Enzyme Module Systems for the Synthesis of Uridine 5′-Diphospho-α-D-glucuronic Acid and Non-Sulfated Human Natural Killer Cell-1 (HNK-1) Epitope

Tailor-made strategies for the stereo- and regioselective multi-step enzymatic synthesis of glycoconjugates require well characterized glycosyltransferases and carbohydrate modifying enzymes. We here report on a novel enzyme cascade for the synthesis of uridine 5'-diphospho-alpha-D-glucuronic acid (UDP-GlcA) and the non-sulfated human natural killer cell-1 (HNK-1) epitope including in situ regeneration of UDP-GlcA and the cofactor nicotinamide adenine dinucleotide NAD(+) by the combination of four enzymes in one-pot. In the first enzyme module sucrose synthase 1 (SuSy1) is used to produce uridine 5'-diphospho-alpha-D-glucose (UDP-Glc) from sucrose and uridine 5'-diphosphate (UDP). The combination with UDP-Glc dehydrogenase in the second enzyme module leads to the synthesis of UDP-GlcA with concomitant in situ regeneration of the cofactor NAD(+) by nicotinamide adenine dinucleotide hydride (NADH)-oxidase. In the third enzyme module the mammalian glucuronyltransferase GlcAT-P catalyzes the synthesis of the non-sulfated HNK-1 epitope by regioselective transfer of GlcA onto N-acetyllactosamine type 2 (LacNAc type 2). We present a comprehensive study on substrate kinetics, substrate specificities, variation and relation of enzyme activities as well as cross inhibition of intermediate products. With optimized reaction conditions we obtain superior product yields with streamlined synthesis costs for the expensive nucleotide sugar UDP-GlcA and cofactor NAD(+).