Neu5Ac transferase

In this technique, the enzyme solution is put inside a dialysis bag which is then immersed in a solution of substrate, or cofactors. Small molecules can diffuse through the wall of the bag and react in the presence of the enzyme, while products, if also small molecules, diffuse into the outside solution, where they may be recovered. This technique has been used in syntheses with sialyl aldolase, Kdo-synthetase, the common aldolase, a mixture of hexokinase and pyruvate kinase, a-(2— 6) sialyl transferase,26 a mixture of pyruvate kinase and adenylate kinase,27 and CMP-Neu5Ac synthetase.28... 

Most sialylations so far reported have been achieved with soluble transferases, and seldom on a more than 20-/imol scale (see Table IX), with the intention to prepare and describe sequences present in glycoproteins and glycolipids. Trisaccharide < -D-Neu5Ac-(2— 3)-/J-D-Galp-(l — 3)-/J-d-... 

Following the enzymatic synthesis of CMP-Neu5Ac, isolated a2-6-sialyl-transferases could be used to introduce sialic acid to the N-acetyl lactosamine derivates a-f in position 6. This afforded a series of trisaccharide derivates Neu5Aca2-6 Gal l-4GlcNAc l-R. The unblocked trisaccharide a [55], the methyl glycoside b [56], the -Asn derivative c [57], the pentapeptide derivative d [58], the allyl e [59], and the pent-4-enyl glycoside f [48] can be prepared in convincing yields (Fig. 6). 

Introduction of a fluoride at the 3-position of neuraminic acid yielded a compound (57) that was a competitive inhibitor of the a-(2,6)-sialyl-trans-ferase. Base and sugar-modified analogues of CMP-Neu5Ac have also been prepared to investigate the tolerance of oc-(2,6)-sialyl-transferase to base exchange (58) and modification of the 5-, 8- or 9-position of neuraminic acid (59), (60). While base-exchange was not tolerated, modifications of the acid moiety yielded compounds that were substrates for the enzyme. 

Biosynthetic studies using CMP-[ C]Neu5Ac indicated that there are three sialyl-transferase activities responsible for the assembly of the polysialylglycan chains of PSGP ... 

Sialic Acid. CTP CMP-Neu6Ac Synthetase Neu5Ac(a2 3) Transferase... 

Scheme 13. Chemoenzymatic synthesis of N-Trocprotected sialylated lactosamine donor 34. CMP-NeuSAc synthetase (29) and Neu5Ac(a2- 3)transferase (30) are known enzymes.

A large number of enzymes are glycoproteins. These belong mainly to the oxidoreductases, transferases and hydrolases. About 50% of the glycoprotein enzymes have sialic acid as Neu5Ac and Neu5Gc (Jutisz and De la Llosa 1972, Bahl and Shah 1977). 

This chapter will describe several Leloir-type transferase reactions that have been used for stepwise construction of a oligosaccharides comprising five different monosaccharides, GlcNAc, GalNAc, Gal, Fuc, and Neu5Ac. This is a very limited approach among the myriads of possible oligosaccharides that can be potentially... 

Several a3-sialyltransferases have been cloned, and ST3Gal III is commercially available in recombinant form. A particularly interesting report of Gilbert et al. [55] describe a fusion protein consisting of CMP-Neu5Ac synthetase and o2,3-sialyl-transferase from Neisseria meningitidis. This polypeptide was able to catalyze the reactions shown in eqs (2) and (3). 

Neu5Ac and Neu5Gc were the preferred nonulosonic acid substrates for the calf brain CMP-Sia synthetase. Thus, mammalian CMP-Sia synthetases recognized similar, yet distinctively different, substrate specificity determinants. The expression of CMP-KDN synthetase was shown to be temporally correlated with development, and to parallel the developmental expression of (KDN)GM3 in sperm. The enzyme was used to synthesize CMP-[ C]-KDN, which was characterized by NMR (Terada et al., 1993), and to identify and characterize a CMP-KDN a2,8-KDN transferase, as described below. 

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