of activated monocytes inhibited interferon-γ-producing cells and IL-17-producing cells, but not IL-4-producing cells. Of note, production of IL-17(+) cells from memory CD4(+) T cells, which is significantly up-regulated by lipopolysaccharide-stimulated monocytes, was preferentially repressed by zinc. Increased cytoplasmic zinc in T cells suppressed IL-1β signalling through repression of phosphorylation of IL-1 receptor-associated kinase 4 (IRAK4), so leading to an inhibitory effect on T helper type 17 responses facilitated by monocyte-derived IL-1β in humans. These findings suggest that extracellular zinc bioavailability may affect memory CD4(+) T-cell responses by modulating the zinc-mediated signalling pathway.

The Kinetic Response of the Proteome in A549 Cells Exposed to ZnSO4 Stress

Zinc, an essential trace element, is involved in many important physiological processes. Cell responses to zinc stress show time-dependent effects besides concentration-dependence and tissue-specificity. Herein, we investigated the time-dependent differential expression of the proteome in A549 cells after administered with ZnSO4 for both 9 and 24 h using 2DE. 123 differentially expressed protein spots were detected, most of which were up-regulated by Zn2+ treatment. Interestingly, 49 proteins exhibited significant differential expression repeatedly during these two treatment periods, and moreover showed a conserved change with different ratios and four time-dependent expression patterns. Pattern 1 (up-regulated with rapid initial induction and subsequent repression) and pattern 4 (down-regulated with steady repression) were the predominant expression patterns. The abundances of the proteins in patterns 1 and 4 after 24 h of zinc treatment are always lower than that after 9 h, indicating that exogenous zinc reduced the expression of proteins in cells after 24 h or longer. Importantly, these findings could also reflect the central challenge in detecting zinc homeostasis proteins by 2DE or other high throughput analytical methods resulting from slight variation in protein expression after certain durations of exogenous zinc treatment and/or low inherent protein content in cells. These time-dependent proteome expression patterns were further validated by measuring dynamic changes in protein content in cells and in expression of two proteins using the Bradford method and western blotting, respectively. The time-dependent changes in total zinc and free Zn2+ ion contents in cells were measured using ICP-MS and confocal microscopy, respectively. The kinetic process of zinc homeostasis regulated by muffling was further revealed. In addition, we identified 50 differentially expressed proteins which are predominantly involved in metabolic process, cellular process or developmental process, and function as binding, catalytic activity or structural molecule activity. This study further elucidates our understanding of dynamic nature of the cellular response to zinc stress and the mechanism of zinc homeostasis.

Selective Sensitization of Zinc Finger Protein Oxidation by Reactive Oxygen Species through Arsenic Binding

Cysteine oxidation induced by reactive oxygen species (ROS) on redox-sensitive targets such as zinc finger proteins plays a critical role in redox signaling and subsequent biological outcomes. We found that arsenic exposure led to oxidation of certain zinc finger proteins based on arsenic interaction with zinc finger motifs. Analysis of zinc finger proteins isolated from arsenic-exposed cells and zinc finger peptides by mass spectrometry demonstrated preferential oxidation of C3H1 and C4 zinc finger configurations. C2H2 zinc finger proteins that do not bind arsenic were not oxidized by arsenic-generated ROS in the cellular environment. The findings suggest that selectivity in arsenic binding to zinc fingers with three or more cysteines defines the target proteins for oxidation by ROS. This represents a novel mechanism of selective protein oxidation and demonstrates how an environmental factor may sensitize certain target proteins for oxidation, thus altering the oxidation profile and redox regulation.

