Rubisco and Crop Output

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Structure

Rubisco is composed of 8 large subunits and 8 small subunits. The large subunits house the binding/active sites. In Rubisco, the active site of bonding is centered around a magnesium ion. However, depending on the organism, Rubisco can also have a different shape. The magnesium ion in the center binds with the lysine on the large subunit. This, in turn, further helps with the Calvin cycle. (Harel, et. al) “The types of residues involved are acidic residues that interact with Mg2+, basic residues and histidines that interact with phosphate and hydroxyl groups, polar residues that interact with hydroxyl groups, one hydrophobic residue, and backbone atoms of several residues.” (Harel, et. al)

Function

Rubisco or ribulose- 1,5- bisphosphate carboxylase oxygenase is an enzyme that is involved in photosynthesis in plants and is specifically found in chloroplasts. (Harel, et. al) Rubisco is used in the light dependent part of the Calvin cycle. In this cycle, it catalyzes the most important step of carbon fixation. It converts atmospheric carbon dioxide into useable sugar. It does this by using carbon dioxide to make an intermediate, and then finally, 3-Phosphoglycerate. Most all of this 3-Phosphoglycerate is recycled and able to use again. It adds carbons to ribulose bisphosphate and then cleaves the 6 carbons into 2 chains with 3 carbons. Rubisco can also help to oxidize RuBP, a sugar.

Effect on Crop Output

Scientists can and have used Rubisco to make advances in plant technology. With the ever-changing problems going on in this world, some plant proteins can help change food scarcity. Some plant proteins, including Rubisco, can be even more useful and sustainable than proteins found in animals. It also has a lot of nutritional value, along with amino acids. For example, lysine is the most common amino acid found. Lysine may reduce anxiety by blocking stress response receptors, and it can also improve the absorption/retention of calcium. “Highly purified RuBisCO is a tasteless, odourless white powder with a nutritional value reported to be equal to or superior to that of other food proteins. RuBisCO also possesses some desirable functional properties which might enable food processors to successfully incorporate the protein into a number of different food products (desserts, composite meat products, ice cream, beverages). Further developments are to come to test RuBisCO into food systems such as desserts / yogurt for texturing and flavouring improvements.” (van de Velde, et. al) Rubisco makes up around 50% of the protein in plant leaves, which attributes to the green color plants give off. This is because of the very high chlorophyll content found within Rubisco. Since it makes up so much of the protein in the leaves, Rubisco is very important in nutrition and as an ingredient. “The protein is also attractive due to its high nutritional values and in vitro digestibility. Furthermore, RuBisCo is a competitive source of bioactive peptides with opioid‐like, memory‐enhancing, appetite‐stimulating, antioxidative, and antihypertensive properties, demonstrating the wide range of food applications where RuBisCo can be utilized.” (Stefano, et. al)

Problems

The major problem researchers have been working to change with Rubisco is the oxygenation instead of the carboxylation. The reason this is a problem is because the plant has to fix this, making this issue energetically unfavorable, by losing around 30% of the plants ATP in that step. When Rubisco binds oxygen instead, crop yield becomes lower, this is because it only makes half the product amount of 3-Phosphoglycerate. This limits how many times a plant can undergo the Calvin Cycle to make sugar. When temperatures begin to increase it is even more of an inconvenience and much more difficult for a plant to fix this problem. If we can fix this issue, Rubisco can not only be more successful with photosynthesis, but extremely successful with changing crop growth and quantity. (Sharwood) “In recent times, major advances in Rubisco engineering have been achieved through improvement of our knowledge of Rubisco synthesis and assembly, and identifying amino acid catalytic switches in the L-subunit responsible for improvements in catalysis. in crops such as rice will require further advances in chloroplast bioengineering and Rubisco biogenesis.” (Sharwood) Carefully modifying genes in specific major functioning subunits can help change Rubisco to adjust the Calvin cycle and save ATP. This all starts in the chloroplasts, where Rubisco works. Improvements can also be made in C3 plants as well. They can be engineered to harvest Co2 as well, just like C4 plants. There are also alternative pathways that can be created to avoid oxygenation. (Sharwood)

Success of Rubisco

Success of Rubisco can be measured by the Michaelis constant of O2 and of Co2. RCA plays an important part in maintaining Rubisco activity. RCA is a nuclear gene that encodes a chloroplast protein. It is a member of the AAA(+) protein superfamily. Without RCA, plants would need a high amount of CO2 because Rubisco activity wouldn’t be maintained. Sugar phosphate molecules inhibit catalysis and prevent carbamylation. RCA removes these sugar phosphate molecules. “In most plants, RCA comprises two isoforms, an α isoform equipped with a C-terminal extension containing two cysteine residues that confer redox regulation and a shorter b isoform (Carmo-Silva et al., 2015). In Arabidopsis, the b isoform does not contain the redoxsensitive cysteine residues and is less sensitive to ADP inhibition (Carmo-Silva & Salvucci, 2013). However, the b form of tobacco RCA is sensitive to ADP inhibition, which may be explained by the absence of the α isoform (Carmo-Silva & Salvucci, 2013).” (Sharwood) In conclusion, there are other factors in plants that can be modified to generate more crop growth. However, being able to manipulate Rubisco is the most energetically effective and can make the most impact on crop output.

References

Alber, Birgit., et. al “A Short History of RubisCO: the Rise and Fall (?) of Nature's Predominant CO2 Fixing Enzyme.” Current Opinion in Biotechnology, Elsevier Current Trends, 29 Aug. 2017, www.sciencedirect.com/science/article/pii/S095816691730099X. (alber, et. al)

van de Velde, Fred., et. al “From Waste Product to Food Ingredient: The Extraction of Abundant Plant Protein RuBisCo.” New Food Magazine, 13 May 2011, www.newfoodmagazine.com/article/4461/from-waste-product-to-food-ingredient-the-extraction-of-abundant-plant-protein-rubisco/. (van de Velde, et. al)

Stefano, Elisa Di, et al. “Plant RuBisCo: An Underutilized Protein for Food Applications.” Journal of the American Oil Chemists' Society, John Wiley & Sons, Ltd, 12 Aug. 2018, aocs.onlinelibrary.wiley.com/doi/abs/10.1002/aocs.12104. (Stefano, et. al)

NIZO. “Abundant Plant Protein Extracted for Food Application.” NIZO Food Research, 20 June 2018, www.nizo.com/abundant-plant-protein-extracted-food-application/. (NIZO) Harel, Michal. et. Al “RuBisCO.” RuBisCO - Proteopedia, Life in 3D, proteopedia.org/wiki/index.php/Rubisco. (Harel, et. Al)

Portis, Archie R. “Rubisco Activase - Rubisco's Catalytic Chaperone.” Photosynthesis Research, U.S. National Library of Medicine, 2003, www.ncbi.nlm.nih.gov/pubmed/16245090. (Portis Jr.) Goodsell, David S. “PDB101: Molecule of the Month: Rubisco.” RCSB, Nov. 2000, pdb101.rcsb.org/motm/11. (Goodwill)

Carmo-Silva AE, Salvucci ME. 2013. The regulatory properties of Rubisco activase differ among species and affect photosynthetic induction during light transitions. Plant Physiology 161: 1645–1655.

Carmo-Silva E, Scales JC,Madgwick PJ, ParryMA. 2015.Optimizing Rubisco and its regulation for greater resource use efficiency. Plant, Cell & Environment 38: 1817–1832.

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