Structure of the first purified manganese oxidase Mnx
EMSL Project ID
50914
Abstract
Microbial production of manganese oxide (MnO2) is a globally important biomineralization process. MnO2 is a key component of the Mn cycle, which supports life through the Mn catalytic centers of many enzymes, and by serving as an electron sink for microbial metabolism in the absence of O2. Microorganisms that produce MnO2 are widespread in nature and greatly accelerate the rate of Mn oxidation relative to uncatalyzed oxidation. Genetic evidence from many model systems for Mn(II)-oxidizing bacteria implicate multicopper oxidases (MCOs) to be the catalysts for Mn(II) oxidation and MnO2 formation. However, MCOs catalyze one-electron oxidation reactions, whereas conversion of Mn(II) to MnO2 is a two-electron process. How does nature harness a one-electron oxidase in a two-electron biomineralization process? Determining the mechanism by which different microbes oxidize and biomineralize manganese has been hindered by the difficulty of purification of intrinsic enzymes that carry out this complex process. However, the Tebo lab has recently succeeded in producing active Mn oxidase from marine Bacillus sp. strain PL-12 in E. coli by co-expressing three out of the four genes in the polycistronic mnx operon. The enzyme, which we call Mnx, is the first purified manganese oxidase, and it is solely responsible for both Mn oxidation and MnO2 mineral formation. Mnx is a complex of MnxG (138 kDa), a multicopper oxidase, tightly associated with three copies each of two small (12 kDa) accessory proteins MnxE and MnxF. Our system, the manganese-oxidizing MCO complex Mnx, has opened a new chapter in bioinorganic chemistry and provided the first opportunity for studying the molecular mechanisms by which MCOs catalyze the formation of MnO2 minerals. Significant progress toward characterization of the active enzyme, its MnO2 product, and the mechanism of Mn(II) oxidation has been made, but the molecular-level structural details of the enzyme are still missing. The objective of this project is to obtain high-resolution atomic structure of the first purified manganese-oxidizing complex, Mnx. The cryo-EM studies of Mnx structure determination will offer the essential protein structure information to complete our view of the mechanism of bacterial manganese biomineralization at the molecular level, expanding our knowledge of an important class of enzymes, MCOs, and their role in environmental processes. It will also lead to unraveling the biochemical mechanism of bacterial Mn oxidation and bring us closer to understanding the role of microbes in the biogeochemical cycling of Mn.
Project Details
Start Date
2019-06-15
End Date
2020-01-31
Status
Closed
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