Methionine ligand lability of homologous monoheme cytochromes c

Study on potential microbial community to the waste water treatment from bauxite desilication process

Discharging waste water from the bauxite desilication process will bring potential environmental risk from the residual ions and organic compounds, especially hydrolyzed polyacrylamide. Characterization of the microbial community diversity in waste water plays an important role in the biological treatment of waste water. In this study, eight waste water samples from five flotation plants in China were investigated. The microbial community and functional profiles within the waste water were analyzed by a metagenomic sequencing method and associated with geochemical properties. The results revealed that Proteobacteria and Firmicutes were the dominant bacterial phyla. Both phylogenetical and clusters of orthologous groups' analyses indicated that Tepidicella, Paracoccus, Pseudomonas, and Exiguobacterium could be the dominant bacterial genera in the waste water from bauxite desilication process for their abilities to biodegrade complex organic compounds. The results of the microbial community diversity and functional gene compositions analyses provided a beneficial orientation for the biotreatment of waste water, as well as regenerative using of water resources. Besides, this study revealed that waste water from bauxite desilication process was an ideal ecosystem to find novel microorganisms, such as efficient strains for bio-desilication and bio-desulfurization of bauxite.

Determining Redox Potentials of the Iron-Sulfur Clusters of the AdoMet Radical Enzyme Superfamily

While protein film electrochemistry (PFE) has proven to be an effective tool in the interrogation of redox cofactors and assessing the electrocatalytic activity of many different enzymes, recently it has been proven to be useful for the study of the redox potentials of the cofactors of AdoMet radical enzymes (AREs). In this chapter, we review the challenges and opportunities of examining the redox cofactors of AREs in a high level of detail, particularly for the deconvolution of redox potentials of multiple cofactors. We comment on how to best assess the electroactive nature of any given ARE, and we see that when applied well, PFE allows for not only determining redox potentials, but also determining proton-coupling and ligand-binding phenomena in the ARE superfamily.

Directed evolution of cytochrome c for carbon-silicon bond formation: Bringing silicon to life

Enzymes that catalyze carbon-silicon bond formation are unknown in nature, despite the natural abundance of both elements. Such enzymes would expand the catalytic repertoire of biology, enabling living systems to access chemical space previously only open to synthetic chemistry. We have discovered that heme proteins catalyze the formation of organosilicon compounds under physiological conditions via carbene insertion into silicon-hydrogen bonds. The reaction proceeds both in vitro and in vivo, accommodating a broad range of substrates with high chemo- and enantioselectivity. Using directed evolution, we enhanced the catalytic function of cytochrome c from Rhodothermus marinus to achieve more than 15-fold higher turnover than state-of-the-art synthetic catalysts. This carbon-silicon bond-forming biocatalyst offers an environmentally friendly and highly efficient route to producing enantiopure organosilicon molecules.

Functionally Distinct Bacterial Cytochrome c Peroxidases Proceed through a Common (Electro)catalytic Intermediate

The diheme cytochrome c peroxidase from Shewanella oneidensis (So CcP) requires a single electron reduction to convert the oxidized, as-isolated enzyme to an active conformation. We employ protein film voltammetry to investigate the mechanism of hydrogen peroxide turnover by So CcP. When the enzyme is poised in the active state by incubation with sodium l-ascorbate, the graphite electrode specifically captures a highly active state that turns over peroxide in a high potential regime. This is the first example of an on-pathway catalytic intermediate observed for a bacterial diheme cytochrome c peroxidase that requires reductive activation, consistent with the observed voltammetric response from the diheme cytochrome c peroxidase from Nitrosomonas europaea (Ne), which is constitutively active and does not require the same one electron activation. Mutational analysis at the active site of So CcP confirms that the rate-limiting step involves a proton-coupled single electron reduction of a high valent iron species centered on the low-potential heme, consistent with the same mutation in Ne CcP. The pH dependence of catalysis for wild-type So CcP suggests that reduction shifts the pK(a)'s of at least two amino acids. Mutation of His81 in "loop 1", a surface exposed loop thought to shift conformation during the reductive activation process, eliminated one of the pH dependent features, confirming that the loop 1 shifts, changing the environment of His81 during the rate-limiting step. The observed catalytic intermediate has the same electron stoichiometry and similar pH dependence to that previously reported for Ne CcP, which is constitutively active and therefore hypothesized to follow a different catalytic mechanism. The prominent similarities between the rate-limiting steps of differing mechanistic classes of bCcPs suggest unexpected similarities in the intermediates formed.