Highly selective tungstate transporter protein TupA from Desulfovibrio alaskensis G20

Overexpression of a Designed Mutant Oxyanion Binding Protein ModA/WtpA in Acidithiobacillus ferrooxidans for the Low pH Recovery of Molybdenum and Rhenium

Molybdenum and rhenium are critically important metals for a number of emerging technologies. We identified and characterized a molybdenum/tungsten transport protein (ModA/WtpA) of Acidithiobacillus ferrooxidans and demonstrated the binding of tungstate, molybdate, and chromate. We used computational design to expand the binding capabilities of the protein to include perrhenate. A disulfide bond was engineered into the binding pocket of ModA/WtpA to introduce a more favorable geometric coordination and surface charge distribution for oxyanion binding. The mutant protein experimentally demonstrated a 2-fold higher binding affinity for molybdate and 6-fold higher affinity for perrhenate. The overexpression of the wild-type and mutant ModA/WtpA proteins in A. ferrooxidans cells enhanced the innate tungstate, molybdate, and chromate binding capacities of the cells to up to 2-fold higher. In addition, the engineered cells expressing the mutant protein exhibited enhanced perrhenate binding, showing 5-fold and 2-fold higher binding capacities compared to the wild-type and ModA/WtpA-overexpressing cells, respectively. Furthermore, the engineered cell lines enhanced biocorrosion of stainless steel as well as the recovered valuable metals from an acidic wastewater generated from molybdenite processing. The improved binding efficiency for the oxyanion metals, along with the high selectivity over nontargeted metals under mixed metal environments, highlights the potential value of the engineered strains for practical microbial metal reclamation under low pH conditions.

Marinobacter atlanticus electrode biofilms differentially regulate gene expression depending on electrode potential and lifestyle

Marinobacter spp. are opportunitrophs with a broad metabolic range including interactions with metals and electrodes. Marinobacter atlanticus strain CP1 was previously isolated from a cathode biofilm microbial community enriched from a sediment microbial fuel cell. Like other Marinobacter spp., M. atlanticus generates small amounts of electrical current when grown as a biofilm on an electrode, which is enhanced by the addition of redox mediators. However, the molecular mechanism resulting in extracellular electron transfer is unknown. Here, RNA-sequencing was used to determine changes in gene expression in electrode-attached and planktonic cells of M. atlanticus when grown at electrode potentials that enable current production (310 and 510 mV vs. SHE) compared to a potential that enables electron uptake (160 mV). Cells grown at current-producing potentials had increased expression of genes for molybdate transport, regardless of planktonic or attached lifestyle. Electrode-attached cells at current-producing potentials showed increased expression of the major export protein for the type VI secretion system. Growth at 160 mV resulted in an increase in expression of genes related to stress response and DNA repair including both RecBCD and the LexA/RecA regulatory network, as well as genes for copper homeostasis. Changes in expression of proteins with PEP C-terminal extracellular export motifs suggests that M. atlanticus is remodeling the biofilm matrix in response to electrode potential. These results improve our understanding of the physiological adaptations required for M. atlanticus growth on electrodes, and suggest a role for metal acquisition, either as a requirement for metal cofactors of redox proteins or as a possible electron shuttling mechanism.

