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Substrate Diversity of L-Threonic Acid Dehydrogenase Homologs

C. F. Zhang1#, Y. P. Liu1#, X. X. Wu1, X. S. Zhang2,a*, and H. Huang1,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
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.
KEY WORDS: (R)-pantoate dehydrogenase, L-idonic acid catabolism, D-glucarate catabolism, L-altronic acid dehydrogenase, D-xylonic acid dehydrogenase

DOI: 10.1134/S0006297920040069