Kontinuierliche enzymatische Synthese von 2′-Desoxythymidin-5′-(α-D-glucopyranosyl)-diphosphat

Repetitive Batch Mode Facilitates Enzymatic Synthesis of the Nucleotide Sugars UDP-Gal, UDP-GlcNAc, and UDP-GalNAc on a Multi-Gram Scale

The availability of nucleotide sugars is considered as bottleneck for Leloir-glycosyltransferases mediated glycan synthesis. A breakthrough for the synthesis of nucleotide sugars is the development of salvage pathway like enzyme cascades with high product yields from affordable monosaccharide substrates. In this regard, the authors aim at high enzyme productivities of these cascades by a repetitive batch approach. The authors report here for the first time that the exceptional high enzyme cascade stability facilitates the synthesis of Uridine-5'-diphospho-α-d-galactose (UDP-Gal), Uridine-5'-diphospho-N-acetylglucosamine (UDP-GlcNAc), and Uridine-5'-diphospho-N-acetylgalactosamine (UDP-GalNAc) in a multi-gram scale by repetitive batch mode. The authors obtained 12.8 g UDP-Gal through a high mass based total turnover number (TTN_mass ) of 494 [g_product /g_enzyme ] and space-time-yield (STY) of 10.7 [g/L*h]. Synthesis of UDP-GlcNAc in repetitive batch mode gave 11.9 g product with a TTN_mass of 522 [g_product /g_enzyme ] and a STY of 9.9 [g/L*h]. Furthermore, the scale-up to a 200 mL scale using a pressure operated concentrator was demonstrated for a UDP-GalNAc producing enzyme cascade resulting in an exceptional high STY of 19.4 [g/L*h] and 23.3 g product. In conclusion, the authors demonstrate that repetitive batch mode is a versatile strategy for the multi-gram scale synthesis of nucleotide sugars by stable enzyme cascades.

An enzyme module system for the synthesis of dTDP-activated deoxysugars from dTMP and sucrose

A flexible enzyme module system is presented that allows preparative access to important dTDP-activated deoxyhexoses from dTMP and sucrose. The strategic combination of the recombinant enzymes dTMP-kinase and sucrose synthase (SuSy), and the enzymes RmlB (4,6-dehydratase), RmlC (3,5-epimerase) and RmlD (4-ketoreductase) from the biosynthetic pathway of dTDP-beta-L-rhamnose was optimized. The SuSy module (dTMP-kinase, SuSy, +/-RmlB) yielded the precursor dTDP-alpha-D-glucose (2) or the biosynthetic intermediate dTDP-6-deoxy-4-keto-alpha-D-glucose (3) on a 0.2-0.6 g scale with overall yields of 62 % and 72 %, respectively. A two-step strategy in which the SuSy module was followed by the deoxysugar module (RmlC and RmlD) resulted in the synthesis of dTDP-beta-L-rhamnose (4; 24.1 micromol, overall yield: 35.9 %). Substitution of RmlC by DnmU from the dTDP-beta-L-daunosamine pathway of Streptomyces peucetius in this module demonstrated that DnmU acts in vitro as a 3,5-epimerase with 3 as substrate to yield 4 (32.2 mumol, overall yield: 44.7 %). Chemical reduction of 3 with NaBH4 gave a mixture of the C-4 epimers dTDP-alpha-D-quinovose (6) and dTDP-alpha-D-fucose (7) in a ratio of 2:1. In summary, the modular character of the presented enzyme system provides valuable compounds for the biochemical characterization of deoxysugar pathways playing a major role in microbial producers of antibiotic and antitumour agents.

Purification of UDP-glucose pyrophosphorylase from germinated barley (malt)

UDP-glucose pyrophosphorylase was purified from germinated barley (malt) using anion exchange and hydrophobic interaction chromatography followed by preparative gel filtration. Gel filtration and SDS-PAGE revealed a molecular mass of 51 to 54 kDa for the monomeric protein. Microsequencing of the blotted protein by Edman degradation gave 20 N-terminal amino acids. UDP-glucose pyrophosphorylase from malt could be markedly stabilized by the addition of bovine serum albumin. The enzyme preparation is free of contaminating nucleoside triphosphatases (UTPases) and can be utilized for the enzymatic synthesis of activated sugars.