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September 2017

X-ray Footprinting Solves Mystery of Metal-Breathing Protein

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.

The research, led by scientists at the Molecular Foundry, 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 could also help researchers to understand and control the chemical reactions sparked by these protein-material interactions.

“Moving electrons to metals can cause different minerals to grow or dissolve. Studying how a protein does this can help us understand both how organisms remodel their environment and make biominerals for teeth or protection,” said Caroline Ajo-Franklin, a staff scientist in the Biological Nanostructures Facility at Berkeley Lab’s Molecular Foundry, which is a nanoscience research center.

Researchers relied on an X-ray-based technique at Berkeley Lab’s Advanced Light Source (ALS), known as “footprinting,” to pinpoint the chemical connections between the bacterial protein and nanoparticles composed of iron and oxygen.

The structure of this exotic protein had been previously mapped in isolation with atomic-scale detail by other research groups using X-ray crystallography, which required a crystallized form of the protein. But scientists didn’t know how it bound to the metal-containing mineral – conventional techniques can’t see this binding process.

The protein selected for the study is from a metal-reducing bacterium, Shewanella oneidensis, which “eats sugar and basically breathes minerals” when oxygen is unavailable, Ajo-Franklin noted. “One of the reason these organisms are so much fun to study is that they interact with a wide range of materials.”

Read the full press release.