At the heart of almost every plant, algae, and blob of green pond squash on Earth is a molecular engine for harvesting sunlight. Its only emissions are oxygen – a gas we can all be very thankful for today.
Were it not for the evolution of this common type of photosynthesis (also known as oxygen), a complex life as we know it would almost certainly not have emerged, at least not in the form that he did.
But one knows for sure who should be thanked for such a precious gift. Most efforts to find out where an oxygen-depleting imaging system came from suggest about 2.4 billion years ago, a time that coincided with a flood. of oxygen pouring into our oceans and atmosphere.
More primary forms of photosynthesis appear to have existed, although the ability to extract oxygen from water would have marginalized phototropic organisms, making this version of oxygen production a late modification. .
Imperial College London molecular biologist Tanai Cardona argues that we may have all been wrong, suggesting that oxygen photosynthesis may have been around when life was just beginning about 3.5 billion years ago year.
“We had previously shown that the biological system for oxygen production, known as photosystem II, was very old, but so far it was not possible for us to put it on a life history timeline. , ”Cardona said.
Several years ago, Cardona and his colleagues compared genes in two distant bacteria; a man who was capable of photosynthesizing without oxygen, called Heliobacterium modesticaldum, and a phototropic microbe called cyanobacterium.
They were surprised to discover that despite the sharing of common ancestry billions of years ago, and because each bacterium harvested sunlight in different ways, it was a vital enzyme to their seemingly unconventional processes.
H. modesticaldum’s the ability to separate water strongly suggested that microbes may be able to generate oxygen from photosynthesis much faster than contemporary models suggested.
This latest study takes their research a step further, estimating the extent to which proteins essential for the II imaging system have evolved over the ages, allowing the team work out back to a moment in history when a functional version of the system could have arisen.
“We used a technique called Ancestral Sequence Reconstruction to predict protein sequences of ancestral photoynthetic proteins,” said the study’s first author, Thomas Oliver.
“These series will give us information about how the ancestral image system II would have worked and we were able to show that many of the key components necessary for the evolution of oxygen in the image system II can be found to the earliest stages in the evolution of the enzyme. “
As a point of comparison, the team applied the same mechanism to an enzyme that was known to be essential for life from the start, such as ATP synthase and RNA polymerase.
They found strong evidence that photosystem II has been around for as long as these ‘base’ enzymes, placing them among the microbial life forms that ever existed around 3.5 billion years ago.
“Now, we know that photosystem II shows patterns of evolution that are usually just attributed to the oldest known enzymes, which were essential for the evolution of life itself, “Cardona said.
It is just as well to study in the future how well these enzymes would work. Without signs of oxygen levels rising so far back in time, it does not appear to have been an efficient process or a process that was necessarily of great benefit.
But knowing the building blocks could affect the way we determine priorities in finding life on other planets, suggesting that oxygen could be on a planet that is only a billion years old. age to be signs of life.
The discovery also provides a starting point for researchers to design synthetic forms of photosynthesis.
“We now have a keen awareness of how photosynthetic proteins grow, adapt to a changing world, we can use ‘guided evolution’ to learn how to adapt them to make new types of chemistry, “says Cardona.
“We were able to develop imaging systems that could perform complex green and sustainable chemical reactions entirely under the power of light.”
This research was published in BBA-Bioenergetics.