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The C-Terminus of Human Copper Importer Ctr1 Acts as a Binding Site and Transfers Copper to Atox1.

ABSTRACT: Uptake of copper (Cu) ions into human cells is mediated by the plasma membrane protein Ctr1 and is followed by Cu transfer to cytoplasmic Cu chaperones for delivery to Cu-dependent enzymes. The C-terminal cytoplasmic tail of Ctr1 is a 13-residue peptide harboring an HCH motif that is thought to interact with Cu. We here employ biophysical experiments under anaerobic conditions in peptide models of the Ctr1 C-terminus to deduce Cu-binding residues, Cu affinity, and the ability to release Cu to the cytoplasmic Cu chaperone Atox1. Based on NMR assignments and bicinchoninic acid competition experiments, we demonstrate that Cu interacts in a 1:1 stoichiometry with the HCH motif with an affinity, KD, of ∼10(-14) M. Removing either the Cys residue or the two His residues lowers the Cu-peptide affinity, but site specificity is retained. The C-terminal peptide and Atox1 do not interact in solution in the absence of Cu. However, as directly demonstrated at the residue level via NMR spectroscopy, Atox1 readily acquires Cu from the Cu-loaded peptide. We propose that Cu binding to the Ctr1 C-terminal tail regulates Cu transport into the cytoplasm such that the metal ion is only released to high-affinity Cu chaperones.

SUBMITTER: Kahra D

PROVIDER: S-EPMC4805863 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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The C-Terminus of Human Copper Importer Ctr1 Acts as a Binding Site and Transfers Copper to Atox1.

Kahra Dana D Kovermann Michael M Wittung-Stafshede Pernilla P

Biophysical journal 20160101 1

Uptake of copper (Cu) ions into human cells is mediated by the plasma membrane protein Ctr1 and is followed by Cu transfer to cytoplasmic Cu chaperones for delivery to Cu-dependent enzymes. The C-terminal cytoplasmic tail of Ctr1 is a 13-residue peptide harboring an HCH motif that is thought to interact with Cu. We here employ biophysical experiments under anaerobic conditions in peptide models of the Ctr1 C-terminus to deduce Cu-binding residues, Cu affinity, and the ability to release Cu to th ...[more]

PMID: 26745413

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Project description:UnlabelledUptake and trafficking of metals and their delivery to their respective metalloproteins are important processes. Cells need precise control of each step to avoid exposure to excessive metal concentrations and their harmful consequences. Copper (Cu) is a required micronutrient used as a cofactor in proteins. However, in large amounts, it can induce oxidative damage; hence, Cu homeostasis is indispensable for cell survival. Biogenesis of respiratory heme-Cu oxygen (HCO) reductases includes insertion of Cu into their catalytic subunits to form heme-Cu binuclear centers. Previously, we had shown that CcoA is a major facilitator superfamily (MFS)-type bacterial Cu importer required for biogenesis of cbb3-type cytochrome c oxidase (cbb3-Cox). Here, using Rhodobacter capsulatus, we focused on the import and delivery of Cu to cbb3-Cox. By comparing the CcoA amino acid sequence with its homologues from other bacterial species, we located several well-conserved Met, His, and Tyr residues that might be important for Cu transport. We determined the topology of the transmembrane helices that carry these residues to establish that they are membrane embedded, and substituted for them amino acids that do not ligand metal atoms. Characterization of these mutants for their uptake of radioactive (64)Cu and cbb3-Cox activities demonstrated that Met233 and His261 of CcoA are essential and Met237 and Met265 are important, whereas Tyr230 has no role for Cu uptake or cbb3-Cox biogenesis. These findings show for the first time that CcoA-mediated Cu import relies on conserved Met and His residues that could act as metal ligands at the membrane-embedded Cu binding domain of this transporter.ImportanceCu is a micronutrient that is both essential and toxic; hence, its cellular homeostasis is crucial. Respiratory cbb3-type cytochrome c oxidases (cbb3-Cox) are Cu-containing energy-transducing enzymes that are important for many microaerophilic processes, including photosynthesis, respiration, and bacterial pathogenesis. How Cu is incorporated into cbb3-Cox enzymes is not well known. So far, CcoA is the only known major facilitator superfamily (MFS)-type transporter required for Cu import into the bacterial cytoplasm and for cbb3-Cox biogenesis. This study shows that the membrane-embedded, universally conserved Met and His residues of CcoA are essential for its Cu import function and also for its role in cbb3-Cox biogenesis, shedding light on the mechanism of function of this bacterial prototypical Cu importer.

Project description:BackgroundNon-small cell lung cancer (NSCLC) is associated with intracellular copper accumulation. Antioxidant 1 (ATOX1) is a copper chaperone. This study aimed to analyze the anti-cancer effects of curcumin on the ATOX1-mediated copper pathway in NSCLC.MethodsA binding activity between curcumin and ATOX1 was measured using molecular docking. NSCLC cells, A549 and H1299, were treated with different doses of curcumin (10, 20, 40 µM) or DC-AC50 (5, 10, 20 µM) for 24 h. The cell viability and levels of ATOX1, ATP7A and COX17 proteins were observed in cells. Overexpressing ATOX1 in cells was established by pcDNA3.1-ATOX1 transfection for 24 h. The ATOX1 overexpressing cells were treated with 40 µM curcumin or 20 µM DC-AC50 for 24 h to analyze the mechanism of curcumin in NSCLC treatment. Cell viability was measured by CCK-8, and levels of proteins were measured by western blotting. The copper level in cells was labeled by copper sensor-1. Moreover, nude mice models were induced by injection of A549 cells and treated with 20 mg/kg/d DC-AC50 or 40 mg/kg/d curcumin. Tumor growth was observed by measuring tumor volume and tumor weight. The levels of ATOX1, ATP7A and COX17 in tumors were measured by immunohistochemistry and western blotting.ResultsCurcumin bound to ATOX1 (score = -6.1 kcal/mol) and decreased the levels of ATOX1, ATP7A and COX17 proteins in NSCLC cells. The curcumin or DC-AC50 treatment suppressed cell viability by inhibiting the ATOX1-mediated copper signaling in NSCLC cells. The ATOX1 overexpression in cells significantly weakened the effects of curcumin on suppressing copper accumulation and the ATOX1-mediated copper pathway (p < 0.05). In mice models, curcumin or DC-AC50 treatment also suppressed tumor growth by suppressing the ATOX1-mediated copper pathway in tumors.ConclusionThis study demonstrated that curcumin bound ATOX1 to suppress copper accumulation in NSCLC cells, providing a new mechanism of curcumin for NSCLC treatment.

Dataset Information

The C-Terminus of Human Copper Importer Ctr1 Acts as a Binding Site and Transfers Copper to Atox1.

Publications

The C-Terminus of Human Copper Importer Ctr1 Acts as a Binding Site and Transfers Copper to Atox1.

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