4-Deoxy-l-erythro-5-hexoseulose Uronate (DEH) and DEH Reductase: Key Molecule and Enzyme for the Metabolism and Utilization of Alginate.

Shigeyuki Kawai,Wataru Hashimoto

doi:10.3390/molecules27020338

Shigeyuki Kawai, Wataru Hashimoto

Open Access

https://doi.org/10.3390/molecules27020338

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Abstract

4-Deoxy-l-erythro-5-hexoseulose uronate (DEH), DEH reductase, and alginate lyase have key roles in the metabolism of alginate, a promising carbon source in brown macroalgae for biorefinery. In contrast to the widely reviewed alginate lyase, DEH and DEH reductase have not been previously reviewed. Here, we summarize the current understanding of DEH and DEH reductase, with emphasis on (i) the non-enzymatic and enzymatic formation and structure of DEH and its reactivity to specific amino groups, (ii) the molecular identification, classification, function, and structure, as well as the structural determinants for coenzyme specificity of DEH reductase, and (iii) the significance of DEH for biorefinery. Improved understanding of this and related fields should lead to the practical utilization of alginate for biorefinery.

Highlights

Brown macroalgae that contain up to 40% of alginate are a promising carbon source for biorefinery due to their advantages over terrestrial biomass including, e.g., the lack of requirements for agricultural fertilizer, pesticides, freshwater, and arable land [1]
deoxy-L-erythro-5-hexoseulose uronate (DEH) is reduced to 2-keto-3-deoxy-D-gluconate (KDG) by DEH reductase, KDG is phosphorylated to 2-keto-3-deoxy-phosphogluconate (KDPG) by KDG kinase, and KDPG is cleaved into pyruvate and glyceraldehyde-3-phosphate (GAP) by KDPG aldolase [8,9,10]
The alginate-non-utilizing bacterium E. coli was used as a host for production of ethanol from brown macroalgae, with the bacterium engineered to permit the assimilation of alginate [47]

Summary

Introduction

Brown macroalgae that contain up to 40% of alginate are a promising carbon source for biorefinery due to their advantages over terrestrial biomass including, e.g., the lack of requirements for agricultural fertilizer, pesticides, freshwater, and arable land [1]. The same study showed that a markerless KdgF deletion mutant of E. coli ATCC 25922 resulted in >40% reduction, but not complete loss, of the growth rate compared with wild-type ATCC 25922 (0.49·h−1 for wild type vs 0.28·h−1 for the ∆kdgF strain) on endoacting polygalacturonate lyase-treated polygalacturonate (a main component of pectin) This supports the finding that DKI can be formed nonenzymatically in vivo and that KdgF facilitates the formation of DKI in vivo. Hobbs et al [6] concluded that KdgF catalyzes the conversion of pectin- and alginate-derived 4,5-unsaturated monouronates to linear ketonized forms, a step in uronate metabolism that was previously thought to be spontaneous. If the cyclic hemiacetal stereoisomers are its substrates, DEH reductase has to catalyze both dehydration and reduction Another possibility is that the hydration of DEH could occur reversibly (Figure 1), and the substrate is still DEH. This may be in accord with the higher Km of DEH compared to that of NADPH for DEH reductases A1-R (1930 vs. 9.55 μM) and A1-R’ (4790 vs. 15.5 μM) [18]

Reactivity of DEH with Specific Amino Groups

Structure of DEH Reductase

Yeast as a Host for Biorefinery to Utilize Alginate

Findings

Conclusions and Perspectives