Another Missing Link is Good News and Bad News for Creationists

The enzyme rubisco is found in all plants and other photosynthesizing organisms. It plays a key role in fixing carbon from the air and has helped shape life on Earth. Now researchers at UC Davis, UC Berkeley and the Lawrence Berkeley National Lab have identified a new version of rubisco from environmental microorganisms dating back billions of years.

Credit: Getty Images

Study Finds Missing Link in the Evolutionary History of Carbon-Fixing Protein Rubisco | UC Davis.

Scientists at University of California, Davis have discovered another of these 'missing link' things that keep turning out to be not missing at all, but just not found until now. And it's good news and bad news for Creationists.

The good news is that it lets their putative creator god off the hook for designing what must be one of the worst examples of inept design in all of nature - the ubiquitous enzyme, found in all photosynthetic organisms, form I RuBisCo. The bad news is that it shows how form I RubisCo is the result of an evolutionary process and of course, it's another one of those pesky 'missing links' that are not supposed to be there if creationist dogma is correct.

RuBisCo is a major embarrassment for creationists because it is so inefficient. It is probably the least efficient enzyme there is. Paradoxically, it is it's inefficiency that makes it so abundant. To give it its full name, ribulose-1,5-bisphosphate carboxylase/oxygenase, has to make up in quantity what it lacks in quality because it can carry out only about 3 reactions a second, against the tens of thousands of reactions a second of most enzymes. It is the enzyme at the heart of photosynthesis that converts carbon dioxide, water and sunlight into glucose plus oxygen. As such it is the basis of almost all food pyramids and responsible for making the basic building blocks of plant cellulose and for supplying the oxygen in the atmosphere that almost everything needs for respiration.

But, not only is it incredibly slow at what it does but is often 'mistakes' a molecule of oxygen for a molecule of carbon dioxide and produces a bi-product that causes a destructive chain reaction that loses carbon and wastes energy. The reason for that is that it evolved in an oxygen-free environment where that mistake was not a problem. In fact, RubisCo is responsible for there being any oxygen in the atmosphere because it was the enzyme that the cyanobacteria contained that allowed them to use photosynthesis early in the history of life on Earth, giving rise to the first great mass extinction as the organisms that had evolved on an oxygen-free Earth were poisoned by oxygen. Most living organisms today are the descendants of survivors who learned to use oxygen.

Form I RubisCo is probably one of the most compelling arguments against intelligent design because it shows three things that cannot conceivably be thought of as the result of intelligent design:

1. Prolifically wasteful.
2. Massively inefficient.
3. An inability to scrap a bad design and start again.

In fact, I used the example of RuBisCo in my popular book, "The Unintelligent Designer: Refuting the Intelligent Design Hoax", which is now listed in the Cure For Christianity Library.

So, for those few creationists who are rightly embarrassed by RuBisCo because they know about it, it must come as a relief to be able to blame a natural, unguided, mindless process and not their favourite creator god's blundering ineptitude.

The bad news is, as I said above, that the research shows RuBisCo evolved out of a more primitive version early in the history of life on Earth and so amounts to one of those missing links that just shouldn't be there if Creationist dogma is right, and it shows how living systems progressed from simple beginnings to more complex ones.

As the UCDavis news item explains:

Form I rubisco evolved over 2.4 billion years ago before the Great Oxygenation Event, when cyanobacteria transformed the Earth’s atmosphere by producing oxygen through photosynthesis. Rubisco’s ties to this ancient event make it important to scientists studying the evolution of life.

In a study appearing Aug. 31 in Nature Plants, Banda and researchers from UC Davis, UC Berkeley and the Lawrence Berkeley National Laboratory report the discovery of a previously unknown relative of form I rubisco, one that they suspect diverged from form I rubisco prior to the evolution of cyanobacteria.

The new version, called form I-prime rubisco, was found through genome sequencing of environmental samples and synthesized in the lab. Form I-prime rubisco gives researchers new insights into the structural evolution of form I rubisco, potentially providing clues as to how this enzyme changed the planet.

An invisible world

Form I rubisco is responsible for the vast majority of carbon fixation on Earth. But other forms of rubisco exist in bacteria and in the group of microorganisms called Archaea. These rubisco variants come in different shapes and sizes, and even lack small subunits. Yet they still function.

3D images of the form I rubisco (left) compared to the newly discovered form I-prime (right).

“Something intrinsic to understanding how form I rubisco evolved is knowing how the small subunit evolved,” said Shih. “It’s the only form of rubisco, that we know of, that makes this kind of octameric assembly of large subunits.”

Study co-author Professor Jill Banfield, of UC Berkeley’s earth and planetary sciences department, uncovered the new rubisco variant after performing metagenomic analyses on groundwater samples. Metagenomic analyses allow researchers to examine genes and genetic sequences from the environment without culturing microorganisms.

“We know almost nothing about what sort of microbial life exists in the world around us, and so the vast majority of diversity has been invisible,” said Banfield. “The sequences that we handed to Patrick's lab actually come from organisms that were not represented in any databases.”

Banda and Shih successfully expressed form I-prime rubisco in the lab using E. coli and studied its molecular structure.

Form I rubisco is built from eight core large molecular subunits with eight small subunits perched on top and bottom. Each piece of the structure is important to photosynthesis and carbon fixation. Like form I rubisco, form I-prime rubisco is built from eight large subunits. However, it does not possess the small subunits previously thought essential.

“The discovery of an octameric rubisco that forms without small subunits allows us to ask evolutionary questions about what life would’ve looked like without the functionality imparted by small subunits,” said Banda. “Specifically, we found that form I-prime enzymes had to evolve fortified interactions in the absence of small subunits, which enabled structural stability in a time when Earth’s atmosphere was rapidly changing.”

According to the researchers, form I-prime rubisco represents a missing link in evolutionary history. Since form I rubisco converts inorganic carbon into plant biomass, further research on its structure and functionality could lead to innovations in agriculture production.

Greg Watry
Study Finds Missing Link in the Evolutionary History of Carbon-Fixing Protein Rubisco
UCDavis News - Science & Technology, Aug 31, 2020.

So, RuBisCo evolved very early in the history of life on Earth about 2.4 billion years ago, and diverged from this simpler 'missing link' before the cyanobacteria cause the 'Great Oxygenation Event'. This is exactly as predicted by the Theory of Evolution by natural Selection and completely at odds with what we would expect from an intelligent designer who supposedly created perfection as a one-off act of magic creation. Perhaps a creationist will be brave enough to attempt an explanation for a 'missing link' that isn't supposed to be there and for the ineptitude of any designer who designed RuBisCo.

Or maybe denialism is to be the order of the day again.

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