Zinc and its role in immunity and inflammation

Zinc (Zn) nutritional importance has been known for a long time, but in the last decades its importance in immune modulation has arisen. This review aims at describing the mechanisms involved in the regulation of Zn homeostasis and their effects on the immune response focusing on those which are implicated in the physiopathology of rheumatoid arthritis. Zn functions as a modulator of the immune response through its availability, which is tightly regulated by several transporters and regulators. When this mechanism is disturbed, Zn availability is reduced, altering survival, proliferation and differentiation of the cells of different organs and systems and, in particular, cells of the immune system. Zn deficiency affects cells involved in both innate and adaptive immunity at the survival, proliferation and maturation levels. These cells include monocytes, polymorphonuclear-, natural killer-, T-, and B-cells. T cell functions and the balance between the different T helper cell subsets are particularly susceptible to changes in Zn status. While acute Zn deficiency causes a decrease in innate and adaptive immunity, chronic deficiency increases inflammation. During chronic deficiency, the production of pro-inflammatory cytokines increases, influencing the outcome of a large number of inflammatory diseases, including rheumatoid arthritis.

Addition of a second binding site increases the dynamic range but alters the cellular localization of a red fluorescent probe for mobile zinc

We report the synthesis and photophysical properties of ZBR4 and ZR1, two resorufin-based ditopic probes for mobile zinc. Upon binding Zn(2+), the sensors display 14- and 41-fold enhancements of their red fluorescence emission, respectively. In contrast to ZR1 and other members of the ZBR family, which accumulate in the endoplasmic reticulum, ZBR4 spontaneously localizes to the mitochondria of HeLa cells. The modular approach in designing the constructs facilitates a homologation strategy aimed at tuning the zinc-binding and intracellular targeting properties of future probes.

SpiroZin1: a reversible and pH-Insensitive, reaction-based, red-fluorescent probe for imaging biological mobile zinc

A reversible, reaction-based sensor for biological mobile zinc was designed, prepared, and characterized. The sensing mechanism of this probe is based on the zinc-induced, ring-opening reaction of spirobenzopyran to give a cyanine fluorophore that emits in the deep-red region of the electromagnetic spectrum. This probe is not activated by protons and operates efficiently in aqueous solution at pH 7 and high ionic strength. The mechanism of this reaction was studied by using a combination of kinetics experiments and DFT calculations. The biocompatibility of the probe was demonstrated in live HeLa cells.

New insights into histidine triad proteins: solution structure of a Streptococcus pneumoniae PhtD domain and zinc transfer to AdcAII

Zinc (Zn²⁺) homeostasis is critical for pathogen host colonization and invasion. Polyhistidine triad (Pht) proteins, located at the surface of various streptococci, have been proposed to be involved in Zn²⁺ homeostasis. The phtD gene, coding for a Zn²⁺-binding protein, is organized in an operon with adcAII coding for the extracellular part of a Zn²⁺ transporter. In the present work, we investigate the relationship between PhtD and AdcAII using biochemical and structural biology approaches. Immuno-precipitation experiments on purified membranes of Streptococcus pneumoniae (S. pneumoniae) demonstrate that native PhtD and AdcAII interact in vivo confirming our previous in vitro observations. NMR was used to demonstrate Zn²⁺ transfer from the Zn²⁺-bound form of a 137 amino acid N-terminal domain of PhtD (t-PhtD) to AdcAII. The high resolution NMR structure of t-PhtD shows that Zn²⁺ is bound in a tetrahedral site by histidines 83, 86, and 88 as well as by glutamate 63. Comparison of the NMR parameters measured for apo- and Zn²⁺-t-PhtD shows that the loss of Zn²⁺ leads to a diminished helical propensity at the C-terminus and increases the local dynamics and overall molecular volume. Structural comparison with the crystal structure of a 55-long fragment of PhtA suggests that Pht proteins are built from short repetitive units formed by three β-strands containing the conserved HxxHxH motif. Taken together, these results support a role for S. pneumoniae PhtD as a Zn²⁺ scavenger for later release to the surface transporter AdcAII, leading to Zn²⁺ uptake.

The zinc transporter Zip5 (Slc39a5) regulates intestinal zinc excretion and protects the pancreas against zinc toxicity

Background

ZIP5 localizes to the baso-lateral membranes of intestinal enterocytes and pancreatic acinar cells and is internalized and degraded coordinately in these cell-types during periods of dietary zinc deficiency. These cell-types are thought to control zinc excretion from the body. The baso-lateral localization and zinc-regulation of ZIP5 in these cells are unique among the 14 members of the Slc39a family and suggest that ZIP5 plays a role in zinc excretion.

