Engineering cofactor supply and NADH-dependent D-galacturonic acid reductases for redox-balanced production of l-galactonate in Saccharomyces cerevisiae

  • D-Galacturonic acid (GalA) is the major constituent of pectin-rich biomass, an abundant and underutilized agricultural byproduct. By one reductive step catalyzed by GalA reductases, GalA is converted to the polyhydroxy acid l-galactonate (GalOA), the first intermediate of the fungal GalA catabolic pathway, which also has interesting properties for potential applications as an additive to nutrients and cosmetics. Previous attempts to establish the production of GalOA or the full GalA catabolic pathway in Saccharomyces cerevisiae proved challenging, presumably due to the inefficient supply of NADPH, the preferred cofactor of GalA reductases. Here, we tested this hypothesis by coupling the reduction of GalA to the oxidation of the sugar alcohol sorbitol that has a higher reduction state compared to glucose and thereby yields the necessary redox cofactors. By choosing a suitable sorbitol dehydrogenase, we designed yeast strains in which the sorbitol metabolism yields a “surplus” of either NADPH or NADH. By biotransformation experiments in controlled bioreactors, we demonstrate a nearly complete conversion of consumed GalA into GalOA and a highly efficient utilization of the co-substrate sorbitol in providing NADPH. Furthermore, we performed structure-guided mutagenesis of GalA reductases to change their cofactor preference from NADPH towards NADH and demonstrated their functionality by the production of GalOA in combination with the NADH-yielding sorbitol metabolism. Moreover, the engineered enzymes enabled a doubling of GalOA yields when glucose was used as a co-substrate. This significantly expands the possibilities for metabolic engineering of GalOA production and valorization of pectin-rich biomass in general.

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Author:Simon HarthGND, Jacqueline WagnerORCiD, Tamina Sens, Jun-yong Choe, Philipp BenzORCiDGND, Dirk Weuster-BotzORCiDGND, Igor-Mislav OrebORCiDGND
Parent Title (English):Scientific reports
Publisher:Macmillan Publishers Limited, part of Springer Nature
Place of publication:[London]
Document Type:Article
Date of Publication (online):2020/11/04
Date of first Publication:2020/11/04
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2023/02/13
Tag:Metabolic engineering; Oxidoreductases
Issue:art. 19021
Article Number:19021
Page Number:12
First Page:1
Last Page:12
This work was supported by the German Federal Ministry of Education and Research, grant numbers 031B0342B (to M.O.) and 031B0342C (to D.W.B.).
Open Access funding enabled and organized by Projekt DEAL.
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 54 Chemie / 540 Chemie und zugeordnete Wissenschaften
5 Naturwissenschaften und Mathematik / 57 Biowissenschaften; Biologie / 570 Biowissenschaften; Biologie
6 Technik, Medizin, angewandte Wissenschaften / 60 Technik / 600 Technik, Technologie
Licence (German):License LogoCreative Commons - Namensnennung 4.0