Copper transport activity of yeast Ctr1 is down-regulated via its C terminus in response to excess copper

Characterization of a High-Affinity Copper Transporter in the White-Nose Syndrome Causing Fungal Pathogen Pseudogymnoascus destructans

Copper is an essential micronutrient and the ability to scavenge tightly bound or trace levels of copper ions at the host-pathogen interface is vital for fungal proliferation in animal hosts. Recent studies suggest that trace metal ion acquisition is critical for the establishment and propagation of Pseudogymnoascus destructans , the fungal pathogen responsible for white-nose syndrome (WNS), on their bat host. However, little is known about these metal acquisition pathways in P. destructans . In this study, we report the characterization of the P. destructans high-affinity copper transporter VC83_00191 ( Pd CTR1a), which is implicated as a virulence factor associated with the WNS disease state. Using Saccharomyces cerevisiae as a recombinant expression host, we find that Pd CTR1a localizes to the cell surface plasma membrane and can efficiently traffic Cu-ions into the yeast cytoplasm. Complementary studies in the native P. destructans fungus provide evidence that Pd CTR1a transcripts and protein levels are dictated by Cu-bioavailability in the growth media. Our study demonstrates that Pd CTR1a is a functional high-affinity copper transporter and is relevant to Cu-homeostasis pathways in P. destructans .

A novel method of rapid detection for heavy metal copper ion via a specific copper chelator bathocuproinedisulfonic acid disodium salt

The extensive usage and production of copper may lead to toxic effects in organisms due to its accumulation in the environment. Traditional methods for copper detection are time consuming and infeasible for field usage. It is necessary to discover a real-time, rapid and economical method for detecting copper to ensure human health and environmental safety. Here we developed a colorimetric paper strip method and optimized spectrum method for rapid detection of copper ion based on the specific copper chelator bathocuproinedisulfonic acid disodium salt (BCS). Both biological assays and chemical methods verified the specificity of BCS for copper. The optimized reaction conditions were 50 mM Tris-HCl pH 7.4, 200 µM BCS, 1 mM ascorbate and less than 50 µM copper. The detection limit of the copper paper strip test was 0.5 mg/L by direct visual observation and the detection time was less than 1 min. The detection results of grape, peach, apple, spinach and cabbage by the optimized spectrum method were 0.91 μg/g, 0.87 μg/g, 0.19 μg/g, 1.37 μg/g and 0.39 μg/g, respectively. The paper strip assays showed that the copper contents of grape, peach, apple, spinach and cabbage were 0.8 mg/L, 0.9 mg/L, 0.2 mg/L, 1.3 mg/L and 0.5 mg/L, respectively. These results correlated well with those determined by inductively coupled plasma-mass spectrometry (ICP-MS). The visual detection limit of the paper strip based on Cu-BCS-AgNPs was 0.06 mg/L. Our study demonstrates the potential for on-site, rapid and cost-effective copper monitoring of foods and the environment.

Toxicity and assimilation of cellulosic copper nanoparticles require α-arrestins in S. cerevisiae

The increased use of antimicrobial compounds such as copper into nanoparticles changes how living cells interact with these novel materials. The increased use of antimicrobial nanomaterials combats infectious disease and food spoilage. Fungal infections are particularly difficult to treat because of the few druggable targets, and Saccharomyces cerevisiae provides an insightful model organism to test these new materials. However, because of the novel characteristics of these materials, it is unclear how these materials interact with living cells and if resistance to copper-based nanomaterials could occur. Copper nanoparticles built on carboxymethylcellulose microfibril strands with copper (CMC-Cu) are a promising nanomaterial when imported into yeast cells and induce cell death. The α-arrestins are cargo adaptors that select which molecules are imported into eukaryotic cells. We screened α-arrestins mutants and identified Aly2, Rim8, and Rog3 α-arrestins, which are necessary for the internalization of CMC-Cu nanoparticles. Internal reactive oxygen species in these mutants were lower and corresponded to the increased viability in the presence of CMC-Cu. Using lattice light-sheet microscopy on live cells, we determined that CMC-Cu were imported into yeast within 30 min of exposure. Initially, the cytoplasmic pH decreased but returned to basal level 90 min later. However, there was heterogeneity in response to CMC-Cu exposure, which could be due to the heterogeneity of the particles or differences in the metabolic states within the population. When yeast were exposed to sublethal concentrations of CMC-Cu no resistance occurred. Internalization of CMC-Cu increases the potency of these antimicrobial nanomaterials and is likely key to preventing fungi from evolving resistance.

Structure-activity assessment of flavonoids as modulators of copper transport

Flavonoids are polyphenolic small molecules that are abundant in plant products and are largely recognized for their beneficial health effects. Possessing both antioxidant and prooxidant properties, flavonoids have complex behavior in biological systems. The presented work investigates the intersection between the biological activity of flavonoids and their interactions with copper ions. Copper is required for the proper functioning of biological systems. As such, dysregulation of copper is associated with metabolic disease states such as diabetes and Wilson's disease. There is evidence that flavonoids bind copper ions, but the biological implications of their interactions remain unclear. Better understanding these interactions will provide insight into the mechanisms of flavonoids' biological behavior and can inform potential therapeutic targets. We employed a variety of spectroscopic techniques to study flavonoid-Cu(II) binding and radical scavenging activities. We identified structural moieties important in flavonoid-copper interactions which relate to ring substitution but not the traditional structural subclassifications. The biological effects of the investigated flavonoids specifically on copper trafficking were assessed in knockout yeast models as well as in human hepatocytes. The copper modulating abilities of strong copper-binding flavonoids were largely influenced by the relative hydrophobicities. Combined, these spectroscopic and biological data help elucidate the intricate nature of flavonoids in affecting copper transport and open avenues to inform dietary recommendations and therapeutic development.

Copper chelation therapy inhibits renal fibrosis by modulating copper transport proteins

The copper (Cu) transporter proteins play an important role in the maintenance of the Cu homeostasis in the body. Lysyl oxidase (LOX) proteins are involved in crosslinking of collagens and elastin molecules resulting in the establishment of extracellular matrix (ECM) and require Cu for their functional activity. Although there are few reports showing the protective effects of Cu chelators, the mechanism behind protection remains unknown. The present study investigated the role of Cu transporter proteins in renal fibrosis. We used tubular epithelial cells and three different animal models of renal injury to investigate the induction of Cu transporter proteins in renal injury with different etiology. We used disulfiram, clioquinol as two Cu chelators and ammonium tetrathiomolybdate as a standard Cu chelator. In addition, β-aminopropionitrile (BAPN) was used as a standard LOX inhibitor. We demonstrated that renal fibrosis is associated with the induction of Cu transporter proteins such as ATP7A and Copper Transporter 1 (CTR1) but the Cu overload did not induce renal fibrosis. In addition, the Cu chelators inhibited renal fibrosis by inhibiting the Cu transporter proteins.