Tungstoenzymes: Occurrence, Catalytic Diversity and Cofactor Synthesis

Tungsten is the heaviest element used in biological systems. It occurs in the active sites of several bacterial or archaeal enzymes and is ligated to an organic cofactor (metallopterin or metal binding pterin; MPT) which is referred to as tungsten cofactor (Wco). Wco-containing enzymes are found in the dimethyl sulfoxide reductase (DMSOR) and the aldehyde:ferredoxin oxidoreductase (AOR) families of MPT-containing enzymes. Some depend on Wco, such as aldehyde oxidoreductases (AORs), class II benzoyl-CoA reductases (BCRs) and acetylene hydratases (AHs), whereas others may incorporate either Wco or molybdenum cofactor (Moco), such as formate dehydrogenases, formylmethanofuran dehydrogenases or nitrate reductases. The obligately tungsten-dependent enzymes catalyze rather unusual reactions such as ones with extremely low-potential electron transfers (AOR, BCR) or an unusual hydration reaction (AH). In recent years, insights into the structure and function of many tungstoenzymes have been obtained. Though specific and unspecific ABC transporter uptake systems have been described for tungstate and molybdate, only little is known about further discriminative steps in Moco and Wco biosynthesis. In bacteria producing Moco- and Wco-containing enzymes simultaneously, paralogous isoforms of the metal insertase MoeA may be specifically involved in the molybdenum- and tungsten-insertion into MPT, and in targeting Moco or Wco to their respective apo-enzymes. Wco-containing enzymes are of emerging biotechnological interest for a number of applications such as the biocatalytic reduction of CO2, carboxylic acids and aromatic compounds, or the conversion of acetylene to acetaldehyde.

Efficient bioaccumulation of tungsten by Escherichia coli cells expressing the Sulfitobacter dubius TupBCA system

Tungsten (W) is a valuable element with considerable industrial and economic importance that belongs to the European Union list of critical metals with a high supply risk. Therefore, the development of effective and new methods for W recovery is essential to ensure a sustainable supply. In the present study, the Sulfitobacter dubius W transport system TupABC was explored in order to demonstrate both its functionality in Escherichia coli cells and to construct a bioaccumulator (EcotupW). The complete gene cluster tupBCA or partial gene cluster tupBC were cloned in an expression vector and transformed into E. coli. Metal accumulation was evaluated when each construct strain was grown with three separate metal oxyanions (tungstate, molybdate or chromate). The specificity of the bioaccumulator was determined by competition assays using cells grown with mixed solutions of metal oxyanions (W/Mo and W/Cr). The results showed the relevance of the TupA protein in the TupABC transporter system to W-uptake and also allowed Mo and Cr accumulations, although with amounts 1.7 and 2.9-fold lower than W, respectively. To identify the importance of the valine residue in the accumulation efficiency of the VTTS motif, site-directed mutagenesis of tupA was performed. A mutant with a threonine residue, instead of the respective valine, confirmed that W was internalized by nearly double the amount compared to the native form. The findings indicated that cells carrying the native S. dubius TupABC system were great W-bioaccumulators and could be promising tools for W recovery.

Shedding Light on the Interaction of Human Anti-Apoptotic Bcl-2 Protein with Ligands through Biophysical and in Silico Studies

Bcl-2 protein is involved in cell apoptosis and is considered an interesting target for anti-cancer therapy. The present study aims to understand the stability and conformational changes of Bcl-2 upon interaction with the inhibitor venetoclax, and to explore other drug-target regions. We combined biophysical and in silico approaches to understand the mechanism of ligand binding to Bcl-2. Thermal shift assay (TSA) and urea electrophoresis showed a significant increase in protein stability upon venetoclax incubation, which is corroborated by molecular docking and molecular dynamics simulations. An 18 °C shift in Bcl-2 melting temperature was observed in the TSA, corresponding to a binding affinity multiple times higher than that of any other reported Bcl-2 inhibitor. This protein-ligand interaction does not implicate alternations in protein conformation, as suggested by SAXS. Additionally, bioinformatics approaches were used to identify deleterious non-synonymous single nucleotide polymorphisms (nsSNPs) of Bcl-2 and their impact on venetoclax binding, suggesting that venetoclax interaction is generally favored against these deleterious nsSNPs. Apart from the BH3 binding groove of Bcl-2, the flexible loop domain (FLD) also plays an important role in regulating the apoptotic process. High-throughput virtual screening (HTVS) identified 5 putative FLD inhibitors from the Zinc database, showing nanomolar affinity toward the FLD of Bcl-2.

Designating ligand specificities to metal uptake ABC transporters in Thermus thermophilus HB8

Acquisition of different metal ions by metal uptake ABC transporters of Thermus thermophilus HB8 for accomplishing its various cellular functions.