Sialyltransferases donor specificity

The Brossmer and Paulson groups have studied the sialyltransferase donor specificity with a series of C5 and C9 conjugates, all of which were prepared through the CMP-... 

In contrast to the acceptor specificity, the donor specificity of sialyltransferases is less pronounced, although differences exist. They can transfer not only Neu5Ac but... 

Another multifunctional bacterial enzyme that has been reported recently is Pasteurella multocida sialyltransferase (PmSTl or tPm0188Ph) (67, 68). It has four different activities, including an a2,3SiaT, a2,6SiaT, a2,3-sialidase, and trans-sialidase activities. PmSTl is a highly active sialyltransferase with broad donor and acceptor substrate specificity therefore it is a powerful tool... 

In order to prepare o2,6-linked sialoside libraries with naturally occurring and non-natural sialic acid modifications, a flexible o2,6-sialyltransferase enzyme is required. Although several manunalian sialyltransferases have been reported to have relatively broad donor substrate specificity (for example, rat liver o2,6-sialyltransferases can tolerate a variety of modifications on the Neu5Ac moiety of CMP-Neu5Ac) (29-32), but they suffer from low expression level which limits their applications in preparative- and large- scale synthesis of sialosides. 

The H3a,3e/NAc structural reporters of NeuSAc have proved to be suitable in studying sialylation reactions in terms of positional specificity and branching (N-linked carbohydrate chains) specificity, using different sialyltransferases and CMP-NeuSAc as donor [333-335] (see also section 6.3). 

Notes and discussion. A major drawback of enzymatic sialylation with sialyl-transferases is the strict acceptor specificity of these enzymes. This synthesis addresses this limitation by showing a widely applicable transfer of sialic acid (NeuAc) from a donor substrate of the sequence NeuAca-(2 —3)Gal-ORi to virtually any galactose acceptor (Gal-OR2). This method uses the less substrate specific glycosidase from Trypanosoma cruzi. The problem with this method is that the product is made at the expense of another sialoside, used as the donor substrate, and as NeuAc transfer is a reversible process, it is difficult to drive the equilibrium in favour of the desired sialoside. For this reason the sialoside donor substrate is regenerated in situ by an a-(2 3)-sialytransferase enzyme, thus enhancing the production of the desired product. The specificity of the sialyltransferase ensures that only the galactose byproduct, formed from the sialyl donor, is re-sialyated as the Gal-OR2 acceptor substrate is a poor substrate. Due to the broad specificity of the trans-sialidase, many a-NeuAc-(2 3)-Gal-OR sequences can be synthesised by... 

Sialyltransferases. In eukaryotic cells, addition of terminal sialic acid to glycoconjugates is carried out by specific enzymes called sialyltransferases (STs). STs catalyze the transfer of a sialic acid from the activated nucleotide sugar donor CMP-N-acelylneuraminic acid (CMP-NeuSAc) to the terminal nonreducing position of oligosaccharide chains either of glycoproteins or glycolipids. 

H. Yu, S. Huang, H. Chokhawala, M. Sun, H. Zheng, X. Chen, Highly efficient chemoenzy-matic synthesis of naturally occurring and non-natural a-2,6-linked sialosides a P. damsela a-2,6-sialyltransferase with extremely flexible donor-substrate specificity, Angew. Chem. Int. 45 (2006) 3938-3944. 

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