RuBisCO

The preprint, uh, I'm gonna suggest folks check out this month is, uh, from Jochen Sieges lab at UC Davis.

Uh, it's called De novo Rubisco design with protein language models.

Uh, this is a really, uh, great protein engineering paper on a very important problem, uh, that, uh, that is basically Rubisco, which is either the most abundant or one of the most abundant proteins, uh, on earth, uh, that is, uh, responsible for, uh, carbon fixation in, in plants and, and other photosynthetic organisms.

Um, the idea of designing, redesigning Rubisco in the face of rising, uh, CO2 is something that is very, uh, front of mind for a lot of plant scientists and people interested in, uh, climate change.

Um, and that is because Rubisco is sort of famously not the greatest enzyme in two ways.

Yeah.

It's, uh, it's not a very fast enzyme, and it is- has low specificity, um, for carbon dioxide versus oxygen.

This happens in three phases.

Phase one is carbon fixation, which is catalyzed by an enzyme called rubisco.

Rubisco captures CO2 from the atmosphere and attaches it to a five-carbon sugar called ribulose bisphosphate.

The resulting six-carbon molecule is unstable and splits into two molecules of three phosphoglycerate.

Phase two is reduction.

So in this cycle, carbon dioxide is fixed, meaning inorganic carbon dioxide gas is used to build the backbones of organic molecules.

An enzyme called Rubisco, this is probably my favorite enzyme name, helps combine carbon dioxide with a 5-carbon molecule, eventually leading to the production of glucose and other carbohydrates.

Now not all photosynthesis is the same.

We have oxygenic photosynthesis, which occurs in plants, algae, and cyanobacteria.

And I was able to find the direct quote that, uh, and I copied it and put it on my screen.

It says, "Corn hybrids that genetically block degradation of RuBisCO and PEP carboxylase are more resistant to stalk rot than normal hybrids." Well, what does that mean? Sounds, it's a lot of scientific jargon.

Well, essentially RuBisCO and PEP carboxylase are the two foundational enzymes that drive photosynthesis in the C4 photosynthetic pathway.

RuBisCO is the Calvin cycle and the PEP carboxylase is the C4 pathway that makes the corn plant so exceptionally efficient.

And, uh, translating all of that jargon into plain and simple English, this basically means that these two proteins, these two enzymes that are proteins, are tremendous stores of nitrogen inside the leaf and the stalk.

So if a hybrid lacks the, uh, genetic machinery or just genetically it isn't particularly effective at protecting those proteins from being degraded during grain fill, what happens during grain fill is that some genetics will move, will degrade those particular proteins, degrade those enzymes, and dismantle them, take them out of the stalk and out of the leaf and move them into the ear.

The starting materials? A mix of CO2 molecules from the air and preassembled molecules called ribulose bisphosphate, or RUBP, each containing five carbons.

The initiator? An industrious enzyme named Rubisco that welds one carbon atom from a CO2 molecule with the RUBP chain to build an initial six-carbon sequence.

That rapidly splits into two shorter chains containing three carbons each and called phosphoglycerates, or PGAs for short.

Enter ATP and another chemical called nicotinamide adenine dinucleotide phosphate, or just NADPH.