Heterologous Expression of Full-Length and Truncated Human ZIP4 Zinc Transporter in Saccharomyces cerevisiae

The human (h) transporter hZIP4 is the primary Zn²⁺ importer in the intestine. hZIP4 is also expressed in a variety of organs such as the pancreas and brain. Dysfunction of hZIP4 can result in the Zn²⁺ deficiency disease acrodermatitis enteropathica (AE). AE can disrupt digestive and immune system homeostasis. A limited number of hZIP4 expression strategies have hindered increasing knowledge about this essential transmembrane protein. Here, we report the heterologous expression of hZIP4 in Saccharomyces cerevisiae. Both a wild-type and a mutant S. cerevisiae strain, in which the endogenous Zn²⁺ transporters were deleted, were used to test the expression and localization of an hZIP4–GFP fusion protein. A full-length hZIP4–GFP and a truncated membrane-domain-only (mhZIP4–GFP) protein were observed to be present in the plasma membrane in yeast.

Heavy metal transporters: Functional mechanisms, regulation, and application in phytoremediation

Heavy metal pollution in soil is a global problem with serious impacts on human health and ecological security. Phytoextraction in phytoremediation, in which plants uptake and transport heavy metals (HMs) to the tissues of aerial parts, is the most environmentally friendly method to reduce the total amount of HMs in soil and has wide application prospects. However, the molecular mechanism of phytoextraction is still under investigation. The uptake, translocation, and retention of HMs in plants are mainly mediated by a variety of transporter proteins. A better understanding of the accumulation strategy of HMs via transporters in plants is a prerequisite for the improvement of phytoextraction. In this review, the biochemical structure and functions of HM transporter families in plants are systematically summarized, with emphasis on their roles in phytoremediation. The accumulation mechanism and regulatory pathways related to hormones, regulators, and reactive oxygen species (ROS) of HMs concerning these transporters are described in detail. Scientific efforts and practices for phytoremediation carried out in recent years suggest that creation of hyperaccumulators by transgenic or gene editing techniques targeted to these transporters and their regulators is the ultimate powerful path for the phytoremediation of HM contaminated soils.

Copper(II) import and reduction are dependent on His-Met clusters in the extracellular amino terminus of human copper transporter-1

Copper(I) is an essential metal for all life forms. Though Cu(II) is the most abundant and stable state, its reduction to Cu(I) via an unclear mechanism is prerequisite for its bioutilization. In eukaryotes, the copper transporter-1 (CTR1) is the primary high-affinity copper importer, although its mechanism and role in Cu(II) reduction remain uncharacterized. Here we show that extracellular amino-terminus of human CTR1 contains two methionine-histidine clusters and neighboring aspartates that distinctly bind Cu(I) and Cu(II) preceding its import. We determined that hCTR1 localizes at the basolateral membrane of polarized MDCK-II cells and that its endocytosis to Common-Recycling-Endosomes is regulated by reduction of Cu(II) to Cu(I) and subsequent Cu(I) coordination by the methionine cluster. We demonstrate the transient binding of both Cu(II) and Cu(I) during the reduction process is facilitated by aspartates that also act as another crucial determinant of hCTR1 endocytosis. Mutating the first Methionine cluster (⁷Met-Gly-Met⁹) and Asp¹³ abrogated copper uptake and endocytosis upon copper treatment. This phenotype could be reverted by treating the cells with reduced and nonreoxidizable Cu(I). We show that histidine clusters, on other hand, bind Cu(II) and are crucial for hCTR1 functioning at limiting copper. Finally, we show that two N-terminal His-Met-Asp clusters exhibit functional complementarity, as the second cluster is sufficient to preserve copper-induced CTR1 endocytosis upon complete deletion of the first cluster. We propose a novel and detailed mechanism by which the two His-Met-Asp residues of hCTR1 amino-terminus not only bind copper, but also maintain its reduced state, crucial for intracellular uptake.

Identification and molecular characterization of the high-affinity copper transporters family in Solanum lycopersicum

Copper (Cu) plays a key role as cofactor in the plant proteins participating in essential cellular processes, such as electron transport and free radical scavenging. Despite high-affinity Cu transporters (COPTs) being key participants in Cu homeostasis maintenance, very little is known about COPTs in tomato (Solanum lycopersicum) even though it is the most consumed fruit worldwide and this crop is susceptible to suboptimal Cu conditions. In this study, a six-member family of COPT (SlCOPT1-6) was identified and characterized. SlCOPTs have a conserved architecture consisting of three transmembrane domains and β-strains. However, the presence of essential methionine residues, a methionine-enriched amino-terminal region, an Mx₃Mx₁₂Gx₃G Cu-binding motif and a cysteine rich carboxy-terminal region, all required for their functionality, is more variable among members. Accordingly, functional complementation assays in yeast indicate that SlCOPT1 and SlCOPT2 are able to transport Cu inside the cell, while SlCOPT3 and SlCOPT5 are only partially functional. In addition, protein interaction network analyses reveal the connection between SlCOPTs and Cu P_IB-type ATPases, other metal transporters, and proteins related to the peroxisome. Gene expression analyses uncover organ-dependency, fruit vasculature tissue specialization and ripening-dependent gene expression profiles, as well as different response to Cu deficiency or toxicity in an organ-dependent manner.

A differential subcellular localization of two copper transporters from the COPT family suggests distinct roles in copper homeostasis in Physcomitrium patens

The moss Physcomitrium (Physcomitrella) patens is a bryophyte that provides genetic information about the adaptation to the life on land by early Embryophytes and is a reference organism for comparative evolutionary studies in plants. Copper is an essential micronutrient for every living organism, its transport across the plasma membrane is achieved by the copper transport protein family COPT/CTR. Two genes related to the COPT family were identified in Physcomitrella patens, PpaCOPT1 and PpaCOPT2. Homology modelling of both proteins showed the presence of three putative transmembrane domains (TMD) and the Mx₃M motif, constituting a potential Cu ⁺ selectivity filter present in other members of this family. Functional characterization of PpaCOPT1 and PpaCOPT2 in the yeast mutant ctr1Δctr3Δ restored its growth on medium with non-fermentable carbon sources at micromolar Cu concentrations, providing support that these two moss proteins function as high affinity Cu ⁺ transporters. Localization of PpaCOPT1 and PpaCOPT2 in yeast cells was observed at the tonoplast and plasma membrane, respectively. The heterologous expression of PpaCOPT2 in tobacco epidermal cells co-localized with the plasma membrane marker. Finally, only PpaCOPT1 was expressed in seven-day old protonema and was influenced by extracellular copper levels. This evidence suggests different roles of PpaCOPT1 and PpaCOPT2 in copper homeostasis in Physcomitrella patens.

MTM1 plays an important role in the regulation of zinc tolerance in Saccharomyces cerevisiae

BACKGROUND

Acquisition and distribution of zinc supports a number of biological processes. Various molecular factors are involved in zinc metabolism but not fully explored.

BASIC PROCEDURES

Spontaneous mutants were generated in yeast with excess zinc culture followed by whole genome DNA sequencing to discover zinc metabolism related genes by bioinformatics. An identified mutant was characterized through metallomic and molecular biology methods.

MAIN FINDINGS

Here we reported that MTM1 knockout cells displayed much stronger zinc tolerance than wild type cells on SC medium when exposed to excess zinc. Zn accumulation of mtm1Δ cells was dramatically decreased compared to wild type cells under excessive zinc condition due to MTM1 deletion reduced zinc uptake. ZRC1 mRNA level of mtm1Δ cells was significantly higher than that in the wild-type strain leading to increased vacuolar zinc accumulations in mtm1Δ cells. The mRNA levels of ZRT1 and ZAP1 decreased in mtm1Δ cells contributing to less Zn uptake. The zrc1Δmtm1Δ double knockout strain exhibited Zn sensitivity. MTM1 knockout did not afford resistance to excess zinc through an effect mediated through an influence on levels of ROS. Superoxide dismutase 2 (Sod2p) activity in mtm1Δ cells was severely impaired and not restored through Zn supplementation. Meanwhile, additional Zn showed no significant effect on the localization and expression of Mtm1p.

