UDP-glucose dehydrogenase: Substrate binding stoichiometry and affinity

UDP-glucose dehydrogenase (UGDH) is (6, 7) show that the reaction of UGDH involves two successive oxidations to convert the 6Ј-hydroxyl of UDP-glucose to a carboxylate, together with the reduction of 2 molecules of NAD ϩ to NADH. In animals, it constitutes the unique pathway for glucuronate formation (8). Because glucuronate is a component of glycosaminoglycans (GAGs), the mutation inactivation of UGDH (sugarless) abolishes GAG assembly and, consequently, abolishes GAG-dependent growth factor signaling (9 -11). The primary structure of the mammalian enzyme was obtained from the protein sequence of bovine UGDH (12). The human gene was also recently cloned and assigned to chromosome 4p15.1 (13). It contains 12 exons, extends over 26 kb, and has one major transcription start site (14).GAG chains of proteoglycans and hyaluronan are ubiquitous components of extracellular matrix and pericellular spaces. There is a growing body of information on the implication of GAGs in cell behavior, including signal transduction, cell proliferation, spreading, migration, and cancer growth and metastasis (15-17). GAG synthesis is influenced by cytokines and growth factors. Transforming growth factor-␤ is the most potent stimulator of proteoglycan and GAG synthesis, including that of hyaluronan. Its action, however, depends on the cell type (18). The synthesis of GAGs is also modulated by oxygen cell status. Hypoxic endothelial cells and lung fibroblasts enhanced the heparan sulfate/chondroitin sulfate ratio, which led to an increase of basic fibroblast growth factor reactivity on the cell surface (19,20). It was also shown that the level of intracellular UDP-glucuronate could influence GAG synthesis (8). Interestingly, the human UGDH was shown to be an early response gene after interleukin-1 treatment of ocular fibroblasts (21), as well as an early androgen response gene in breast cancer (22).Although a clone of human UGDH has been reported (13, 15), specific catalytic residues are not yet available. Therefore, further characterization of the active sites of human UGDH is needed to elucidate the physiological nature of the UGDH. In the present study, we have identified an NAD ϩ -binding site using photoaffinity labeling and cassette mutagenesis to gain a deeper insight into the structural basis of human UGDH. For this study, a 1509-base pair gene that encodes human UGDH has been chemically synthesized and expressed in Escherichia coli as a soluble protein. Identification of the nucleotide-binding sites of a variety of proteins has been advanced by the use of nucleotide photoaffinity analogues that selectively insert * This work was supported by Grant 03-PJ1-PG3-20900-0047 from the Korea Health 21 R&D Project, Ministry of Health and Welfare, Korea (to S.-W. C.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.The nucleotide sequence (s)

Section: Discussionsupporting

confidence: 66%

Section: Discussionmentioning

confidence: 52%

Importance of Gly-13 for the Coenzyme Binding of Human UDP-glucose Dehydrogenase

Huh

Yoon²,

Lee

et al. 2004

“…Several reports have provided structural and enzymologic insights into UGDH function in multiple species (6,7,10,11,(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). In all cases the enzyme oxidizes UDP-glucose through two NAD ϩ -dependent electron transfers.…”

mentioning

confidence: 99%

UDP-glucose Dehydrogenase Activity and Optimal Downstream Cellular Function Require Dynamic Reorganization at the Dimer-Dimer Subunit Interfaces

Hyde¹,

Thelen²,

Barycki

et al. 2013

Background: UDP-glucose dehydrogenase (UGDH) mutants were engineered to perturb hexamer:dimer quaternary structure equilibrium. Results: Dimeric species of UGDH have reduced activity in vitro and in supporting hyaluronan production by cultured cells. Conclusion: Only dynamic UGDH hexamers support robust cellular function. Significance: Manipulation of UGDH activity by hexamer stabilization may offer new therapeutic options in cancer and other pathologies.

“…Kinetic studies of the bovine (12)(13)(14)(15)(16)(17)(18)(19)(20), streptococcal (21)(22)(23)(24), and plant (25,26) enzymes have been reported. All forms of the enzyme are known to catalyze the same reaction.…”

mentioning

confidence: 99%

Characterization of Human UDP-glucose Dehydrogenase

Sommer

Barycki

Simpson

2004

UDP-glucose dehydrogenase (UGDH) catalyzes two oxidations of UDP-glucose to yield UDP-glucuronic acid. Pathological overproduction of extracellular matrix components may be linked to the availability of UDP-glucuronic acid; therefore UGDH is an intriguing therapeutic target. Specific inhibition of human UGDH requires detailed knowledge of its catalytic mechanism, which has not been characterized. In this report, we have cloned, expressed, and affinity-purified the human enzyme and determined its steady state kinetic parameters. The human enzyme is active as a hexamer with values for Km and Vmax that agree well with those reported for a bovine homolog. We used crystal coordinates for Streptococcus pyogenes UGDH in complex with NAD+ cofactor and UDP-glucose substrate to generate a model of the enzyme active site. Based on this model, we selected Cys-276 and Lys-279 as likely catalytic residues and converted them to serine and alanine, respectively. Enzymatic activity of C276S and K279A point mutants was not measurable under normal assay conditions. Rate constants measured over several hours demonstrated that K279A continued to turn over, although 250-fold more slowly than wild type enzyme. C276S, however, performed only a single round of oxidation, indicating that it is essential for the second oxidation. This result is consistent with the postulated role of Cys-276 as a catalytic residue and supports its position in the reaction mechanism for the human enzyme. Lys-279 is likely to have a role in positioning active site residues and in maintaining the hexameric quaternary structure.