Artificial killer cells mimic life as they wipe out opponents

Predatory protocells

Yan Qiao, Mei Li, Richard Booth and Stephen Mann/Predatory behaviour in synthetic protocell communities

By Emily Benson

Even artificial cells can be killers. Cell-like structures made in a lab have been designed to target and obliterate another population of protocells.

This mimics a crucial step on the path from the earliest __life to today’s elaborate global ecosystem: creatures eating one another.

The hope is that it could one day be developed into a new way for targeted drug delivery. And it might just help us understand how complex cellular communities first evolved.

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Protocells are thought to have been the microscopic precursors to living cells. Scientists build artificial versions of them from things such as fatty acids and proteins to study how __life might have originated on Earth.

Microscopic death match: killer cell (faint, bottom) breaks down large, green prey cell

Yan Qiao, Mei Li, Richard Booth and Stephen Mann/Predatory behaviour in synthetic protocell communities

One way to do that is to study interactions between different kinds of protocells, an area that has largely been neglected in favour of tinkering with individual protocells, says Stephen Mann at the University of Bristol, UK.

So he and his colleagues created a community of artificial cells to see if they could get them to display the classic ecological setup of predators and prey.

Protocell ecosystems

Eventually, his team hopes to build an intertwined community of even more types of artificial cells, all reacting to one another and passing information back and forth. This system could be used in medicine and materials science, Mann says. “Ultimately, our vision is to think about protocell ecosystems,” he says.

Others broadly support the approach. “There’s definitely sense in studying simple systems like protocells,” says Hagan Bayley at the University of Oxford. “But in the end, you’re going to have to build up the complexity if you want to imitate life, or understand life.”

To test the idea that protocells could interact, the researchers designed a death match between two protocell populations. The predator cells were positively charged droplets containing a protein-degrading enzyme.

Their prey, which were much larger than the predator cells, were negatively charged capsules of protein encircling a bit of DNA that the scientists included to see if a cellular payload could be transferred from the quarry to its killer.

After the cells were attracted to one another by their opposing charges, the enzyme from the predator cells “drilled” through the protein membrane of their victims. In cases when the killer cells outnumbered their prey by eight to one, they obliterated almost all of them in under an hour, sucking up DNA in the process.

Because they are capsules, protocells like these might someday prove useful in medicine, Mann says. They could, for example, be used to ferry drugs into your body, then release them when triggered, though it is likely to be decades before protocells might be advanced enough to actually hit pharmacy shelves, says Bayley.

Deceptive behaviour

The protocells created by Mann and his colleagues display habits, such as moving and eating one another, that you might expect to see from interacting, living beings.

But because they aren’t actually alive, their behaviour highlights how easily we might be deceived in our search for extraterrestrial life, says Steven Benner at the Foundation for Applied Molecular Evolution in Alachua, Florida.

“If you were to see that in a sample from Mars, people would be writing PhD dissertations about this being a life form,” he says.

While these protocells aren’t alive – they can’t replicate on their own and they don’t evolve – their predatory interactions suggest that competition between abiotic individuals is possible, says Neal Devaraj at the University of California, San Diego.

That brings the field one step closer to perhaps someday demonstrating protocell evolution and even artificial life, he says.

In the meantime, Devaraj says it would be interesting to see if the predator protocells could be made to go after their prey in a more targeted way, perhaps by recognising a biological signature. Such killer protocells could be used to battle particular disease-causing bacteria.

Journal reference: Nature Chemistry, DOI: 10.1038/nchem.2617

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