PRINCIPAL CONCLUSIONS

Our study reveals the MTM1 gene plays an important role in the regulation of zinc homeostasis in yeast cells via changing zinc uptake and distribution. This discovery provides new insights for better understanding biochemical communication between vacuole and mitochondrial in relation to zinc-metabolism.

Superoxide Dismutase 1 in Health and Disease: How a Frontline Antioxidant Becomes Neurotoxic

Cu/Zn superoxide dismutase (SOD1) is a frontline antioxidant enzyme catalysing superoxide breakdown and is important for most forms of eukaryotic life. The evolution of aerobic respiration by mitochondria increased cellular production of superoxide, resulting in an increased reliance upon SOD1. Consistent with the importance of SOD1 for cellular health, many human diseases of the central nervous system involve perturbations in SOD1 biology. But far from providing a simple demonstration of how disease arises from SOD1 loss-of-function, attempts to elucidate pathways by which atypical SOD1 biology leads to neurodegeneration have revealed unexpectedly complex molecular characteristics delineating healthy, functional SOD1 protein from that which likely contributes to central nervous system disease. This review summarises current understanding of SOD1 biology from SOD1 genetics through to protein function and stability.

Molecular characterization of the COPT/Ctr-type copper transporter family under heavy metal stress in alfalfa

In nature, heavy metals significantly affect crop growth and quality. Among various heavy metals, copper (Cu) is both essential and toxic to plants depending on the concentration and complex homeostatic networks. The Cu transporter family (COPT) plays important roles in Cu homeostasis, including absorption, transportation, and growth in plants; however, this gene family is still poorly understood in alfalfa (Medicago sativa L.). In this study, a total of 12 MsCOPTs were identified and characterized. Based on the conserved motif and phylogenetic analysis, MsCOPTs could be divided into four subgroups (A1, A2, A3, and B). Gene structure, chromosomal location, and synteny analyses of MsCOPTs showed that segmental and tandem duplications likely contributed to their evolution. Tissue-specific expression analysis of MsCOPT genes indicated diverse spatiotemporal expression patterns. Most MsCOPT genes had high transcription levels in roots and nodules, indicating that these genes may play vital roles in the absorption and transport of Cu through root. The complementary heterologous expression function of yeast once again indicates that root-specific COPT can supplement the growth of defective yeast strains on YPEG medium, suggesting that these genes are Cu transporters. In summary, for the first time, our research identified COPT family genes at the whole-genome level to provide guidance for effectively improving the problem of Cu deficiency in the grass-livestock chain and provide theoretical support for the subsequent development of grass and animal husbandry.

Endocytosis of nutrient transporters in fungi: The ART of connecting signaling and trafficking

Plasma membrane transporters play pivotal roles in the import of nutrients, including sugars, amino acids, nucleobases, carboxylic acids, and metal ions, that surround fungal cells. The selective removal of these transporters by endocytosis is one of the most important regulatory mechanisms that ensures a rapid adaptation of cells to the changing environment (e.g., nutrient fluctuations or different stresses). At the heart of this mechanism lies a network of proteins that includes the arrestin‐related trafficking adaptors (ARTs) which link the ubiquitin ligase Rsp5 to nutrient transporters and endocytic factors. Transporter conformational changes, as well as dynamic interactions between its cytosolic termini/loops and with lipids of the plasma membrane, are also critical during the endocytic process. Here, we review the current knowledge and recent findings on the molecular mechanisms involved in nutrient transporter endocytosis, both in the budding yeast Saccharomyces cerevisiae and in some species of the filamentous fungus Aspergillus. We elaborate on the physiological importance of tightly regulated endocytosis for cellular fitness under dynamic conditions found in nature and highlight how further understanding and engineering of this process is essential to maximize titer, rate and yield (TRY)-values of engineered cell factories in industrial biotechnological processes.

A novel assessment system of toxicity and stability of CuO nanoparticles via copper super sensitive Saccharomyces cerevisiae mutants

CuO nanoparticles (CuO-NPs) toxicity in organisms is contributed mainly through the copper uptake by both the ionic and nanoparticle form. However, the relative uptake ratio and bioavailability of the two different forms is not well known due to a lack of sensitive and effective assessment systems. We developed a series of both copper resistant and hyper sensitive Saccharomyces cerevisiae mutants to investigate and compare the effects of CuO-NPs and dissolved copper (CuCl₂), on the eukaryote with the purpose of quantitating the relative contributions of nanoparticles and dissolved species for Cu uptake. We observed the toxicity of 10 mM CuO-NPs for copper sensitive strains is equal to that of 0.5 mM CuCl₂ and the main toxic effect is most likely generated from oxidative stress through reactive oxygen species (ROS) production. About 95% CuO-NPs exist in nanoparticle form under neutral environmental conditions. Assessing the cellular metal content of wild type and copper transporter 1(CTR1) knock out cells showed that endocytosis is the major absorption style for CuO-NPs. This study also found a similar toxicity of Ag for both 10 mM Ag-NPs and 0.2 mM AgNO₃ in the copper super sensitive strains. Our study revealed the absorption mechanism of soluble metal based nanomaterials CuO-NPs and Ag-NPs as well as provided a sensitive and delicate system to precisely evaluate the toxicity and stability of nanoparticles.

Copper Homeostasis in Aspergillus nidulans Involves Coordinated Transporter Function, Expression and Cellular Dynamics

Copper ion homeostasis involves a finely tuned and complex multi-level response system. This study expands on various aspects of the system in the model filamentous fungus Aspergillus nidulans. An RNA-seq screen in standard growth and copper toxicity conditions revealed expression changes in key copper response elements, providing an insight into their coordinated functions. The same study allowed for the deeper characterization of the two high-affinity copper transporters: AnCtrA and AnCtrC. In mild copper deficiency conditions, the null mutant of AnctrC resulted in secondary level copper limitation effects, while deletion of AnctrA resulted in primary level copper limitation effects under extreme copper scarcity conditions. Each transporter followed a characteristic expression and cellular localization pattern. Although both proteins partially localized at the plasma membrane, AnCtrC was visible at membranes that resembled the ER, whilst a substantial pool of AnCtrA accumulated in vesicular structures resembling endosomes. Altogether, our results support the view that AnCtrC plays a major role in covering the nutritional copper requirements and AnCtrA acts as a specific transporter for extreme copper deficiency scenarios.

