Novel Biological Mechanism Relays Electrons Along Hemes in Proteins in Mineral-Breathing Bacteria

Researchers simulating how certain bacteria run electrical current through tiny molecular wires have discovered a secret that nature uses for electron travel. The results are key to understanding how the bacteria do chemistry in the ground, and will help researchers use these bacteria in microbial fuel cells, batteries, or for turning waste into electricity. Within the bacteria's protein-based wire, molecular groups called hemes communicate with each other to allow electrons to hop along the chain like stepping stones. The researchers found that evolution has set the protein up so that, generally, when the electron's drive to hop is high, the heme stepping stones are less tightly connected, like being farther apart; when the drive to hop is low, the hemes are more closely connected, like being closer together. The outcome is an even electron flow along the wire. This is the first time scientists have seen this evolutionary design principle for electron transport, the researchers reported online on January 2, 2014 in PNAS. "We were perplexed at how weak the thermodynamic driving force was between some of these hemes," said geochemist Dr. Kevin Rosso of the Department of Energy's Pacific Northwest National Laboratory. "But it turns out those pairs of hemes are essentially hugging each other. When the driving force is strong between hemes, they are only shaking hands. We've never seen this compensation scheme before, but it seems that the purpose is to allow the protein to transfer electrons with a steady flow along heme wires." Certain bacteria breathe using metal like people use oxygen. In the process, these bacteria steal electrons from carbon and ultimately transfer the electrons to metals or minerals in the ground.
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