"The question then is, what are the useful pieces and what's just junk?" he said. "When we looked at the pieces, we'd find something that looks like a transistor or we would find something that looks like a tuning capacitor for the dial, and we would categorize them into these different classes."
Sure enough, the scientists were able to pick out four useful pieces -- modules made up of around 60 to 100 amino acids. Each one can carry electrons or carry out reactions but uses different metals (such as copper, iron nickel or manganese) or puts those metals in different configurations.
The scientists think the oldest of the four is the one with a cube-shaped cluster of four irons and four sulfurs. That's because this subunit would be very handy for harvesting energy around hydrothermal vents, which are known to host lifelike chemical reactions even when living things aren't around. That kind of chemistry could have made it much easier for microbes with the right kinds of electron-shuttling proteins to thrive, the thinking goes.
These ideas will have to be tested further in the lab, Nanda said. In the meantime, the scientists expect there are more Lego-like subunits beyond the four they've identified.
"We really are only looking at a very small subset of proteins, the ones that are involved in electron transfer," Nanda said.
These smash-and-search methods could be used to find shared building blocks within other groups of proteins beyond the electron-transfer group, he added.
The scientists also want to chop up those four subunits of 60 to 100 amino acids and find even smaller, simpler essential pieces within them, he said. The simpler the unit, the closer it might be to those primordial proteins.
Beyond helping scientists understand the proteins from life's distant past, this research could one day help scientists develop proteins of the future.
Proteins are already being designed for industrial and therapeutic uses, but this new technology could improve the process, scientists said. It could even be used to design proteins that split water -- which could lead to a cheap way of generating clean-burning hydrogen fuel.
And as computers continue to shrink, specially designed electron-transfer proteins could potentially help engineers build smaller transistors and diodes and capacitors -- perhaps even find a way to make them self-assemble into circuits, Nanda said.
"Then you could start to make electronic circuits not by lithography and printing these things onto chips," he said, "but maybe have bacteria synthesizing small electrical circuits for you and doing these sorts of things in a sustainable way."
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