Arabidopsis COPPER TRANSPORTER 1 undergoes degradation in a proteasome-dependent manner

The essential nutrient copper is toxic in excess. Therefore, plants must tightly control copper uptake and distribution. Arabidopsis thaliana high-affinity copper transporters (COPTs) mediate copper uptake, partitioning, and redistribution. Here we show that COPT1 localizes to the plasma membrane and endoplasmic reticulum in stably transgenic plants expressing a COPT1-green fluorescent protein (GFP) fusion protein, and the fusion protein is rapidly degraded upon plant exposure to excess copper. MG132 treatment largely abolished copper-induced degradation of COPT1, implying a link between the proteasome and COPT1 activity in modulating copper uptake. Co-immunoprecipitation analyses revealed that COPT1 cannot be ubiquitinated in the presence of excess copper and MG132. Through site-directed mutagenesis, we identified Lys159 in the C-terminal cytoplasmic tail of COPT1 as critical for copper acquisition, but not for copper-mediated down-regulation of COPT1, in plants. Furthermore, pharmacological analysis showed that treatment with a vesicle trafficking inhibitor or a V-ATPase inhibitor does not alter the subcellular dynamics of COPT1-GFP, consistent with the absence of a connection between the endosomal recycling/vacuolar system and COPT1 degradation. Together, our data suggest that proteasomal degradation rather than vacuolar proteolysis is important for the regulation of copper transport to maintain copper homeostasis in plants.

Structural and Functional Diversity Among the Members of CTR, the Membrane Copper Transporter Family

Copper is crucial for carrying out normal physiological functions in all higher life forms. Copper Transporter 1 (CTR1) is the high-affinity copper importer found in all eukaryotic organisms. The copper transporter family primarily comprises ~ six members (CTR1-6) and the related members share high sequence homology with CTR. However, with the exception of CTR1, not all six CTRs are present in every organism. Despite having a simple trimeric channel structure, CTR1 and other members exhibit some unique regulatory properties. In the present review, we attempt to understand the diversity and similarity of regulation and functioning of the members of this copper transporter family.

Roles for intracellular cation transporters in respiratory growth of yeast

Potassium is involved in copper and iron metabolism in eukaryotic Golgi apparatus, but it is not clear yet whether potassium distributions in other vesicles also affect copper and iron metabolism. Here we show that respiratory growth and iron acquisition by the yeast Saccharomyces cerevisiae relies on potassium (K+) compartmentalization to the mitochondria, as well as the vacuole and late endosome via K+/H+ exchangers Mdm38p, Vnx1p and Nhx1p, respectively. The data indicate that NHX1 and VNX1 knock-out cells grow better than wild type cells on non-fermentable YPEG media, while MDM38 knock-out cells display a growth defect on YPEG media. The over expression of the KHA1 gene located on the Golgi apparatus partially compensates for the growth defect of the MDM38 knock-out strain. The results suggest that the vacuole and late endosome are important potassium storage vesicles and Mdm38p affects the mitochondrial function by regulating copper and iron metabolism. Our study reveals potassium compartmentalization to the subcellular vesicles is relevant for respiratory growth by improving copper utilization and promoting iron absorption.

Characterization of the Copper Transporters from Lotus spp. and Their Involvement under Flooding Conditions

Forage legumes are an important livestock nutritional resource, which includes essential metals, such as copper. Particularly, the high prevalence of hypocuprosis causes important economic losses to Argentinian cattle agrosystems. Copper deficiency in cattle is partially due to its low content in forage produced by natural grassland, and is exacerbated by flooding conditions. Previous results indicated that incorporation of Lotus spp. into natural grassland increases forage nutritional quality, including higher copper levels. However, the biological processes and molecular mechanisms involved in copper uptake by Lotus spp. remain poorly understood. Here, we identify four genes that encode putative members of the Lotus copper transporter family, denoted COPT in higher plants. A heterologous functional complementation assay of the Saccharomyces cerevisiae ctr1∆ctr3∆ strain, which lacks the corresponding yeast copper transporters, with the putative Lotus COPT proteins shows a partial rescue of the yeast phenotypes in restrictive media. Under partial submergence conditions, the copper content of L. japonicus plants decreases and the expression of two Lotus COPT genes is induced. These results strongly suggest that the Lotus COPT proteins identified in this work function in copper uptake. In addition, the fact that environmental conditions affect the expression of certain COPT genes supports their involvement in adaptive mechanisms and envisages putative biotechnological strategies to improve cattle copper nutrition.

The Rhizophagus irregularis Genome Encodes Two CTR Copper Transporters That Mediate Cu Import Into the Cytosol and a CTR-Like Protein Likely Involved in Copper Tolerance

Arbuscular mycorrhizal fungi increase fitness of their host plants under Cu deficient and toxic conditions. In this study, we have characterized two Cu transporters of the CTR family (RiCTR1 and RiCTR2) and a CTR-like protein (RiCTR3A) of Rhizophagus irregularis. Functional analyses in yeast revealed that RiCTR1 encodes a plasma membrane Cu transporter, RiCTR2 a vacuolar Cu transporter and RiCTR3A a plasma membrane protein involved in Cu tolerance. RiCTR1 was more highly expressed in the extraradical mycelia (ERM) and RiCTR2 in the intraradical mycelia (IRM). In the ERM, RiCTR1 expression was up-regulated by Cu deficiency and down-regulated by Cu toxicity. RiCTR2 expression increased only in the ERM grown under severe Cu-deficient conditions. These data suggest that RiCTR1 is involved in Cu uptake by the ERM and RiCTR2 in mobilization of vacuolar Cu stores. Cu deficiency decreased mycorrhizal colonization and arbuscule frequency, but increased RiCTR1 and RiCTR2 expression in the IRM, which suggest that the IRM has a high Cu demand. The two alternatively spliced products of RiCTR3, RiCTR3A and RiCTR3B, were more highly expressed in the ERM. Up-regulation of RiCTR3A by Cu toxicity and the yeast complementation assays suggest that RiCTR3A might function as a Cu receptor involved in Cu tolerance.

Identification and functional characterization of the ZmCOPT copper transporter family in maize

Copper (Cu) is an essential micronutrient for plant growth and development; Cu homeostasis in plant is maintained by the important functions of Ctr/COPT-type Cu transporters. Although the COPT genes have been identified in Arabidopsis thaliana and rice, little is known about Cu transporters in maize. In this study, three-members of putative maize Cu transporters (ZmCOPT 1, 2 and 3) are identified. ZmCOPT genes have expression in all of the tested tissues, including roots, stems, leaves and flowers (male and female), and their expression levels vary responding to stress due to Cu-deficiency and excess. Functional complementation and overexpression together with Cu uptake measurements in ZmCOPTs-transformed ctr1⊿ctr2⊿mutant strain or the wild type strain of Saccharomyces cerevisiae show that the three ZmCOPT members possess the ability to be Cu transporters. Among these, ZmCOPT1 and ZmCOPT2 have high-affinity while ZmCOPT3 has low-affinity. In addition, ZmCOPT2 tend to specifically transport Cu (I) but no other bivalent metal ions.

