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Engineered Plant Enzyme Increases Carbon Dioxide Uptake

15 February 2006

Rubisco
RuBisCo catalyzes the rate-limiting step in biological carbon dioxide fixation. Source: Emory University

In research recently completed at Emory University School of Medicine, scientists have discovered a mutant enzyme that could enable plants to use and to convert carbon dioxide more quickly, effectively removing more greenhouse gasses from the atmosphere.

During photosynthesis, plants—and some bacteria—rely on the enzyme rubulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) to catalyze the rate-limiting step of the Calvin Cycle, the major pathway of carbon dioxide fixation. In other words, RuBisCO controls the rate at which plants can take up carbon dioxide from the atmosphere.

While RuBisCO is the most abundant enzyme in the world, it is also one of the least efficient.

All life pretty much depends on the function on this enzyme. It actually has had billions of years to improve, but remains about a thousand times slower than most other enzymes. Plants have to make tons of it just to stay alive.

—Dr. Ichiro Matsumura, senior author and principal investigator

For decades, scientists have struggled to engineer a variant of the enzyme that would more quickly convert carbon dioxide. Their attempts primarily focused on mutating specific amino acids within RuBisCO, and then seeing if the change affected carbon dioxide conversion. Because of RuBisCO’s structural complexity, the mutations did not have the desired outcome.

Previous attempts to improve the catalytic efficiency and/or CO2 specificity of RuBisCO by structure-based site-directed mutagenesis have at best led to modest (5–13%) improvements in specificity, according to the Emory team.

For the Emory study, Dr. Matsumura and his colleagues used directed evolution—isolating and randomly mutating genes, and then inserting the mutated genes into bacteria (in this case Escherichia coli, or E. coli). They then screened the resulting mutant proteins for the fastest and most efficient enzymes.

Because E. coli does not normally participate in photosynthesis or carbon dioxide conversion, it does not usually carry the RuBisCO enzyme. The scientists withheld other nutrients from the genetically modified bacteria so that it would need RuBisCO and carbon dioxide to survive under these stringent conditions.

The fastest growing strains carried mutated RuBisCO genes that produced a larger quantity of the enzyme, leading to faster assimilation of carbon dioxide gas. The RuBisCO variants that evolved during three rounds of random mutagenesis and selection were over-expressed, and exhibited 5-fold improvement in specific activity relative to the wild-type enzyme.

These mutations caused a 500 percent increase in RuBisCO expression. We are excited because such large changes could potentially lead to faster plant growth. This result also suggests that the enzyme is evolving in our laboratory in the same way that it did in nature.

—Dr. Matsumura

The findings were published online and in the February issue of the journal Protein Engineering Design and Selection.

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February 15, 2006 in Biotech, Climate Change, Emissions | Permalink | Comments (11) | TrackBack (3)

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Comments

Forget greenhouse gas reduction, this could revolutioinalize agriculture.

A very exciting development! Perhaps we aren't entirely doomed, yet...

Make me thought about something like:

Resident Evil: RuBisCO Enzyme

Detail: The entire city is mysteriously overrun by a invasive and highly aggresive plant overnight, a team of mercenary was air dropped in to find out what's going on. The encounter nothing else but zombie-like plants everywhere...

Ahh, forget about my last post its solely for fun only. Anyway it is an extremely exciting developement, 500 times faster! I just cant imagin how a sugar cane or oil palm that is 500 times more efficient can be. We can potentially use many hundreds times less agriculture land for entire world.

But a plant that is 500 times more efficient then the natural one, once it goes wild, the natural species stand almost no change at all.

500% faster = 5 times faster

Okay, so now we are going to have to disinfect our countertops and hands after touching plants too. They've just taken a bacteria that we are already fighting, and engineered it to survive and thrive quite well outside of any host.

Kudzu that grows 5 times faster?

VaP" Ummm, no they haven't. E. coli has been used as a lab organism for studying genetics and as a vehicle for cloning and mutation studies as long as that research has been carried out. At this moment probably thousands of college students are working with it in their undergraduate genetics classes - aside from all the petri dishes full of the stuff in university, government and industry labs.

The worry, as others have pointed out is the posibility of creating plants that become weeds and cause environmental problems down the line. Also, if you had fields of crops that were five times more efficient, nutrient cycling could become a problem. How do you supply enough macro and micro nutrients without polluting water supplies?

On the other, other hand if you could produce the same crops on one-fifth the land only the best farmland would remain in production and the more marginal or vulnerable land could be returned to prarie or forest.

"Okay, so now we are going to have to disinfect our countertops and hands after touching plants too. They've just taken a bacteria that we are already fighting, and engineered it to survive and thrive quite well outside of any host."

Don't be daft. I doubt the engineered E. coli could survive any length of time outside the host. The lab bugs are very different from the ones that cause infections. Why would any scientist work with an infectious bug, unless he absolutely had to? Also, a bug that can do photosynthesis won't need a host.

hi sir,
iam sathish from coimbatore,sir iam doing my biotechnology msc.sir iam interested in doing my work with rubisco sir.now, after collecting the information about rubisco,iam very much interested in proceeding my work,till now i have just checked the activity of plants,i.e how they respond,i have also done it with endangered species.sir if you could help me with some of your ideas it would be an advancement for me.waiting for your reply sir.thank you sir

Impressive work but I remain skeptical about the real usefulness of this. Growth of plant is not limited by CO2 supply but by nutriements and water supply. I am not sure that if the plant can convert more CO2 in C that it will grow faster or fix more C if you don't increase the amount of, N, P, K and H2O and don't forget : light. As a famous biologist said : "Everything in biologie makes sense in light of Evolution" so in clear why would evoltion have designed such a poorly effective enzyme to fix C ? to me the answer is simple : because if was not necessary to have a more efficient enzyme to thrive and probably because there were other limiting factors. I would be interested to have the opinion of someone knowleageable on the topic. Asides it is truly impressive that we are able to tune suche basic function of plants.

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