杏吧原创

A new way to make simple organic bubbles could provide fresh clues about how biological cells formed spontaneously on early Earth 鈥� and help efforts to generate synthetic life.

Protocells, the ancient ancestors of life today, may have been little more than simple, spherical compartments, enclosed by membranes and containing water and the molecules of life. But how these compartments 鈥� or 鈥渧esicles鈥� 鈥� came about is a mystery.

It is the ultimate 鈥渃hicken and egg paradox鈥�, says at the University of California, San Diego. The membranes found in modern cells self-assemble in water from molecules called lipids. But in all modern life forms, the proteins that generate lipids only work when embedded in a membrane. In other words, you need a membrane to make a membrane.

Now, Devaraj鈥檚 research group has found a way around this constraint. 鈥淲e basically just [place] some small molecules and DNA into a solution, and out come vesicles that are protein decorated,鈥� says Devaraj.

To perform this trick, the researchers relied on a 20-year-old technology developed to encourage naked DNA, removed from its cell, to still function and generate proteins. The approach involves placing the DNA in a solution with only the basic ingredients needed to translate a genetic code into a protein: 35 or so proteins, a dash of magnesium, a sprinkling of amino acids and other small molecules, plus a few ribosomes 鈥� the molecular 鈥渕achines鈥� inside cells where proteins are synthesised.

Devaraj鈥檚 group modified this system to generate one protein needed to create synthetic lipids and a second that can bind to the surface of the vesicles. When they add lipid precursors to the solution, vesicles form spontaneously in solution, and the second protein attaches to the outside of the membrane. This is the first time anyone has used this cell-free, DNA translation system to create a synthetic vesicle from scratch.

鈥淭o create them from scratch is really exciting,鈥� says at the University of Oxford, who wasn鈥檛 involved in the research. 鈥淚t鈥檚 just building down the complexity even more to simple starting materials.鈥�

That said, the system Devaraj and his colleagues used is still far too complex 鈥� and a few billion years too evolved 鈥� to mimic the emergence of the very first protocells on early Earth, according to at the University of California, Santa Cruz.

鈥淭he first membranes were simply mixtures of fatty acids and fatty alcohols,鈥� says Deamer. 鈥淵ou don鈥檛 need phospholipid membranes. That鈥檚 an evolutionary step up the complexity scale.鈥�

Devaraj agrees. He says that future versions of vesicles like those he and his colleagues have developed will be more useful for learning about living organisms in the deep past and today, rather than for understanding the origin of cellular life. 鈥淗ow is it that life can organise these molecules in a way that leads to these emergent phenomena like self-reproduction and self-repair and evolution?鈥� he says.

Booth says that any insights from these studies into the origin and organisation of life as we know it may also help in the efforts to generate synthetic life. 鈥淚f you can make vesicles, then you can think about making them make more vesicles. In which case, you can make things which are more life-like, synthetically,鈥� he says.

Devaraj says this is one of the real goals of his research. 鈥淯ltimately, that鈥檚 what we鈥檙e trying to strive toward. Can you take a known set of parts and assemble them spontaneously in a way that leads to a life-like artificial cell?鈥�

Although this might not help us solve the mystery of how, when or where life appeared, it might help us understand in a little more detail exactly what life needs to emerge and gain complexity. 鈥淚 think that鈥檚 what life has done, right? Across the billions of years,鈥� says Devaraj. 鈥淚t鈥檚 become more and more complicated.鈥