The Protocell Project
At the Los Alamos National Laboratory, scientists are trying to create life. No slimy blobs have yet oozed their way out of a beaker of primordial soup, but scientists are combining some of the most basic elements of life to see if they can make non-living chemistry behave in a life-like way. Cracking the mysterious barrier between life and non-life could give us a clue to how life originated on Earth, and how it might begin elsewhere in the universe.
|Hans Ziock of the Los Alamos National Laboratory.|
Astrobiology Magazine’s Leslie Mullen sat down with Hans Ziock of the Los Alamos Earth and Environmental Sciences Division to discuss the progress made so far, and the steps that still need to be taken for artificial life to arise in the lab.
Astrobiology Magazine (AM): In your experiment at Los Alamos, you’re trying to develop a protocell that has life-like properties. What are the first steps you must take to begin such a project?
Hans Ziock (HZ) : The idea for this project was put forward by Steen Rasmussen and Liaohai Chen and others. We asked ourselves, “What are the common features of life?” Life is an information-generating system, so you need a genetic component to carry information. In order to have information, you need a metabolism to generate it and you need an energy source. And certainly, in one form or another, you need a boundary/container. Then we asked ourselves, “What’s the simplest way to put those three components together?” We wanted to keep it as simple as possible so we didn’t have to deal with the many complex issues modern cells have.
The protocell we have designed has a boundary composed of amphiphilic molecules, molecules that have one end that likes water and another end that’s oily and does not like water. These molecules automatically self-assemble to form bilayers, the same sort of structures that make up the walls of your cells. The bilayer is a series of two amphiphile molecules back to back, with the water loving parts exposed to the outside water and the inside water, and the oily parts touching each other in between.
The bilayer is a sticky substance to which molecules with similar amphiphilic properties become stuck to, allowing the other components, the information, metabolism, and “food” molecules, to be gathered and concentrated.
In modern cells, the information molecule is DNA, which carries the code for building proteins that act as catalysts. But our information molecule doesn’t have to be decoded in order to be read, it directly participates in the metabolism.
|Amphiphiles self assemble to form a spherical container. |
Credit: Los Alamos National Laboratory
We start out with a uniform soup of all the dissolved components. As we shine light on the soup, a metabolism molecule absorbs that light and becomes excited. Our information molecule stabilizes the molecule that absorbed the light by donating an electron. The molecule stays in an excited stable state long enough for that excitation energy to be transferred to do something useful.
The useful property that we’ve accomplished is using that energy to break apart a molecule which forms another amphiphile molecule for the bilayer. So we feed it an oily resource molecule, and light energy is used to break that molecule in two. One piece becomes waste and the other piece becomes another component molecule for the bilayer. As the reaction repeats itself, eventually we form enough of these amphiphiles, or fatty acids, that they spontaneously form spherical containers.
This system uses an information molecule coupled with a metabolism, and together they produce containers. So we’ve tied the three key components together.
|The DNA molecule is composed of four bases – adenine, guanine, cytosine and thymine — attached to two sugar/phosphate backbones that form the spiral.|
As opposed to modern cells, where the bilayer separates the outside environment from the inside volume where all the chemistry happens, we have all our chemistry happening on the bilayer surface or inside the bilayer.
We still have more steps to do before we get one of these protocells to reproduce itself. But it would use the same sort of metabolism to reproduce the information, the genetic material. And the information molecule would be a DNA-like molecule that could replicate just like DNA replicates, by carrying information in the bases that it’s made of.
AM: What is the information molecule you’re using?
HZ: Our information molecule is a modified version of a nucleobase, one of the bases that participate in DNA. We’ve modified a guanine into an oxoguanine. The oxoguanine has the right redox potential to donate an electron to our metabolic photosensitizer to stabilize it after light has hit it so that we trap the energy. None of the standard bases are able to donate the electron, so we needed that modified base. But that modified base can form a chain of these molecules, and the chain could self-replicate using the same standard techniques that DNA uses.
Oxoguanine is actually found in our bodies. The base pairing is not quite as strong and you end up with more errors when you try to copy it, so our bodies actively remove it. We did have to do some additional chemistry to get the oxoguanine to stick to the molecule that absorbs light.
AM: What else in your experiment did you have to change from what would’ve been readily available on the early Earth?
HZ: We made the resource molecule, the one that is broken in two by the metabolism to make the components of the container. But those fatty acids occur on the Earth today. They’re one of the components we use to make soaps, and they can be synthesized under prebiotic conditions.
|How life originated is still an open question. Scientists are trying to determine what conditions were like on the early Earth to help solve that mystery.|
The whole system resides in a water environment. The only component that is out of the ordinary is our metabolic compound that soaks up the light energy. We’re using a ruthenium metal complex. That was a much more specific design, and there’s nothing like it in light chemistry today.
We chose particular compounds which we thought would have a good chance of doing what we wanted. Unlike nature, which had hundreds of millions of years to get life going, our project has been three years long, and we’re hoping to get a fourth year. Essentially we only get one trial, but probably there were billions or even trillions of little regions on the early Earth where these chemical reaction systems were happening. So you had a tremendous number of opportunities on the early Earth, as well as a tremendous amount of time to assemble something that works. It needs a lot of trial and error.
AM: What kind of light do you shine on the chemical soup?
HZ: We use visible light. We just chose that because it’s very easy to control — we can turn it on and off — and if we really want to we can choose a specific wavelength. For the origin of life, all the needed energy was available from the existing materials in the early Earth. The energy could also have been provided by light, but my own guess is early life used a chemical energy system, much like the black smokers on the ocean floor. They’re probably too hot to make early life, but there are similar sorts of vents that are cooler, and probably could generate a stable environment. Michael Russell at JPL has been a leader in proposing and pursuing these cooler vents as the incubator of life.
AM: Your experiment is about the earliest possible life based on photo energy, yet you believe early life was chemical-based. Isn’t that a contradiction?
HZ: No, as I said we’re just picking the easiest solution for us to implement.
|Black smoker hydrothermal vents with tubeworms living close by. The origin of life may have required the more stable environment of the ocean floor.|
AM: Which life would have done as well, wouldn’t it have?
HZ: But you need a stable environment for a fairly long time. We don’t know how transparent to light the Earth’s atmosphere was early on. If you were exposed to the atmosphere it was probably an unstable environment, whereas the ocean floor was probably a fairly stable environment. It’s protected from meteor impacts, more or less. There’s a huge area of ocean floor, so there are many places for these trials to take place, until one of them, by accident, got it right.
AM: Do you feel like you’ve created life in the lab?
HZ: Not yet, but we’re getting closer.
AM: What’s the dividing line?
HZ: We need to have a container produce another container with the same information molecule, using outside energy to drive the metabolic reaction. We’d like it to carry useful information rather than just one base. We’d even like to have a strand of information molecules so that we can form a complementary strand, so that we can reproduce the information over and over again.
We think we can do it because it’s based on the same chemistry that we already have done. But things are always more complicated than they appear. And the other thing to keep in mind is this would be an extraordinarily simple form of life. It demonstrates the principle, but we’re a long way from what modern life is capable of. It’s really just a first step.