CHCA-1 is a copper-regulated CTR1 homolog required for normal development, copper accumulation, and copper-sensing behavior in Caenorhabditis elegans

Copper plays key roles in catalytic and regulatory biochemical reactions essential for normal growth, development, and health. Dietary copper deficiencies or mutations in copper homeostasis genes can lead to abnormal musculoskeletal development, cognitive disorders, and poor growth. In yeast and mammals, copper is acquired through the activities of the CTR1 family of high-affinity copper transporters. However, the mechanisms of systemic responses to dietary or tissue-specific copper deficiency remain unclear. Here, taking advantage of the animal model Caenorhabditis elegans for studying whole-body copper homeostasis, we investigated the role of a C. elegans CTR1 homolog, CHCA-1, in copper acquisition and in worm growth, development, and behavior. Using sequence homology searches, we identified 10 potential orthologs to mammalian CTR1 Among these genes, we found that chca-1, which is transcriptionally up-regulated in the intestine and hypodermis of C. elegans during copper deficiency, is required for normal growth, reproduction, and maintenance of systemic copper balance under copper deprivation. The intestinal copper transporter CUA-1 normally traffics to endosomes to sequester excess copper, and we found here that loss of chca-1 caused CUA-1 to mislocalize to the basolateral membrane under copper overload conditions. Moreover, animals lacking chca-1 exhibited significantly reduced copper avoidance behavior in response to toxic copper conditions compared with WT worms. These results establish that CHCA-1-mediated copper acquisition in C. elegans is crucial for normal growth, development, and copper-sensing behavior.

Metals in fungal virulence

Metals are essential for life, and they play a central role in the struggle between infecting microbes and their hosts. In fact, an important aspect of microbial pathogenesis is the 'nutritional immunity', in which metals are actively restricted (or, in an extended definition of the term, locally enriched) by the host to hinder microbial growth and virulence. Consequently, fungi have evolved often complex regulatory networks, uptake and detoxification systems for essential metals such as iron, zinc, copper, nickel and manganese. These systems often differ fundamentally from their bacterial counterparts, but even within the fungal pathogens we can find common and unique solutions to maintain metal homeostasis. Thus, we here compare the common and species-specific mechanisms used for different metals among different fungal species-focusing on important human pathogens such as Candida albicans, Aspergillus fumigatus or Cryptococcus neoformans, but also looking at model fungi such as Saccharomyces cerevisiae or A. nidulans as well-studied examples for the underlying principles. These direct comparisons of our current knowledge reveal that we have a good understanding how model fungal pathogens take up iron or zinc, but that much is still to learn about other metals and specific adaptations of individual species-not the least to exploit this knowledge for new antifungal strategies.

Copper transporters are responsible for copper isotopic fractionation in eukaryotic cells

Copper isotopic composition is altered in cancerous compared to healthy tissues. However, the rationale for this difference is yet unknown. As a model of Cu isotopic fractionation, we monitored Cu uptake in Saccharomyces cerevisiae, whose Cu import is similar to human. Wild type cells are enriched in 63Cu relative to 65Cu. Likewise, 63Cu isotope enrichment in cells without high-affinity Cu transporters is of slightly lower magnitude. In cells with compromised Cu reductase activity, however, no isotope fractionation is observed and when Cu is provided solely in reduced form for this strain, copper is enriched in 63Cu like in the case of the wild type. Our results demonstrate that Cu isotope fractionation is generated by membrane importers and that its amplitude is modulated by Cu reduction. Based on ab initio calculations, we propose that the fractionation may be due to Cu binding with sulfur-rich amino acids: methionine and cysteine. In hepatocellular carcinoma (HCC), lower expression of the STEAP3 copper reductase and heavy Cu isotope enrichment have been reported for the tumor mass, relative to the surrounding tissue. Our study suggests that copper isotope fractionation observed in HCC could be due to lower reductase activity in the tumor.

How Mammalian Cells Acquire Copper: An Essential but Potentially Toxic Metal

Cu is an essential micronutrient, and its role in an array of critical physiological processes is receiving increasing attention. Among these are wound healing, angiogenesis, protection against reactive oxygen species, neurotransmitter synthesis, modulation of normal cell and tumor growth, and many others. Free Cu is absent inside cells, and a network of proteins has evolved to deliver this essential, but potentially toxic, metal ion to its intracellular target sites following uptake. Although the total body content is low (∼100 mg), dysfunction of proteins involved in Cu homeostasis results in several well-characterized human disease states. The initial step in cellular Cu handling is its transport across the plasma membrane, a subject of study for only about the last 25 years. This review focuses on the initial step in Cu homeostasis, the properties of the major protein, hCTR1, that mediates Cu uptake, and the status of our understanding of this highly specialized transport system. Although a high-resolution structure of the protein is still lacking, an array of biochemical and biophysical studies have provided a picture of how hCTR1 mediates Cu(I) transport and how Cu is delivered to the proteins in the intracellular milieu. Recent studies provide evidence that the transporter also plays a key protective role in the regulation of cellular Cu via regulatory endocytosis, lowering its surface expression, in response to elevated Cu loads.

Essential and Beneficial Trace Elements in Plants, and Their Transport in Roots: a Review

The essentiality of 14 mineral elements so far have been reported in plant nutrition. Eight of these elements were known as micronutrients due to their lower concentrations in plants (usually ≤100 mg/kg/dw). However, it is still challenging to mention an exact number of plant micronutrients since some elements have not been strictly proposed yet either as essential or beneficial. Micronutrients participate in very diverse metabolic processes, including from the primary and secondary metabolism to the cell defense, and from the signal transduction to the gene regulation, energy metabolism, and hormone perception. Thus, the attempt to understand the molecular mechanism(s) behind their transport has great importance in terms of basic and applied plant sciences. Moreover, their deficiency or toxicity also caused serious disease symptoms in plants, even plant destruction if not treated, and many people around the world suffer from the plant-based dietary deficiencies or metal toxicities. In this sense, shedding some light on this issue, the 13 mineral elements (Fe, B, Cu, Mn, Mo, Si, Zn, Ni, Cl, Se, Na, Al, and Co), required by plants at trace amounts, has been reviewed with the primary focus on the transport proteins (transporters/channels) in plant roots. So, providing the compiled but extensive information about the structural and functional roles of micronutrient transport genes/proteins in plant roots.

Potassium and the K+/H+ Exchanger Kha1p Promote Binding of Copper to ApoFet3p Multi-copper Ferroxidase

Acquisition and distribution of metal ions support a number of biological processes. Here we show that respiratory growth of and iron acquisition by the yeast Saccharomyces cerevisiae relies on potassium (K(+)) compartmentalization to the trans-Golgi network via Kha1p, a K(+)/H(+) exchanger. K(+) in the trans-Golgi network facilitates binding of copper to the Fet3p multi-copper ferroxidase. The effect of K(+) is not dependent on stable binding with Fet3p or alteration of the characteristics of the secretory pathway. The data suggest that K(+) acts as a chemical factor in Fet3p maturation, a role similar to that of cations in folding of nucleic acids. Up-regulation of KHA1 gene in response to iron limitation via iron-specific transcription factors indicates that K(+) compartmentalization is linked to cellular iron homeostasis. Our study reveals a novel functional role of K(+) in the binding of copper to apoFet3p and identifies a K(+)/H(+) exchanger at the secretory pathway as a new molecular factor associated with iron uptake in yeast.

