Bacteria that produce manganese (Mn) oxides are extraordinarily skilled engineers of nanomaterials that contribute significantly to global biogeochemical cycles. However, mineralization mediated by these organisms is poorly understood because enzymes involved in these processes are largely uncharacterized. A recent study revealed for the first time the structure of Mnx — a bacterial enzyme complex responsible for Mn biomineralization — and the Mn oxide nanoparticles it produces.
An improved understanding of biomineralization enzymes may allow scientists to engineer proteins for applications such as environmental remediation and bioenergy production. The novel analytical tools used in this study could also be applied to solve the structure of other enzymes that play a critical role in global biogeochemical cycles, especially enzymes intractable by more conventional nuclear magnetic resonance, crystallography, or electron microscopy approaches.
Mn is a very important transition metal for all life. Mn cycling between its reduced primarily soluble form (Mn(II)) and its oxidized insoluble forms (Mn(III,IV) oxides) is coupled in myriad ways to many elemental cycles. Research has established Mn(II) is oxidized to Mn(III,IV) minerals primarily through activities of bacteria and fungi. Yet, the biomineralization enzymes produced by these organisms are very challenging to study 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 EMSL, the Environmental Molecular Sciences Laboratory, used state-of-the-art mass spectrometry, ion mobility, and electron microscopy to solve the previously uncharacterized structure of 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. These data provide critical structural information for understanding Mn biomineralization, which is potentially well suited for environmental remediation applications. Moreover, the new insights into the structure of Mnx may inform ongoing research into the mechanisms of photosynthesis and catalytic oxygen production.