The molecular mechanism of plant degradation of glyphosate was revealed

Schematic diagram of the mechanism of action of glyphosate-degrading enzymes Photo courtesy of Daron Hai

Glyphosate produces more than 700,000 tons a year, making it the most widely used and productive herbicide in the world. The weed resistance produced by glyphosate abuse and the potential threat to the ecological environment and human health are of great concern.

On May 29, Professor Guo Ruiting’s team from the School of Life Sciences of Hubei University and the State Key Laboratory of Biocatalysis and Enzyme Engineering jointly established by the Ministry of Provinces and Ministries published a latest research paper in the Journal of Hazardous Materials, which for the first time analyzed the reaction mechanism of aldehyde ketone reductase AKR4C16 and AKR4C17 from the source of Mango barnyard (a malignant rice field weed). And through molecular modification, the degradation efficiency of AKR4C17 on glyphosate was greatly improved.

Growing glyphosate resistance

Since its introduction in the 1970s, glyphosate has taken the world by storm and has gradually become the cheapest, most widely used and most productive broad-spectrum herbicide. It causes metabolic disorders and death in plants, including weeds, by specifically inhibiting the key 5-enolol pyruvylshikimate-3-phosphate synthase (EPSPS) that is key in plant growth and metabolism.

Therefore, cultivating glyphosate-resistant genetically modified crops and using them in the field with glyphosate is an important way to control weeds in modern agriculture.

However, with the widespread use and abuse of glyphosate, dozens of weeds have gradually evolved and developed high glyphosate tolerance.

In addition, glyphosate-resistant genetically modified crops cannot decompose glyphosate, resulting in glyphosate accumulating and transporting within crops, which is easy to spread through the food chain and endanger human health.

Therefore, there is an urgent need to mine genes that can degrade glyphosate in order to breed high-glyphosate-resistant genetically modified crops with low glyphosate residues.

Analyze the crystal structure and catalytic reaction mechanism of plant-derived glyphosate-degrading enzymes

In 2019, research teams in China and Australia identified for the first time two aldehyde ketone reductase AKR4C16 and AKR4C17 degrading glyphosate from glyphosate-resistant mangobaste. They use NADP+ as a cofactor to degrade glyphosate into non-toxic aminomethylphosphonic acid and glyoxylic acid.

AKR4C16 and AKR4C17 are the first reported glyphosate degradation enzymes produced by natural evolution of plants, in order to explore the molecular mechanism of its degradation of glyphosate, Guo Ruiting’s team through X-ray crystal diffraction technology, respectively, resolved the structure of these two enzymes and cofactor high resolution complexes, revealed the binding mode of glyphosate, NADP+ and AKR4C17 ternary complex, and proposed the catalytic reaction mechanism of AKR4C16 and AKR4C17 mediating glyphosate degradation.

Structure of AKR4C17/NADP+/glyphosate complex and glyphosate degradation reaction mechanism. Photo courtesy of Daron Hai

Molecular modification improves the degradation efficiency of glyphosate

After obtaining the fine three-dimensional structural model of AKR4C17/NADP+/glyphosate, Professor Guo Ruiting’s team further obtained a mutant protein AKR4C17F291D that greatly improved the degradation efficiency of glyphosate by 70% through enzyme structure analysis and rational design.

Analysis of AKR4C17 mutant degradation glyphosate activity. Photo courtesy of Daron Hai

“Our work reveals the molecular mechanism by which AKR4C16 and AKR4C17 catalyze glyphosate degradation, laying an important foundation for further engineering AKR4C16 and AKR4C17 to improve their degradation efficiency to glyphosate.” Dai Longhai, corresponding author of the paper and associate professor of Hubei University, said that they constructed the mutant protein AKR4C17F291D with improved degradation efficiency of glyphosate, which provided an important reference for cultivating high-glyphosate-resistant genetically modified crops with low glyphosate residues and the use of microbial engineered bacteria to degrade glyphosate in the environment.

It is reported that Guo Ruiting’s team has long been engaged in the study of the structure analysis and mechanism of biodegradable enzymes, terpenes synthases and drug target proteins of toxic and harmful substances in the environment. Li Hao, Associate Researcher Yang Yu and Lecturer Hu Yumei are the co-first authors of the paper, and Guo Ruiting and Dai Longhai are the co-corresponding authors. (Source: China Science Daily Li Chen)

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