Genome-wide identification and expression profiling of the copper transporter gene family in Populus trichocarpa

Copper transporters (COPT/Ctr) have important roles in the transport of copper (Cu) across the cell membrane in many different species. A comprehensive phylogeny and a molecular structure analysis of the COPT/Ctr family in plants and animals are presented, with an emphasis and bioinformatic analysis of the copper transporter family in Populus trichocarpa (PtCOPT). Structural analyses of PtCOPTs showed that most have 3 transmembrane domains (TMDs), with an exception of PtCOPT4 (2 TMDs). Gene structure, gene chromosomal location, and synteny analyses of PtCOPTs demonstrated that tandem and segmental duplications have likely contributed to the expansion and evolution of the PtCOPTs. Additionally, promoter analyses showed that the function of PtCOPTs is related to Cu and ferrum (Fe) transport. Tissue-specific expression of PtCOPT genes showed that most had relatively high transcript levels in roots and leaves. Quantitative real-time RT-PCR (qRT-PCR) analysis revealed that the expression of PtCOPT genes were induced not only in limited and excessive Cu, Fe, zinc (Zn) and manganese (Mn) stress, but also in lead (Pb), and cadmium (Cd) stress.

New mechanisms that regulate Saccharomyces cerevisiae short peptide transporter achieve balanced intracellular amino acid concentrations

The budding yeast Saccharomyces cerevisiae is able to take up large quantities of amino acids in the form of di- and tripeptides via a short peptide transporter, Ptr2p. It is known that PTR2 can be induced by certain peptides and amino acids, and the mechanisms governing this upregulation are understood at the molecular level. We describe two new opposing mechanisms of regulation that emphasize potential toxicity of amino acids: the first is upregulation of PTR2 in a population of cells, caused by amino acid secretion that accompanies peptide uptake; the second is loss of Ptr2p activity, due to transporter internalization following peptide uptake. Our findings emphasize the importance of proper amino acid balance in the cell and extend understanding of peptide import regulation in yeast.

The copper transporter 1 (CTR1) is required to maintain the stability of copper transporter 2 (CTR2)

Mammalian cells have two influx Cu transporters that form trimers in membranes. CTR1 is the high affinity transporter that resides largely in the plasma membrane, and CTR2 is the low affinity transporter that is primarily associated with vesicular structures inside the cell. The major differences between CTR1 and CTR2 are that CTR1 contains a HIS/MET-rich domain N-terminal of the METS that participate in the first two stacked rings that form the pore, and a longer C-terminal tail that includes a Cu binding HIS-CYS-HIS (HCH) motif right at the end. It has been reported that CTR1 and CTR2 are physically associated with each other in the cell. We used the CRISPR-Cas9 technology to knock out either CTR1 or CTR2 in fully malignant HEK293T and OVCAR8 human ovarian cancer cells to investigate the interaction of CTR1 and CTR2. We report here that the level of CTR2 protein is markedly decreased in CTR1 knockout clones while the CTR2 transcript level remains unchanged. CTR2 was found to be highly ubiquitinated in the CTR1 knock out cells, and inhibition of the proteasome prevented the degradation of CTR2 when CTR1 was not present while inhibition of autophagy had no effect. Re-expression of CTR1 rescued CTR2 from degradation in the CTR1 knockout cells. We conclude that CTR1 is essential to maintain the stability of CTR2 and that in the absence of CTR1 CTR2 is degraded by the proteasome. This reinforces the concept that the functions of CTR1 and CTR2 are inter-dependent within the Cu homeostasis system.

Molecular mechanisms underlying copper homeostasis in Mammalian cells

Copper (Cu) is an essential metal for living organisms that utilize oxygen for respiration and is required as a cofactor of redox-regulating enzymes, such as superoxide dismutase, ceruloplasmin, lysyl oxidase, tyrosinase, and dopamine β-hydroxylase. However, the redox-active property of this metal may have toxic effects on cells due to the generation of harmful reactive oxygen species. Given these circumstances, it is said that cells have a dependable system for Cu homeostasis that efficiently distributes this essential metal to cuproenzymes, thereby preventing damage to proteins, nucleic acids, sugars, and lipids. In particular, influx, efflux, and intracellular distribution with maintenance of the oxidation state of Cu are strictly regulated. Several groups of Cu-regulating factors have been identified in mammalian cells, i.e., Cu transporters, Cu chaperones, Cu-binding proteins/peptides, and others. In this review, the features of the Cu-regulating factors are concisely examined in terms of molecular mechanisms underlying Cu homeostasis in cells.

Copper in Eukaryotes

Copper is essential for normal growth and development of eukaryotic organisms. Numerous physiological processes rely on sufficient availability of copper: from indispensable reactions such as mitochondrial respiration to more highly specialized processes such as pigment development in a skin. Copper misbalance has been linked to a variety of metabolic and neurodegenerative disorders in humans. Complex cellular machinery has evolved to mediate copper uptake, compartmentalization and incorporation into target proteins. Extensive studies revealed a predominant utilization of methionines and histidines by copper handling molecules for copper capture at the extracellular surface and delivery to cuproenzymes in the lumen of cellular compartments, respectively. Cu(I) is a predominant form within the cell, and copper binding and distribution inside the cell at the cytosolic sites relies heavily on cysteines. The selectivity and directionality of copper transfer reactions is determined by thermodynamic and kinetic factors as well as spatial distribution of copper donors and acceptors. In this chapter, we review current structural and mechanistic data on copper transport and distribution in yeast and mammalian cells and highlight important issues and questions for future studies.

Molecular modulation of the copper and cisplatin transport function of CTR1 and its interaction with IRS-4

The copper influx transporter CTR1 is also a major influx transporter for cisplatin (cDDP) in tumor cells. It influences the cytotoxicity of cDDP both in vivo and in vitro. Whereas Cu triggers internalization of CTR1 from the plasma membrane, cDDP does not. To investigate the mechanisms of these effects, myc-tagged forms of wild type hCTR1 and variants in which Y103 was converted to alanine, C189 was converted to serine, or the K178/K179 dilysine motif was converted to alanines were re-expressed in mouse embryo cells in which both alleles of CTR1 had been knocked out and also in HEK293T cells. The Y103A mutation and to a lesser extent the C189S mutation reduced internalization of CTR1 induced by Cu while the K178A/K179A had little effect. Both Y103 and C189 were required for Cu and cDDP transport whereas the K178/K179 motif was not. While Y103 lies in an YXXM motif that, when phosphorylated, is a potential docking site for phosphatidylinositol 3-kinase and other proteins involved in endocytosis, Western blot analysis of immunoprecipitated myc-CTR1, and proteomic analysis of peptides derived from CTR1, failed to identify any basal or Cu-induced phosphorylation. However, proteomic analysis did identify an interaction of CTR1 with IRS-4 and this was confirmed by co-immunoprecipitation from HEK cells expressing either FLAG-CTR1 or myc-CTR1. The interaction was greater in the Y103A-expressing cells. We conclude that Y103 is required for the internalization of hCTR1 in response to Cu, that this occurs by a mechanism other than phosphorylation and that mutation of Y103 modulates the interaction with IRS-4.

