Site-directed mutagenesis reveals a conservation of the copper-binding site and the crucial role of His24 in CopH from Cupriavidus metallidurans CH34

Responses to copper stress in the metal-resistant bacterium Cupriavidus gilardii CR3: a whole-transcriptome analysis

Microbial metal-resistance mechanisms are the basis for the application of microorganisms in metal bioremediation. Despite the available studies of bacterial molecular mechanisms to resistance metals ions (particularly copper), the understanding of bacterial metal resistance is very limited from the transcriptome perspective. Here, responses of the transcriptome (RNA-Seq) was investigated in Cupriavidus gilardii CR3 exposed to 0.5 mM copper, because strain CR3 had a bioremoval capacity of 38.5% for 0.5 mM copper. More than 24 million clean reads were obtained from six libraries and were aligned against the C. gilardii CR3 genome. A total of 310 genes in strain CR3 were significantly differentially expressed under copper stress. Apart from the routine copper resistance operons cus and cop known in previous studies, Gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses of differentially expressed genes indicated that the adenosine triphosphate-binding cassette transporter, amino acid metabolism, and negative chemotaxis collectively contribute to the copper-resistant process. More interestingly, we found that the genes associated with the type III secretion system were induced under copper stress. No such results were reordered in bacteria to date. Overall, this comprehensive network of copper responses is useful for further studies of the molecular mechanisms underlying responses to copper stress in bacteria.

Multiple Transcriptional Mechanisms Collectively Mediate Copper Resistance in Cupriavidus gilardii CR3

Bacteria resist copper (Cu) stress by implementing several metabolic mechanisms. However, these mechanisms are not fully understood. We investigated the mechanism of Cu resistance in Cupriavidus gilardii CR3, a Cu-resistant bacterium with a fully sequenced, annotated genome. The growth of CR3 was inhibited by higher Cu concentrations (≥1.0 mM) but not by lower ones (≤0.5 mM). CR3 accumulated Cu intracellularly (ratios of intercellular to extracellular Cu were 11.6, 4.24, and 3.9 in 0.1, 0.5, and 1.5 mM Cu treatments, respectively). A comparative transcriptome analysis of CR3 respectively revealed 310 and 413 differentially expressed genes under 0.5 and 1.5 mM Cu stress, most of which were up-regulated under Cu treatment. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes functional enrichment analyses uncovered several genotype-specific biological processes related to Cu stress. Besides revealing known Cu resistance-related genes, our global transcriptomics approach indicated that sulfur metabolism, iron-sulfur cluster, and cell secretion systems are involved in mediating Cu resistance in strain CR3. These results suggest that bacteria collectively use multiple systems to cope with Cu stress. Our findings concerning the global transcriptome response to Cu stress in CR3 provide new information for understanding the intricate regulatory network of Cu homeostasis in prokaryotes.

Cu binding by the Escherichia coli metal-efflux accessory protein RcnB

RcnB is a novel Cu-binding protein involved in Ni and Co detoxification.

Pulsed electron spin resonance resolves the coordination site of Cu²(+) ions in α1-glycine receptor

Herein, we identify the coordination environment of Cu²(+) in the human α1-glycine receptor (GlyR). GlyRs are members of the pentameric ligand-gated ion channel superfamily (pLGIC) that mediate fast signaling at synapses. Metal ions like Zn²(+) and Cu²(+) significantly modulate the activity of pLGICs, and metal ion coordination is essential for proper physiological postsynaptic inhibition by GlyR in vivo. Zn²(+) can either potentiate or inhibit GlyR activity depending on its concentration, while Cu²(+) is inhibitory. To better understand the molecular basis of the inhibitory effect we have used electron spin resonance to directly examine Cu²(+) coordination and stoichiometry. We show that Cu²(+) has one binding site per α1 subunit, and that five Cu²(+) can be coordinated per GlyR. Cu²(+) binds to E192 and H215 in each subunit of GlyR with a 40 μM apparent dissociation constant, consistent with earlier functional measurements. However, the coordination site does not include several residues of the agonist/antagonist binding site that were previously suggested to have roles in Cu²(+) coordination by functional measurements. Intriguingly, the E192/H215 site has been proposed as the potentiating Zn²(+) site. The opposing modulatory actions of these cations at a shared binding site highlight the sensitive allosteric nature of GlyR.