Abstract
A novel metabolic pathway of 3,6-anhydro-l-galactose (l-AHG), the main sugar component in red macroalgae, was first discovered in the marine bacterium Vibrio sp. EJY3. l-AHG is converted to 2-keto-3-deoxy-galactonate (KDGal) in two metabolic steps. Here, we identified the enantiomeric nature of KDGal in the l-AHG catabolic pathway via stereospecific enzymatic reactions accompanying the biosynthesis of enantiopure l-KDGal and d-KDGal. Enantiopure l-KDGal and d-KDGal were synthesized by enzymatic reactions derived from the fungal galacturonate and bacterial oxidative galactose pathways, respectively. KDGal, which is involved in the l-AHG pathway, was also prepared. The results obtained from the reactions with an l-KDGal aldolase, specifically acting on l-KDGal, showed that KDGal in the l-AHG pathway exists in an l-enantiomeric form. Notably, we demonstrated the utilization of l-KDGal by Escherichia coli for the first time. E. coli cannot utilize l-KDGal as the sole carbon source. However, when a mixture of l-KDGal and d-galacturonate was used, E. coli utilized both. Our study suggests a stereoselective method to determine the absolute configuration of a compound. In addition, our results can be used to explore the novel l-KDGal catabolic pathway in E. coli and to construct an engineered microbial platform that assimilates l-AHG or l-KDGal as substrates.
Key points
• Stereospecific enzyme reactions were used to identify enantiomeric nature of KDGal
• KDGal in the l-AHG catabolic pathway exists in an l-enantiomeric form
• E. coli can utilize l-KDGal as a carbon source when supplied with d-galacturonate
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All data generated or analyzed during this study are included in this published article and its supplementary information file.
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Funding
This work was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry, and Fisheries funded by the Ministry of Agriculture, Food, and Rural Affairs (32136-05-1-SB010) and the Ministry of Trade, Industry and Energy (20018132). KHK also received grant supports from Korea University and the Institute of Biomedical Science and Food Safety at the Korea University Food Safety Hall, Korea University. EJY acknowledges a grant support from the National Research Foundation of Korea (RS-2023-00247769).
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EJY and KHK conceived and designed the research. EJY, SY, DHK, and NJP the conducted experiments. EJY and JJL analyzed the data. EJY wrote the manuscript. YSJ and KHK revised the manuscript. All authors read and approved the manuscript.
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Yun, E.J., Yu, S., Kim, D.H. et al. Identification of the enantiomeric nature of 2-keto-3-deoxy-galactonate in the catabolic pathway of 3,6-anhydro-l-galactose. Appl Microbiol Biotechnol 107, 7427–7438 (2023). https://doi.org/10.1007/s00253-023-12807-7
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DOI: https://doi.org/10.1007/s00253-023-12807-7