Brachypodium distachyon as a model system for studies of copper transport in cereal crops

Copper (Cu) is an essential micronutrient that performs a remarkable array of functions in plants including photosynthesis, cell wall remodeling, flowering, and seed set. Of the world's major cereal crops, wheat, barley, and oat are the most sensitive to Cu deficiency. Cu deficient soils include alkaline soils, which occupy approximately 30% of the world's arable lands, and organic soils that occupy an estimated 19% of arable land in Europe. We used Brachypodium distachyon (brachypodium) as a proxy for wheat and other grain cereals to initiate analyses of the molecular mechanisms underlying their increased susceptibility to Cu deficiency. In this report, we focus on members of the CTR/COPT family of Cu transporters because their homologs in A. thaliana are transcriptionally upregulated in Cu-limited conditions and are involved either in Cu uptake from soils into epidermal cells in the root, or long-distance transport and distribution of Cu in photosynthetic tissues. We found that of five COPT proteins in brachypodium, BdCOPT3, and BdCOPT4 localize to the plasma membrane and are transcriptionally upregulated in roots and leaves by Cu deficiency. We also found that BdCOPT3, BdCOPT4, and BdCOPT5 confer low affinity Cu transport, in contrast to their counterparts in A. thaliana that confer high affinity Cu transport. These data suggest that increased sensitivity to Cu deficiency in some grass species may arise from lower efficiency and, possibly, other properties of components of Cu uptake and tissue partitioning systems and reinforce the importance of using brachypodium as a model for the comprehensive analyses of Cu homeostasis in cereal crops.

The families of zinc (SLC30 and SLC39) and copper (SLC31) transporters

The solute carriers families 30 (SLC30; ZnT), 39 (SLC39; ZIP), and 31 (SLC31; CTR) are involved in the essential maintenance of cellular zinc (Zn²⁺) and copper (Cu²⁺) homeostasis, respectively. ZnTs mediate Zn²⁺ extrusion from cells (SLC30A1) or transport Zn²⁺ into organelles and secretory vesicles/granules (SLC30A2-SLC30A8). SLC39 family members are predominantly localized to the cell membrane where they perform Zn²⁺ uptake and increase the availability of cytosolic Zn²⁺. SLC39A1 is ubiquitously expressed, whereas other ZIP transporters (e.g., SLC39A2 and SLC39A3) show a more tissue-restricted expression consistent with organ-specific functions of these proteins. The members A1 (CTR1) and A2 (CTR2) of the SLC31 family of solute carriers belong to a network of proteins that acts to regulate the intracellular Cu²⁺ concentration within a certain range. SLC31A1 is predominantly localized to the plasma membrane, whereas SLC31A2 is mainly found in intracellular membranes of the late endosome and lysosome. The specific function of SLC31A2 is not known. SLC31A1 is ubiquitously expressed and has been characterized as a high-affinity importer of reduced copper (Cu⁺). Cu²⁺ transport function of CTR proteins is associated with oligomerization; SLC31A1 trimerizes and thereby forms a channel-like structure enabling Cu²⁺ translocation across the cell membrane. The molecular characteristics and structural details (e.g., membrane topology, conserved Zn²⁺, and Cu²⁺ binding sites) and mechanisms of translational and posttranslational regulation of expression and/or activity have been described for SLC30 and SLC39 family members, and for SLC31A1. For SLC31A1, data on tissue-specific functions (e.g., in the intestine, heart, and liver) are also available. A link between SLC31A1, immune function, and disorders such as Alzheimer's disease or cancer makes the protein a candidate therapeutic target. In secretory tissues (e.g., the mammary gland and pancreas), Zn²⁺ transporters of SLC families 30 and 39 are involved in specific functions such as insulin synthesis and secretion, metallation of digestive proenzymes, and transfer of nutrients into milk. Defective or dysregulated Zn²⁺ metabolism in these organs is associated with disorders such as diabetes and cancer, and impaired Zn²⁺ secretion into milk.

SLC31 (CTR) family of copper transporters in health and disease

Copper is a vital mineral for many organisms, yet it is highly toxic as demonstrated by serious health concerns associated with its deficiency or excess accumulation. The SLC31 (CTR) family of copper transporters is a major gateway of copper acquisition in eukaryotes, ranging from yeast to humans. Characterization of the function, modes of action, and regulation of CTR and other molecular factors that functionally cooperate with CTR for copper transport, compartmentalization, incorporation into cuproproteins, and detoxification has revealed that organisms have evolved fascinating mechanisms for tight control of copper metabolism. This research progress further indicates the significance of copper in health and disease and opens avenues for therapeutic control of copper bioavailability and its metabolic pathways.

A basic set of homeostatic controller motifs

Adaptation and homeostasis are essential properties of all living systems. However, our knowledge about the reaction kinetic mechanisms leading to robust homeostatic behavior in the presence of environmental perturbations is still poor. Here, we describe, and provide physiological examples of, a set of two-component controller motifs that show robust homeostasis. This basic set of controller motifs, which can be considered as complete, divides into two operational work modes, termed as inflow and outflow control. We show how controller combinations within a cell can integrate uptake and metabolization of a homeostatic controlled species and how pathways can be activated and lead to the formation of alternative products, as observed, for example, in the change of fermentation products by microorganisms when the supply of the carbon source is altered. The antagonistic character of hormonal control systems can be understood by a combination of inflow and outflow controllers.

Rate and regulation of copper transport by human copper transporter 1 (hCTR1)

Human copper transporter 1 (hCTR1) is a homotrimer of a 190-amino acid monomer having three transmembrane domains believed to form a pore for copper permeation through the plasma membrane. The hCTR1-mediated copper transport mechanism is not well understood, nor has any measurement been made of the rate at which copper ions are transported by hCTR1. In this study, we estimated the rate of copper transport by the hCTR1 trimer in cultured cells using (64)Cu uptake assays and quantification of plasma membrane hCTR1. For endogenous hCTR1, we estimated a turnover number of about 10 ions/trimer/s. When overexpressed in HEK293 cells, a second transmembrane domain mutant of hCTR1 (H139R) had a 3-fold higher Km value and a 4-fold higher turnover number than WT. Truncations of the intracellular C-terminal tail and an AAA substitution of the putative metal-binding HCH C-terminal tripeptide (thought to be required for transport) also exhibited elevated transport rates and Km values when compared with WT hCTR1. Unlike WT hCTR1, H139R and the C-terminal mutants did not undergo regulatory endocytosis in elevated copper. hCTR1 mutants combining methionine substitutions that block transport (M150L,M154L) on the extracellular side of the pore and the high transport H139R or AAA intracellular side mutations exhibited the blocked transport of M150L,M154L, confirming that Cu(+) first interacts with the methionines during permeation. Our results show that hCTR1 elements on the intracellular side of the hCTR1 pore, including the carboxyl tail, are not essential for permeation, but serve to regulate the rate of copper entry.

Overexpression of ctr1Δ300, a high-affinity copper transporter with deletion of the cytosolic C-terminus in Saccharomyces cerevisiae under excess copper, leads to disruption of transition metal homeostasis and transcriptional remodelling of cellular processes

In an approach to generating Saccharomyces cerevisiae strains with increased intracellular copper amounts for technical applications, we overexpressed the copper transporter CTR1 and a variant of CTR1 with a truncation in the C-terminus after the 300th amino acid (ctr1Δ300). We determined the copper sensitivity of the generated strains and used inductively coupled plasma spectrometry analysis (ICP-OES and ICP-MS) to investigate the effects of overexpression of both constructs under excess copper on the cellular content of different elements in S. cerevisiae. In addition, we performed DNA microarray analysis to obtain the gene expression profile under the changed element contents. Overexpression of CTR1 increased the copper content in the cells to 160% and 78 genes were differentially regulated. Overexpression of the truncated ctr1Δ300 resulted in an increased copper, iron and zinc content of > 200% and 980 genes showed differential expression. We found that transition metal ion homeostasis was disrupted in ctr1Δ300-overexpressing strains under excess copper and that this was combined with a transcriptional remodelling of cellular processes.

