title: Mechanism and inhibition of human UDP-GlcNAc 2-epimerase, the key enzyme in sialic acid biosynthesis.
abstract: The bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE) plays a key role in sialic acid production. It is different from the non-hydrolyzing enzymes for bacterial cell wall biosynthesis, and it is feed-back inhibited by the downstream product CMP-Neu5Ac. Here the complex crystal structure of the N-terminal epimerase part of human GNE shows a tetramer in which UDP binds to the active site and CMP-Neu5Ac binds to the dimer-dimer interface. The enzyme is locked in a tightly closed conformation. By comparing the UDP-binding modes of the non-hydrolyzing and hydrolyzing UDP-GlcNAc epimerases, we propose a possible explanation for the mechanistic difference. While the epimerization reactions of both enzymes are similar, Arg113 and Ser302 of GNE are likely involved in product hydrolysis. On the other hand, the CMP-Neu5Ac binding mode clearly elucidates why mutations in Arg263 and Arg266 can cause sialuria. Moreover, full-length modelling suggests a channel for ManNAc trafficking within the bifunctional enzyme.
authors.affiliation: Department of Biotechnology, Hungkuang University, Taichung, Taiwan.|Taiwan Advance Biopharm (TABP), Inc., Xizhi City, New Taipei City, Taiwan.
authors.forename: Sheng-Chia
authors.initials: SC
authors.lastname: Chen
authors.affiliation: Department of Biotechnology, Hungkuang University, Taichung, Taiwan.|Taiwan Advance Biopharm (TABP), Inc., Xizhi City, New Taipei City, Taiwan.
authors.forename: Chi-Hung
authors.initials: CH
authors.lastname: Huang
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan.
authors.forename: Shu-Jung
authors.initials: SJ
authors.lastname: Lai
authors.affiliation: Department of Biotechnology, Hungkuang University, Taichung, Taiwan.|Taiwan Advance Biopharm (TABP), Inc., Xizhi City, New Taipei City, Taiwan.
authors.forename: Chia Shin
authors.initials: CS
authors.lastname: Yang
authors.affiliation: Department of Medical Research, Taichung Veterans General Hospital, Taichung, Taiwan.
authors.forename: Tzu-Hung
authors.initials: TH
authors.lastname: Hsiao
authors.affiliation: Department of Medical Research, Taichung Veterans General Hospital, Taichung, Taiwan.
authors.forename: Ching-Heng
authors.initials: CH
authors.lastname: Lin
authors.affiliation: Division of Critical Care &Respiratory Therapy, Department of Internal Medicine, Taichung Veterans General Hospital, Taichung, Taiwan.
authors.forename: Pin-Kuei
authors.initials: PK
authors.lastname: Fu
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan.
authors.forename: Tzu-Ping
authors.initials: TP
authors.lastname: Ko
authors.affiliation: Department of Biotechnology, Hungkuang University, Taichung, Taiwan.
authors.forename: Yeh
authors.initials: Y
authors.lastname: Chen
mesh_terms: D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D002238:Carbohydrate Epimerases / Q000037:antagonists & inhibitors / Q000737:chemistry; D020134:Catalytic Domain; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D003568:Cytidine Monophosphate / Q000031:analogs & derivatives / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000737:chemistry; D006801:Humans; D006860:Hydrogen Bonding; D006868:Hydrolysis; D007700:Kinetics; D008958:Models, Molecular; D019158:N-Acetylneuraminic Acid / Q000096:biosynthesis*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D012794:Sialic Acids / Q000737:chemistry; D014530:Uridine Diphosphate / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D012794:Sialic Acids; C561601:cytidine-5'-monophosphosialic acid; D014530:Uridine Diphosphate; D002238:Carbohydrate Epimerases; C100033:UDP acetylglucosamine-2-epimerase; D003568:Cytidine Monophosphate; D019158:N-Acetylneuraminic Acid