Substrate Diversity of L-Threonic Acid Dehydrogenase Homologs

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C. F. Zhang^1#, Y. P. Liu^1#, X. X. Wu¹, X. S. Zhang^2,a*, and H. Huang^1,b*

¹Guangdong Provincial Key Laboratory of Biotechnology for Plant Development, School of Life Sciences, South China Normal University, Guangzhou, 510631 Guangdong, China

²Institute of Ecological Science, School of Life Sciences, South China Normal University, Guangzhou, 510631 Guangdong, China

^# These authors contributed equally to this study.

^* To whom correspondence should be addressed.

Received November 26, 2019; Revised January 7, 2020; Accepted January 21, 2020

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Despite physiological importance of aldonic sugar acids for living organisms, little is known about metabolic pathways of these compounds. Here, we investigated the functional diversity of homologs of L-threonic acid dehydrogenase (ThrDH; UniProt ID: Q0KBC7), an enzyme composed of two NAD-binding domains (PF14833 and PF03446). Ten ThrDH homologs with different genomic context were studied; seven new enzymatic activities were identified, such as (R)-pantoate dehydrogenase, L-altronic acid dehydrogenase, 6-deoxy-L-talonate dehydrogenase, L-idonic acid dehydrogenase, D-xylonic acid dehydrogenase, D-gluconic acid dehydrogenase, and 2-hydroxy-3-oxopantoate reductase activities. Two associated metabolic pathways were identified: L-idonic acid dehydrogenase was found to be involved in the degradation of L-idonic acid through oxidation/decarboxylation in Agrobacterium radiobacter K84, while 2-hydroxy-3-oxopantoate reductase was found to participate in D-glucarate catabolism through dehydration/cleavage in Ralstonia metallidurans CH34.

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KEY WORDS: (R)-pantoate dehydrogenase, L-idonic acid catabolism, D-glucarate catabolism, L-altronic acid dehydrogenase, D-xylonic acid dehydrogenase

DOI: 10.1134/S0006297920040069

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