Cryo-EM Structure of the Mnx Protein Complex Reveals a Tunnel Framework for the Mechanism of Manganese Biomineralization.

The global manganese cycle relies on microbes to oxidize soluble Mn(II) to insoluble Mn(IV) oxides. Some microbes require peroxide or superoxide as oxidants, but others can use O directly, via multicopper oxidase (MCO) enzymes. One of these, MnxG from strain PL-12, was isolated in tight association with small accessory proteins, MnxE and MnxF.

Metallo-inhibition of Mnx, a bacterial manganese multicopper oxidase complex.

The manganese oxidase complex, Mnx, from Bacillus sp. PL-12 contains a multicopper oxidase (MCO) and oxidizes dissolved Mn(II) to form insoluble manganese oxide (MnO) mineral. Previous kinetic and spectroscopic analyses have shown that the enzyme's mechanism proceeds through an activation step that facilitates formation of a series of binuclear Mn complexes in the oxidation states II, III, and IV on the path to MnO formation.

Characterization of Zinc Carboxylates in an Oil Paint Test Panel.

Zinc (carboxylate) soaps, formed by reactions between zinc oxide (ZnO) and fatty acids in a drying oil, are known to cause deterioration in the paint layers of modern and contemporary oil paintings. This study investigates zinc carboxylates that developed in an oil painting test panel designed to mimic the aging and degradation encountered in actual works of art. Following accelerated and natural aging, protrusions were noted on the surface of the test panel.

Biogenic and Synthetic MnO Nanoparticles: Size and Growth Probed with Absorption and Raman Spectroscopies and Dynamic Light Scattering.

MnO nanoparticles, similar to those found in soils and sediments, have been characterized via their UV-visible and Raman spectra, combined with dynamic light scattering and reactivity measurements. Synthetic colloids were prepared by thiosulfate reduction of permanganate, their sizes controlled with adsorbates acting as capping agents: bicarbonate, phosphate, and pyrophosphate. Biogenic colloids, products of the manganese oxidase, Mnx, were similarly characterized.

Surface Induced Dissociation Coupled with High Resolution Mass Spectrometry Unveils Heterogeneity of a 211 kDa Multicopper Oxidase Protein Complex.

Manganese oxidation is an important biogeochemical process that is largely regulated by bacteria through enzymatic reactions. However, the detailed mechanism is poorly understood due to challenges in isolating and characterizing these unknown enzymes. A manganese oxidase, Mnx, from Bacillus sp.

Biogenic manganese oxide nanoparticle formation by a multimeric multicopper oxidase Mnx.

Bacteria that produce Mn oxides are extraordinarily skilled engineers of nanomaterials that contribute significantly to global biogeochemical cycles. Their enzyme-based reaction mechanisms may be genetically tailored for environmental remediation applications or bioenergy production. However, significant challenges exist for structural characterization of the enzymes responsible for biomineralization.

Tunable Biogenic Manganese Oxides.

Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnO ) is explored. Physical characterisation of MnO includes scanning and transmission electron microscopy, and X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopy. This characterisation reveals that the MnO materials share the structural features of birnessite, yet differ in the degree of structural disorder.

Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Coordinated Two-Stage Mn(II)/(III) and Mn(III)/(IV) Mechanism.

The bacterial manganese oxidase MnxG of the Mnx protein complex is unique among multicopper oxidases (MCOs) in carrying out a two-electron metal oxidation, converting Mn(II) to MnO nanoparticles. The reaction occurs in two stages: Mn(II) → Mn(III) and Mn(III) → MnO. In a companion study , we show that the electron transfer from Mn(II) to the low-potential type 1 Cu of MnxG requires an activation step, likely forming a hydroxide bridge at a dinuclear Mn(II) site.

Mn(II) Oxidation by the Multicopper Oxidase Complex Mnx: A Binuclear Activation Mechanism.

The bacterial protein complex Mnx contains a multicopper oxidase (MCO) MnxG that, unusually, catalyzes the two-electron oxidation of Mn(II) to MnO biomineral, via a Mn(III) intermediate. Although Mn(III)/Mn(II) and Mn(IV)/Mn(III) reduction potentials are expected to be high, we find a low reduction potential, 0.38 V (vs Normal Hydrogen Electrode, pH 7.

Copper Binding Sites in the Manganese-Oxidizing Mnx Protein Complex Investigated by Electron Paramagnetic Resonance Spectroscopy.

Manganese-oxide minerals (MnO) are widely distributed over the Earth's surface, and their geochemical cycling is globally important. A multicopper oxidase (MCO) MnxG protein from marine Bacillus bacteria plays an essential role in producing MnO minerals by oxidizing Mn(aq) at rates that are 3 to 5 orders of magnitude faster than abiotic rates. The MnxG protein is isolated as part of a multiprotein complex denoted as "Mnx" that includes accessory protein subunits MnxE and MnxF, with an estimated stoichiometry of MnxEFG and corresponding molecular weight of ≈211 kDa.

Biogenic Manganese-Oxide Mineralization is Enhanced by an Oxidative Priming Mechanism for the Multi-Copper Oxidase, MnxEFG.

In a natural geochemical cycle, manganese-oxide minerals (MnO ) are principally formed through a microbial process, where a putative multicopper oxidase MnxG plays an essential role. Recent success in isolating the approximately 230 kDa, enzymatically active MnxEFG protein complex, has advanced our understanding of biogenic MnO mineralization. Here, the kinetics of MnO formation catalyzed by MnxEFG are examined using a quartz crystal microbalance (QCM), and the first electrochemical characterization of the MnxEFG complex is reported using Fourier transformed alternating current voltammetry.

Mn(II) Binding and Subsequent Oxidation by the Multicopper Oxidase MnxG Investigated by Electron Paramagnetic Resonance Spectroscopy.

The dynamics of manganese solid formation (as MnOx) by the multicopper oxidase (MCO)-containing Mnx protein complex were examined by electron paramagnetic resonance (EPR) spectroscopy. Continuous-wave (CW) EPR spectra of samples of Mnx, prepared in atmosphere and then reacted with Mn(II) for times ranging from 7 to 600 s, indicate rapid oxidation of the substrate manganese (with two-phase pseudo-first-order kinetics modeled using rate coefficients of: k(1obs) = 0.205 ± 0.

Arsenite oxidase also functions as an antimonite oxidase.

Arsenic and antimony are toxic metalloids and are considered priority environmental pollutants by the U.S. Environmental Protection Agency.

Comparative genomic analysis of phylogenetically closely related Hydrogenobaculum sp. isolates from Yellowstone National Park.

We describe the complete genome sequences of four closely related Hydrogenobaculum sp. isolates (≥ 99.7% 16S rRNA gene identity) that were isolated from the outflow channel of Dragon Spring (DS), Norris Geyser Basin, in Yellowstone National Park (YNP), WY.

Mutants of the base excision repair glycosylase, endonuclease III: DNA charge transport as a first step in lesion detection.

Endonuclease III (EndoIII) is a base excision repair glycosylase that targets damaged pyrimidines and contains a [4Fe-4S] cluster. We have proposed a model where BER proteins that contain redox-active [4Fe-4S] clusters utilize DNA charge transport (CT) as a first step in the detection of DNA lesions. Here, several mutants of EndoIII were prepared to probe their efficiency of DNA/protein charge transport.