Cloning, expression, purification, crystallization and preliminary structure determination of glucose-1-phosphate uridylyltransferase (UgpG) from Sphingomonas elodea ATCC 31461 bound to glucose-1-phosphate

Two Homologous Enzymes of the GalU Family in Rhodococcus opacus 1CP-RoGalU1 and RoGalU2

Uridine-5’-diphosphate (UDP)-glucose is reported as one of the most versatile building blocks within the metabolism of pro- and eukaryotes. The activated sugar moiety is formed by the enzyme UDP-glucose pyrophosphorylase (GalU). Two homologous enzymes (designated as RoGalU1 and RoGalU2) are encoded by most Rhodococcus strains, known for their capability to degrade numerous compounds, but also to synthesize natural products such as trehalose comprising biosurfactants. To evaluate their functionality respective genes of a trehalose biosurfactant producing model organism—Rhodococcus opacus 1CP—were cloned and expressed, proteins produced (yield up to 47 mg per L broth) and initially biochemically characterized. In the case of RoGalU2, the V_max was determined to be 177 U mg⁻¹ (uridine-5’-triphosphate (UTP)) and K_m to be 0.51 mM (UTP), respectively. Like other GalUs this enzyme seems to be rather specific for the substrates UTP and glucose 1-phosphate, as it accepts only dTTP and galactose 1-phoshate in addition, but both with solely 2% residual activity. In comparison to other bacterial GalU enzymes the RoGalU2 was found to be somewhat higher in activity (factor 1.8) even at elevated temperatures. However, RoGalU1 was not obtained in an active form thus it remains enigmatic if this enzyme participates in metabolism.

Characterization of the biosynthetic pathway of nucleotide sugar precursor UDP-glucose during sphingan WL gum production in Sphingomonas sp. WG

To elucidate the possible biosynthetic pathway of a precursor UDP-glucose of the sphingan WL gum produced by Sphingomonas sp. WG, two enzymes phosphoglucomutase (PGM) and UDP-glucose pyrophosphorylase (UGPase) were bioinformatically analysed, expressed in Escherichia coli BL21 (DE3) and characterized. PGM was in the phosphoglucomutase/phosphomannomutase subclass and UGPase was predicted to be a UDP-glucose pyrophosphatase in a tetrameric structure. Both enzymes were expressed in soluble form, purified to near homogeneity with high activity at 1159 and 796 U/mg, exhibited folding with reasonable secondary structures, and existed as monomer and tetramer, respectively. The optimal pH and temperature of PGM were 9.0 and 50 °C, respectively, and this protein was stable at pH 8.0 and at temperatures ranging from 40 to 50 °C. The optimal pH and temperature of UGPase were 9.0 and 45 °C, respectively, and the protein was stable at pH 8.0 and at temperatures ranging from 30 to 55 °C. A small-scale one-pot biosynthesis of UDP-glucose by combining PGM and UGPase using glucose-6-phosphate and UTP as substrates was also performed, and formation of UDP-glucose was observed by HPLC detection, which confirmed the biosynthetic pathway of UDP-glucose in vitro. PGM and UGPase will be ideal targets for the metabolic engineering to improve WL gum yields in industrial production.

Cloning and characterization of CalS7 from Micromonospora echinospora sp. calichensis as a glucose-1-phosphate nucleotidyltransferase

The deoxysugar biosynthetic gene cluster of calicheamicin contains the calS7, which encodes glucose-1-phosphate nucleotidyltransferase and converts glucose-1-phosphate and nucleotides (NTP) to NDP-glucose and pyrophosphate. calS7 was expressed in Escherichia coli BL21(DE3), and the purified protein had significant thymidylyltransferase and uridylyltransferase activities as well, with some guanidylyltransferase activity but negligible cytidyl and adenyltransferase activity. The functions of thymidylyltransferase and uridylyltransferase were also verified using one-pot enzymatic synthesis of TMK and ACK. The products were analyzed by HPLC and ESI/MS, which showed peaks at m/z = 563 and 565 for TDP-D: -glucose and UDP-D-glucose, respectively, in negative mode.

The complex of Sphingomonas elodea ATCC 31461 glucose-1-phosphate uridylyltransferase with glucose-1-phosphate reveals a novel quaternary structure, unique among nucleoside diphosphate-sugar pyrophosphorylase members

Gellan gum is a widely used commercial material, available in many different forms. Its economic importance has led to studies into the biosynthesis of exopolysaccharide gellan gum, which is industrially prepared in high yields using Sphingomonas elodea ATCC 31461. Glucose-1-phosphate uridylyltransferase mediates the reversible conversion of glucose-1-phosphate and UTP into UDP-glucose and pyrophosphate, which is a key step in the biosynthetic pathway of gellan gums. Here we present the X-ray crystal structure of the glucose-1-phosphate uridylyltransferase from S. elodea. The S. elodea enzyme shares strong monomeric similarity with glucose-1-phosphate thymidylyltransferase, several structures of which are known, although the quaternary structures of the active enzymes are rather different. A detailed comparison between S. elodea glucose-1-phosphate uridylyltransferase and available thymidylyltransferases is described and shows remarkable structural similarities, despite the low sequence identities between the two divergent groups of proteins.

The molecular architecture of glucose-1-phosphate uridylyltransferase

Glucose-1-phosphate uridylyltransferase, also referred to as UDP-glucose pyrophosphorylase or UGPase, catalyzes the formation of UDP-glucose from glucose-1-phosphate and UTP. Not surprisingly, given the central role of UDP-glucose in glycogen synthesis and in the production of glycolipids, glycoproteins, and proteoglycans, the enzyme is ubiquitous in nature. Interestingly, however, the prokaryotic and eukaryotic forms of the enzyme are unrelated in amino acid sequence and structure. Here we describe the cloning and structural analysis to 1.9 A resolution of the UGPase from Escherichia coli. The protein is a tetramer with 222 point group symmetry. Each subunit of the tetramer is dominated by an eight-stranded mixed beta-sheet. There are two additional layers of beta-sheet (two and three strands) and 10 alpha-helices. The overall fold of the molecule is remarkably similar to that observed for glucose-1-phosphate thymidylyltransferase in complex with its product, dTDP-glucose. On the basis of this similarity, a UDP-glucose moiety has been positioned into the active site of UGPase. This protein/product model predicts that the side chains of Gln 109 and Asp 137, respectively, serve to anchor the uracil ring and the ribose of UDP-glucose to the protein. The beta-phosphoryl group of the product is predicted to lie within hydrogen bonding distance to the epsilon-nitrogen of Lys 202 whereas the carboxylate group of Glu 201 is predicted to bridge the 2'- and 3'-hydroxyl groups of the glucosyl moiety. Details concerning the overall structure of UGPase and a comparison with glucose-1-phosphate thymidylyltransferase are presented.