Calcium- and potassium-permeable plasma membrane transporters are activated by copper in Arabidopsis root tips: linking copper transport with cytosolic hydroxyl radical production

Transition metals such as copper can interact with ascorbate or hydrogen peroxide to form highly reactive hydroxyl radicals (OH(•) ), with numerous implications to membrane transport activity and cell metabolism. So far, such interaction was described for extracellular (apoplastic) space but not cytosol. Here, a range of advanced electrophysiological and imaging techniques were applied to Arabidopsis thaliana plants differing in their copper-transport activity: Col-0, high-affinity copper transporter COPT1-overexpressing (C1(OE) ) seedlings, and T-DNA COPT1 insertion mutant (copt1). Low Cu concentrations (10 µm) stimulated a dose-dependent Gd(3+) and verapamil sensitive net Ca(2+) influx in the root apex but not in mature zone. C1(OE) also showed a fivefold higher Cu-induced K(+) efflux at the root tip level compared with Col-0, and a reduction in basal peroxide accumulation at the root tip after copper exposure. Copper caused membrane disruptions of the root apex in C1(OE) seedlings but not in copt1 plants; this damage was prevented by pretreatment with Gd(3+) . Our results suggest that copper transport into cytosol in root apex results in hydroxyl radical generation at the cytosolic side, with a consequent regulation of plasma membrane OH(•) -sensitive Ca(2+) and K(+) transport systems.

A Plasmodium falciparum copper-binding membrane protein with copper transport motifs

Background

Copper is an essential catalytic co-factor for metabolically important cellular enzymes, such as cytochrome-c oxidase. Eukaryotic cells acquire copper through a copper transport protein and distribute intracellular copper using molecular chaperones. The copper chelator, neocuproine, inhibits Plasmodium falciparum ring-to-trophozoite transition in vitro, indicating a copper requirement for malaria parasite development. How the malaria parasite acquires or secretes copper still remains to be fully elucidated.

Methods

PlasmoDB was searched for sequences corresponding to candidate P. falciparum copper-requiring proteins. The amino terminal domain of a putative P. falciparum copper transport protein was cloned and expressed as a maltose binding fusion protein. The copper binding ability of this protein was examined. Copper transport protein-specific anti-peptide antibodies were generated in chickens and used to establish native protein localization in P. falciparum parasites by immunofluorescence microscopy.

Results

Six P. falciparum copper-requiring protein orthologs and a candidate P. falciparum copper transport protein (PF14_0369), containing characteristic copper transport protein features, were identified in PlasmoDB. The recombinant amino terminal domain of the transport protein bound reduced copper in vitro and within Escherichia coli cells during recombinant expression. Immunolocalization studies tracked the copper binding protein translocating from the erythrocyte plasma membrane in early ring stage to a parasite membrane as the parasites developed to schizonts. The protein appears to be a PEXEL-negative membrane protein.

Conclusion

Plasmodium falciparum parasites express a native protein with copper transporter characteristics that binds copper in vitro. Localization of the protein to the erythrocyte and parasite plasma membranes could provide a mechanism for the delivery of novel anti-malarial compounds.

Copper transport and compartmentation in grape cells

Copper-based fungicides have been widely used against several grapevine (Vitis vinifera L.) diseases since the late 1800s when the Bordeaux mixture was developed, but their intensive use has raised phytotoxicity concerns. In this study, physiological, biochemical and molecular approaches were combined to investigate the impacts of copper in grape cells and how it is transported and compartmented intracellularly. Copper reduced the growth and viability of grape cells (CSB, Cabernet Sauvignon Berry) in a dose-dependent manner above 100 µM and was accumulated in specific metal ion sinks. The copper-sensitive probe Phen Green SK was used to characterize copper transport across the plasma membrane of CSB cells. The transport system (K(m) = 583 µM; V(max) = 177 × 10(-6) %ΔF min(-1) protoplast(-1)) was regulated by copper availability in the culture medium, stimulated by Ca(2+) and inhibited by Zn(2+). The pH-sensitive fluorescent probe ACMA (9-amino-6-chloro-2-methoxyacridine) was used to evaluate the involvement of proton-dependent copper transport across the tonoplast. Cu(2+) compartmentation in the vacuole was dependent on the transmembrane pH gradient generated by both V-H(+)-ATPase and V-H(+)-pyrophosphatase (PPase). High copper levels in the growth medium did not affect the activity of V-H(+)-PPase but decreased the magnitude of the H(+) gradient generated by V-H(+)-ATPase. Expression studies of VvCTr genes showed that VvCTr1 and VvCTr8 were distinctly affected by CuSO(4) availability in grape cell cultures and that both genes were highly expressed in the green stage of grape berries.

Evolution of copper transporting ATPases in eukaryotic organisms

Copper is an essential nutrient for most life forms, however in excess it can be harmful. The ATP-driven copper pumps (Copper-ATPases) play critical role in living organisms by maintaining appropriate copper levels in cells and tissues. These evolutionary conserved polytopic membrane proteins are present in all phyla from simplest life forms (bacteria) to highly evolved eukaryotes (Homo sapiens). The presumed early function in metal detoxification remains the main function of Copper-ATPases in prokaryotic kingdom. In eukaryotes, in addition to removing excess copper from the cell, Copper-ATPases have another equally important function - to supply copper to copper dependent enzymes within the secretory pathway. This review focuses on the origin and diversification of Copper ATPases in eukaryotic organisms. From a single Copper ATPase in protozoans, a divergence into two functionally distinct ATPases is observed with the evolutionary appearance of chordates. Among the key functional domains of Copper-ATPases, the metal-binding N-terminal domain could be responsible for functional diversification of the copper ATPases during the course of evolution.

COPT6 is a plasma membrane transporter that functions in copper homeostasis in Arabidopsis and is a novel target of SQUAMOSA promoter-binding protein-like 7

Among the mechanisms controlling copper homeostasis in plants is the regulation of its uptake and tissue partitioning. Here we characterized a newly identified member of the conserved CTR/COPT family of copper transporters in Arabidopsis thaliana, COPT6. We showed that COPT6 resides at the plasma membrane and mediates copper accumulation when expressed in the Saccharomyces cerevisiae copper uptake mutant. Although the primary sequence of COPT6 contains the family conserved domains, including methionine-rich motifs in the extracellular N-terminal domain and a second transmembrane helix (TM2), it is different from the founding family member, S. cerevisiae Ctr1p. This conclusion was based on the finding that although the positionally conserved Met(106) residue in the TM2 of COPT6 is functionally essential, the conserved Met(27) in the N-terminal domain is not. Structure-function studies revealed that the N-terminal domain is dispensable for COPT6 function in copper-replete conditions but is important under copper-limiting conditions. In addition, COPT6 interacts with itself and with its homolog, COPT1, unlike Ctr1p, which interacts only with itself. Analyses of the expression pattern showed that although COPT6 is expressed in different cell types of different plant organs, the bulk of its expression is located in the vasculature. We also show that COPT6 expression is regulated by copper availability that, in part, is controlled by a master regulator of copper homeostasis, SPL7. Finally, studies using the A. thaliana copt6-1 mutant and plants overexpressing COPT6 revealed its essential role during copper limitation and excess.