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The trigonelline degradation pathway yields its secrets

Researchers at Genoscope's Genomics Metabolics Mixed Research Unit recently elucidated the degradation pathway of trigonelline, a molecule naturally present in plants that ensures resistance to water stress (osmoprotective role). The study, published in PNAS, revealed previously unknown enzymes and metabolites.

Published on 31 August 2018

​Trigonelline (also known as 1-methylpyridinium-3-carboxylate) has drawn substantial attention over the past ten years for its pharmacological potential, but its role as a potential nutrient for bacteria has been known to microbiologists for much longer. Surprisingly though, no information on its degradation pathway was available in metabolics databases or in the scientific literature.

To fill that vacuum, researchers from Genoscope's Genomics Metabolics Mixed Research Unit used the model bacterium Acinetobacter baylyi ADP1 for which the genome sequence is available and their complete mutant strains library to identify the genes involved in trigonelline degradation.

Following the purification of recombinant enzymes, they used an untargeted liquid chromatography/mass spectrometry-based approach, the researchers were able to reconstitute the metabolic degradation pathway in vitro and characterize the enzymes, substrates and products. Two of them were previously unknown but identified by the team as the first intermediaries of this pathway, which ultimately results in the formation of succinate and methylamine. Thus, although starting somewhat from scratch, the researchers succeeded in establishing not only the order and the nature of reactions but also the intermediary metabolites of the trigonelline degradation pathway.

Despite structural similarities between trigonelline and nicotinate, the degradation of the former does not converge toward the latter, but instead reveals another method used by bacteria to cleave the pyridine ring.

The genes involved in the trigonelline degradation pathway were detected in numerous marine bacterial species. The researchers are now setting their sights on using genomics and transcriptomics data from the Tara Oceans project to determine the species using the trigonelline degradation pathway as well as their abundance and distribution. The team's objective with this second step is to evaluate the contribution of trigonelline to the geochemical recycling of carbon and nitrogen.

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