Abstract
Pentoses, including D-xylose, L-arabinose, and D-arabinose, are generally phosphorylated to D-xylulose 5-phosphate in bacteria and fungi. However, in non-phosphorylative pathways analogous to the Entner-Dodoroff pathway in bacteria and archaea, such pentoses can be converted to pyruvate and glycolaldehyde (Route I) or α-ketoglutarate (Route II) via a 2-keto-3-deoxypentonate (KDP) intermediate. Putative gene clusters related to these metabolic pathways were identified on the genome of Herbaspirillum huttiense IAM 15032 using a bioinformatic analysis. The biochemical characterization of C785_RS13685, one of the components encoded to D-arabinonate dehydratase, differed from the known acid-sugar dehydratases. The biochemical characterization of the remaining components and a genetic expression analysis revealed that D- and L-KDP were converted not only to α-ketoglutarate, but also pyruvate and glycolate through the participation of dehydrogenase and hydrolase (Route III). Further analyses revealed that the Route II pathway of D-arabinose metabolism was not evolutionally related to the analogous pathway from archaea.
Highlights
The breakdown of D-glucose is central for energy and biosynthetic metabolism throughout all domains of life
The “Route I” pathway of D-xylose and L-arabinose from bacteria and archaea[7,8,9] is completely homologous to the non-phosphorylative ED pathway, and the KDP intermediate is cleaved through an aldolase reaction to pyruvate and glycolaldehyde
In the “Route II” pathway of D-xylose[12,13,14], L-arabinose[15,16,17,18], and D-arabinose[19,20,21] from bacteria and/or archaea, the KDP intermediate is alternatively converted into α-ketoglutarate via α-ketoglutaric semialdehyde by KDP dehydratase (EC 4.2.1.141)[22] and αKGSA dehydrogenase (EC 1.2.1.26). αKGSA is a metabolic intermediate involved in D-galacturonic acid and hexaric acids (D-glucarate and D-galactarate) pathways from bacteria[23,24,25]
Summary
In the modified non-phosphorylative pathway of L-rhamnose and L-fucose from bacteria and/or archaea[26,27,28], each L-2-keto-3-deoxyrhamnonate (L-KDR) and L-2-keto-3-deoxyfuconate intermediate (L-KDF) is converted into pyruvate and lactate via (putative) 2,4-dioxo-pentanonate by the sequential actions of dehydrogenase and hydrolase (schematic reactions F and G, the “Route III” pathway). The numbers of protein superfamilies belonging to these metabolic enzymes are limited, and there is significant phylogenetic mosaicism between them (Fig. 1c)[10]. Based on these findings, we focused on the putative gene cluster(s) of Herbaspirillum huttiense IAM 15032 related to the Route II pathway of pentose metabolism. To the best of our knowledge, this is the first study to show that pentoses are metabolized through the non-phosphorylative Route III pathway, and that the non-phosphorylative D-arabinose pathway is operative in archaea[19,20,21], and in bacteria
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
