The Science

Bacteria that pump out manganese (Mn) oxide particles are skilled engineers. Producing these particles is a part of global cycles that move Mn through water, soil, vegetation, and more. How bacteria create the insoluble particles was poorly understood. Why? The enzymes involved were largely uncharacterized. A team revealed for the first time the structure of Mnx—a bacterial enzyme that mineralizes Mn—and the particles it produces.

The Impact

Better understanding these particle-forming enzymes could aid in engineering proteins to assist in transforming contaminants. Also, these insights could lead to bioenergy applications. The novel analytical tools used in this study could also solve the structure of other enzymes that play critical roles in global cycles. These tools could be especially useful in studying enzymes intractable by other approaches.

Summary

In numerous elemental cycles vital to life, Mn cycles between its reduced primarily soluble form (Mn(II)) and its oxidized insoluble forms (Mn(III,IV) oxides). Research has established Mn(II) is oxidized to Mn(III,IV) minerals primarily by bacteria and fungi. Yet, studying the biomineralization enzymes produced by these organisms is challenging because it is difficult to isolate and purify them. To address this challenge, researchers from the Oregon Health & Science University, the Ohio State University, and the Environmental Molecular Sciences Laboratory (EMSL) used state-of-the-art mass spectrometry, ion mobility, and electron microscopy to solve the previously uncharacterized structure of the enzyme complex Mnx and the Mn oxide nanoparticles it produces. The researchers used high-resolution mass spectrometry and atomic-resolution aberration-corrected scanning transmission electron microscopy at EMSL, a DOE Office of Science user facility. The data provide critical structural information for understanding Mn biomineralization, which is potentially well suited for environmental remediation applications. The technique used to characterize Mnx could be used on enzymes that are difficult to characterize with nuclear magnetic resonance, crystallography, or electron microscopy. Moreover, the new insights into the structure of the enzyme Mnx may inform ongoing research into the mechanisms of photosynthesis and catalytic oxygen production.

Funding

This work was supported by the Department of Energy’s (DOE’s) Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility. Part of the project was also funded by the National Science Foundation (NSF), the National Institutes of Health, and an NSF Postdoctoral Research Fellowship in Biology Award.

Publication

C.A. Romano, M. Zhou, Y. Song, V.H. Wysocki, A.C. Dohnalkova, L. Kovarik, L. Paša-Tolić, and B.M. Tebo, “Biogenic manganese oxide nanoparticle formation by a multimeric multicopper oxidase Mnx.” Nature Communications 8, 746 (2017). [DOI: 10.1038/s41467-017-00896-8]

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