X-ray Footprinting Solves Mystery of Metal-Breathing Protein

3D structural rendering of protein
Results from X-ray footprinting mass spectrometry (XFMS) experiments at Lawrence Berkeley National Laboratory’s (LBNL) Advanced Light Source, mapped out on these three-dimensional structural renderings of a protein, helped researchers identify where the protein binds with a mineral. Red areas indicate possible binding areas. [Reprinted with permission from Fukushima, T., et al. “The Molecular Basis for Binding of an Electron Transfer Protein to a Metal Oxide Surface.” J. Am. Chem. Soc. 139(36), 12647–12654, (2017). [DOI:10.1021/jacs.7b06560]. Copyright (2017) American Chemical Society.]
Scientists have discovered the details of an unconventional coupling between a bacterial protein and a mineral that allows the bacterium to breathe when oxygen is not available. This research could lead to new innovations in linking proteins to other materials for bio-based electronic devices, such as sensors that can diagnose disease or detect contaminants. It also could help researchers to understand and control the chemical reactions sparked by these protein-material interactions and, eventually, how organisms remodel their environment and make biominerals.

Researchers relied on an X-ray-based technique known as “footprinting” to pinpoint the chemical connections between the bacterial protein and nanoparticles composed of iron and oxygen. The study identified a previously mapped, surprisingly small and weak binding site, but unknown was how the site bound to the metal-containing mineral because conventional techniques can’t see this binding process. Footprinting reveals interactions of proteins in a near-native environment. The protein selected for the study is from the metal-reducing bacterium Shewanella oneidensis, which “eats sugar and basically breathes minerals” when oxygen is unavailable. This study already is providing ideas on how to redesign these proteins to make better electronic connections and thus more sensitive bioelectronic sensors.

Fukushima, T., et al. “The Molecular Basis for Binding of an Electron Transfer Protein to a Metal Oxide Surface.” J. Am. Chem. Soc. 139(36), 12647–12654, (2017). [DOI:10.1021/jacs.7b06560].

Instruments and Facilities Used: X-ray beamline 5.3.1 of the Advanced Light Source (ALS) to perform “footprinting” and mass spectrometry at the Biological Nanostructures Facility at the Molecular Foundry, both at Lawrence Berkeley National Laboratory (LBNL), and the LBNL-led DOE Joint BioEnergy Institute.

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