Geobacter's pili conduct electrons along their length using the rings on aromatic amino acids, according to a study in mBio this week. Contrary to all other known forms of biological electron transport, in which electrons are carried by discrete entities and passed from one to another, Geobacter's pili have a core of aromatic amino acids that turn these hair-like appendages into functioning electron-carrying biological wires, adding credence to a controversial idea in biology.
"It's the aromatic amino acids that make it a wire," says lead author Derek Lovley. Lovley and his colleagues developed a strain of Geobacter, Aro-5, that lacked aromatic amino acids in parts of the pili implicated in electron conduction, replacing them with smaller, non-aromatic amino acids. Without the aromatic amino acids, Lovley says, the pili are nothing more than protein strings. Importantly, Aro-5's pili were complete with OmcS, a multi-heme c-type cytochrome essential for iron oxide reduction that was long suspected of carrying the electrons along the length of the pili. But the presence of working OmcS wasn't enough.
"We showed it's not good enough to just make the string - you've got to make a wire," says Lovley.
Click on the source link to read more on mBio's blog, mBiosphere.