Existence of a tungsten-binding protein in Acidithiobacillus ferrooxidans AP19-3

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.

The linkage between ribosomal crystallography, metal ions, heteropolytungstates and functional flexibility

Crystallography of ribosomes, the universal cell nucleoprotein assemblies facilitating the translation of the genetic-code into proteins, met with severe problems owing to their large size, complex structure, inherent flexibility and high conformational variability. For the case of the small ribosomal subunit, which caused extreme difficulties, post crystallization treatment by minute amounts of a heteropolytungstate cluster allowed structure determination at atomic resolution. This cluster played a dual role in ribosomal crystallography: providing anomalous phasing power and dramatically increased the resolution, by stabilization of a selected functional conformation. Thus, four out of the fourteen clusters that bind to each of the crystallized small subunits are attached to a specific ribosomal protein in a fashion that may control a significant component of the subunit internal flexibility, by "gluing" symmetrical related subunits. Here we highlight basic issues in the relationship between metal ions and macromolecules and present common traits controlling in the interactions between polymetalates and various macromolecules, which may be extended towards the exploitation of polymetalates for therapeutical treatment.