Clustered genes encoding 2-keto-L-gulonate reductase and L-idonate 5-dehydrogenase in the novel fungal D-glucuronic acid pathway

Joosu Kuivanen (Corresponding Author), Mikko Arvas, Peter Richard

Research output: Contribution to journalArticleScientificpeer-review

12 Citations (Scopus)

Abstract

D-Glucuronic acid is a biomass component that occurs in plant cell wall polysaccharides and is catabolized by saprotrophic microorganisms including fungi. A pathway for D-glucuronic acid catabolism in fungal microorganisms is only partly known. In the filamentous fungus Aspergillus niger, the enzymes that are known to be part of the pathway are the NADPH requiring D-glucuronic acid reductase forming L-gulonate and the NADH requiring 2-keto-L-gulonate reductase that forms L-idonate. With the aid of RNA sequencing we identified two more enzymes of the pathway. The first is a NADPH requiring 2-keto-L-gulonate reductase that forms L-idonate, GluD. The second is a NAD + requiring L-idonate 5-dehydrogenase forming 5-keto-gluconate, GluE. The genes coding for these two enzymes are clustered and share the same bidirectional promoter. The GluD is an enzyme with a strict requirement for NADP +/NADPH as cofactors. The k cat for 2-keto-L-gulonate and L-idonate is 21.4 and 1.1 s -1, and the K m 25.3 and 12.6 mM, respectively, when using the purified protein. In contrast, the GluE has a strict requirement for NAD +/NADH. The k cat for L-idonate and 5-keto-D-gluconate is 5.5 and 7.2 s -1, and the K m 30.9 and 8.4 mM, respectively. These values also refer to the purified protein. The gluD deletion resulted in accumulation of 2-keto-L-gulonate in the liquid cultivation while the gluE deletion resulted in reduced growth and cessation of the D-glucuronic acid catabolism.

Original languageEnglish
Article number225
Number of pages10
JournalFrontiers in Microbiology
Volume8
Issue numberFEB
DOIs
Publication statusPublished - 2017
MoE publication typeA1 Journal article-refereed

Keywords

  • fungi
  • Aspergillus
  • metabolism
  • D-glucuronate
  • D-glucuronic acid
  • L-idonate
  • 2-keto-L-gulonate

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