Methods/Principal Findings

We created mice with floxed Zip5 genes and deleted this gene in the entire mouse or specifically in enterocytes or acinar cells and then examined the effects on zinc homeostasis. We found that ZIP5 is not essential for growth and viability but total knockout of ZIP5 led to increased zinc in the liver in mice fed a zinc-adequate (ZnA) diet but impaired accumulation of pancreatic zinc in mice fed a zinc-excess (ZnE) diet. Loss-of-function of enterocyte ZIP5, in contrast, led to increased pancreatic zinc in mice fed a ZnA diet and increased abundance of intestinal Zip4 mRNA. Finally, loss-of-function of acinar cell ZIP5 modestly reduced pancreatic zinc in mice fed a ZnA diet but did not impair zinc uptake as measured by the rapid accumulation of ⁶⁷zinc. Retention of pancreatic ⁶⁷zinc was impaired in these mice but the absence of pancreatic ZIP5 sensitized them to zinc-induced pancreatitis and exacerbated the formation of large cytoplasmic vacuoles containing secretory protein in acinar cells.

Conclusions

These studies demonstrate that ZIP5 participates in the control of zinc excretion in mice. Specifically, they reveal a paramount function of intestinal ZIP5 in zinc excretion but suggest a role for pancreatic ZIP5 in zinc accumulation/retention in acinar cells. ZIP5 functions in acinar cells to protect against zinc-induced acute pancreatitis and attenuate the process of zymophagy. This suggests that it may play a role in autophagy.

A recessive X-linked mutation causes a threefold reduction of total body zinc accumulation in Drosophila melanogaster laboratory strains

A newly identified human locus on chromosome 15 was recently associated with zinc accumulation. Based on a prior report of a threefold difference in zinc accumulation between fumble¹ heterozygous mutants and control fly strains, it was suggested that phosphopantothenoylcysteine decarboxylase might affect zinc status through its effects on vitamin B5 (pantothenate) metabolism. We report here that outcrossed fumble¹ heterozygous mutant flies with low zinc content have been recovered, suggesting that pantothenate metabolism did not alter zinc homeostasis in fumble¹ heterozygous flies. We show instead that the Drosophila condition of low body zinc accumulation is an X-chromosome-linked recessive trait.

•

Flies with a threefold reduction in zinc accumulation remain viable and fertile.

•

There is no causal association between zinc accumulation and fly pantothenate kinase mutants.

•

A widespread X-linked mutation causes a threefold reduction in zinc accumulation in Drosophila.

Zinc biochemistry: from a single zinc enzyme to a key element of life

The nutritional essentiality of zinc for the growth of living organisms had been recognized long before zinc biochemistry began with the discovery of zinc in carbonic anhydrase in 1939. Painstaking analytical work then demonstrated the presence of zinc as a catalytic and structural cofactor in a few hundred enzymes. In the 1980s, the field again gained momentum with the new principle of "zinc finger" proteins, in which zinc has structural functions in domains that interact with other biomolecules. Advances in structural biology and a rapid increase in the availability of gene/protein databases now made it possible to predict zinc-binding sites from metal-binding motifs detected in sequences. This procedure resulted in the definition of zinc proteomes and the remarkable estimate that the human genome encodes ∼3000 zinc proteins. More recent developments focus on the regulatory functions of zinc(II) ions in intra- and intercellular information transfer and have tantalizing implications for yet additional functions of zinc in signal transduction and cellular control. At least three dozen proteins homeostatically control the vesicular storage and subcellular distribution of zinc and the concentrations of zinc(II) ions. Novel principles emerge from quantitative investigations on how strongly zinc interacts with proteins and how it is buffered to control the remarkably low cellular and subcellular concentrations of free zinc(II) ions. It is fair to conclude that the impact of zinc for health and disease will be at least as far-reaching as that of iron.