War for Crops
Modern agriculture faces many challenges that cause significant crop losses every year. Sudden climate changes contribute not only to more frequent natural disasters but also to the spread of plant diseases and pests. Plant protection products are essential to maintaining healthy and abundant yields, but their use requires proper knowledge and caution to minimize negative impacts on the environment, humans, and beneficial organisms.
An increasing problem is the weeds resistant to currently used herbicides. As a result, many popular products lose effectiveness or are withdrawn from the market for safety reasons.
These challenges motivated research into previously uncharacterized metabolic pathways in plants. Further study and understanding of plant enzyme structures will allow identifying attractive molecular targets against which new, effective, and safe plant protection agents can be designed in the future.
X-ray crystallography allows us to look deeply into the protein structure, like through a powerful magnifying glass. Thanks to it, we learn the structure of enzymes and how they carry out chemical reactions.
Key Enzyme in Plant Metabolism
Our research focused on the enzyme ornithine transcarbamylase (OTC), which plays a key role in nitrogen metabolism in plants. We discovered how OTC opens and closes its catalytic center – the site where substrates bind and where chemical reactions occur. This enzyme is the target of bacteria from the genus Pseudomonas, which cause, among others, halo blight of bean – a disease leading to serious crop losses. Although this phenomenon is catastrophic for plants, a similar mechanism can be used to develop new herbicides effectively combating weeds.
The secret weapon of Pseudomonas syringae against OTC is a toxin called phaseolotoxin. It acts like a saboteur – blocking the OTC enzyme, a key enzyme in the arginine biosynthesis pathway, an amino acid essential for proper plant development and metabolism.
Structure of Plant OTC Enzyme Known for the First Time
Until now, the three-dimensional structure of OTC was known only in bacteria and animals. In our research, for the first time, we visualized the structure of this enzyme in plants. We discovered it contains a mobile fragment – the so-called SMG loop – which acts like a flap: opening and closing access to the enzyme’s active site. This movement stabilizes substrates in the catalytic center and allows product release.
Phaseolotoxin mimics the shape of the enzyme's natural substrates, perfectly fitting into the catalytic center. However, it binds to the enzyme much more strongly, so even after the center opens, it is not removed, effectively blocking the enzyme’s function and the entire metabolic pathway.
A Discovery That Could Change Crop Protection Strategy
Understanding the crystalline structures of plant OTC allowed us to grasp the precise mechanism of the enzyme and its interaction with the toxin, helping to explain how pathogens attack plants at the molecular level. Our knowledge of plant proteins is still incomplete, so every new piece of information is invaluable—especially for developing modern, selective plant protection products that can target key metabolic pathways and effectively block them.
Research Funding and Publication
The research was conducted under the SONATA project 2021/43/D/NZ1/00486 funded by the National Science Centre.
The results are described in the publication:
Nielipinski M, Pietrzyk-Brzezinska AJ, Wlodawer A and Sekula B (2023) Structural analysis and molecular substrate recognition properties of Arabidopsis thaliana ornithine transcarbamylase, the molecular target of phaseolotoxin produced by Pseudomonas syringae. Front. Plant Sci. 14:1297956. doi: 10.3389/fpls.2023.1297956.
The distinction of this work by the Crystallography Committee of the Polish Academy of Sciences emphasizes that modern research methods—such as protein crystallography—can have a significant impact on the development of agriculture and environmental protection, opening new possibilities for safer and more effective crop protection.