title: Metabolic pathway of 3,6-anhydro-D-galactose in carrageenan-degrading microorganisms.
abstract: Complete hydrolysis of κ-carrageenan produces two sugars, D-galactose and 3,6-anhydro-D-galactose (D-AnG). At present, however, we do not know how carrageenan-degrading microorganisms metabolize D-AnG. In this study, we investigated the metabolic pathway of D-AnG degradation by comparative genomic analysis of Cellulophaga lytica LIM-21, Pseudoalteromonas atlantica T6c, and Epulopiscium sp. N.t. morphotype B, which represent the classes Flavobacteria, Gammaproteobacteria, and Clostridia, respectively. In this bioinformatic analysis, we found candidate common genes that were believed to be involved in D-AnG metabolism. We then experimentally confirmed the enzymatic function of each gene product in the D-AnG cluster. In all three microorganisms, D-AnG metabolizing genes were clustered and organized in operon-like arrangements, which we named as the dan operon (3,6-d-anhydro-galactose). Combining bioinformatic analysis and experimental data, we showed that D-AnG is metabolized to pyruvate and D-glyceraldehyde-3-phosphate via four enzyme-catalyzed reactions in the following route: 3,6-anhydro-D-galactose → 3,6-anhydro-D-galactonate → 2-keto-3-deoxy-D-galactonate (D-KDGal) → 2-keto-3-deoxy-6-phospho-D-galactonate → pyruvate + D-glyceraldehyde-3-phosphate. The pathway of D-AnG degradation is composed of two parts: transformation of D-AnG to D-KDGal using two D-AnG specific enzymes and breakdown of D-KDGal to two glycolysis intermediates using two DeLey-Doudoroff pathway enzymes. To our knowledge, this is the first report on the metabolic pathway of D-AnG degradation.
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 790-784, South Korea. sblee@postech.ac.kr.|Graduate School of Engineering Mastership, Pohang University of Science and Technology, Pohang, 790-784, South Korea. sblee@postech.ac.kr.
authors.forename: Sun Bok
authors.initials: SB
authors.lastname: Lee
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 790-784, South Korea.
authors.forename: Jeong Ah
authors.initials: JA
authors.lastname: Kim
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 790-784, South Korea.
authors.forename: Hyun Seung
authors.initials: HS
authors.lastname: Lim
mesh_terms: D001711:Biotransformation; D002351:Carrageenan / Q000378:metabolism*; D000068016:Eubacteriales / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D041965:Flavobacteriaceae / Q000235:genetics / Q000378:metabolism*; D005690:Galactose / Q000031:analogs & derivatives* / Q000378:metabolism; D005986:Glyceraldehyde 3-Phosphate / Q000378:metabolism; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D005810:Multigene Family; D009876:Operon; D031161:Pseudoalteromonas / Q000235:genetics / Q000378:metabolism*; D019289:Pyruvic Acid / Q000378:metabolism
chemical_list: D005986:Glyceraldehyde 3-Phosphate; C117625:3,6-anhydrogalactose; D019289:Pyruvic Acid; D002351:Carrageenan; D005690:Galactose
keywords: 2-Keto-3-deoxy-D-galactonate; 3,6-Anhydro-D-galactose; Carrageenan; Dan operon; DeLey–Doudoroff pathway; Metabolic pathway