Researchers identify molecular 'culprit' in rise of planetary oxygen

Jan 10, 2012
University of Illinois crop sciences and Institute for Genomic Biology professor Gustavo Caetano-Anollés and his colleagues identified an oxygen-generating enzyme that likely was a key contributor to the rise of molecular oxygen on earth. Credit: L. Brian Stauffer

A turning point in the history of life occurred 2 to 3 billion years ago with the unprecedented appearance and dramatic rise of molecular oxygen. Now researchers report they have identified an enzyme that was the first – or among the first – to generate molecular oxygen on Earth.

The new findings, reported in the journal Structure, build on more than a dozen previous studies that aim to track the molecular evolution of life by looking for evidence of that history in present-day protein structures. These studies, led by University of Illinois crop sciences and Institute for Genomic Biology professor Gustavo Caetano-Anollés, focus on structurally and functionally distinct regions of proteins – called folds – that are part of the universal toolkit of living cells.

Protein folds are much more stable than the sequences of amino acids that compose them, Caetano-Anollés said. Mutations or other changes in sequence often occur without disrupting fold structure or function. This makes folds much more reliable markers of long-term evolutionary patterns, he said.

In the new study, Caetano-Anollés, working with colleagues in China and Korea, tackled an ancient mystery: Why did some of the earliest organisms begin to generate , and why?

"There is a consensus from earth scientists that about 2.4 billion years ago there was a big spike in oxygen on Earth," Caetano-Anollés said. They generally agree that this rise in oxygen, called the Great Oxygenation Event, was tied to the emergence of photosynthetic organisms.

"But the problem now comes with the following question," he said. "Oxygen is toxic, so why would a living organism generate oxygen? Something must have triggered this."

The researchers looked for answers in the "molecular fossils" that still reside in living cells. They analyzed protein folds in nearly a thousand organisms representing every domain of life to assemble a timeline of protein history. Their timeline for this study was limited to single-fold proteins (which the researchers believe are the most ancient), and was calibrated using microbial fossils that appeared in the geologic record at specific dates.

The analysis revealed that the most ancient reaction of aerobic metabolism involved synthesis of pyridoxal (the active form of vitamin B6, which is essential to the activity of many protein enzymes) and occurred about 2.9 billion years ago. An oxygen-generating enzyme, manganese catalase, appeared at the same time.

Other recent studies also suggest that aerobic (oxygen-based) respiration began on Earth 300 to 400 million years before the Great Oxidation Event, Caetano-Anollés said. This would make sense, since oxygen production was probably going on for a while before the spike in oxygen occurred.

Catalases convert hydrogen peroxide to water and oxygen. The researchers hypothesize that primordial organisms "discovered" this enzyme when trying to cope with an abundance of hydrogen peroxide in the environment. Some geochemists believe that hydrogen peroxide was abundant at this time as a result of intensive solar radiation on glaciers that covered much of Earth.

"In the glacial melt waters you would have a high concentration of hydrogen peroxide and that would be gradually exposing a number of the primitive organisms (alive at that time)," Caetano-Anollés said. The appearance of manganese catalase, an enzyme that degrades and generates oxygen as a byproduct, makes it a likely "molecular culprit for the rise of oxygen on the planet," he said.

Explore further: NASA balloons begin flying in Antarctica for 2014 campaign

More information: "Protein Domain Structure Uncovers the Origin of Aerobic Metabolism and the Rise of Planetary Oxygen," in journal Structure.

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kevinrtrs
1.4 / 5 (13) Jan 10, 2012
How did life arrive on the planet in the first place?

Unless and until that question gets answered all this kind of speculation about oxygen generation is just so much, well, speculation.

The use of vitamins is such a complex issue in any living organism that it could only have arisen by foresight, i.e. it needs to have been planned and orchestrated to completion beforehand. There's no way for it to have arisen by chance.

So there already is a strong indication that the origin of life on earth was not a chance event, but the result of an extremely complex and carefully designed construction.

As a result of such reasoning one can safely jump to the conclusion that the use of oxygen was a planned process, not something that happened serendipitously, as intimated in the article.
Deathclock
4.9 / 5 (7) Jan 10, 2012
How did life arrive on the planet in the first place?


Your question presupposes that "life" arrived here when it likely developed here instead. Further, you are also assuming that the concept of "alive" is actually a meaningful delimiter.

Is a self replicating protein alive?
Deathclock
4.9 / 5 (11) Jan 10, 2012
The use of vitamins is such a complex issue in any living organism that it could only have arisen by foresight, i.e. it needs to have been planned and orchestrated to completion beforehand. There's no way for it to have arisen by chance.

So there already is a strong indication that the origin of life on earth was not a chance event, but the result of an extremely complex and carefully designed construction.


This is just nonsense.

There was once a puddle that pondered the nature of it's existence. It determined that reality must have been designed to accommodate it, after all, it's hole fit it perfectly.

You're making the mistake that the environment was tailored for us rather than vice-versa. Much like a puddle is shaped by it's hole, we are shaped by our environment.

You are backwards and confused.
3432682
1 / 5 (4) Jan 10, 2012
Don't tell the EPA about the increase in oxygen.
Infinite Fractal Consciousness
5 / 5 (5) Jan 11, 2012
@kevinrtrs
Without evolution, how would you explain dog breeding, or bacteria becoming resistant to previously effective drugs, or the simple fact that kids look like their parents, or the domestication of plants, or the entire fossil record?
williamrmyers
5 / 5 (1) Jan 11, 2012
"Why did some of the earliest organisms begin to generate oxygen, and why?"

What?
gmurphy
not rated yet Jan 11, 2012
@williamrmyers, I think they meant 'when' and 'why'

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