Sialic acids are important recognition sites in protein- and lipid-linked glycans of higher organisms and of select bacteria and protozoa. They are also prominent in human milk oligosaccharides. Defined sialo-oligosaccharides have interesting applications in chemical glycobiology and represent emerging ingredients for health-related nutrition. The growing demand for sialo-oligosaccharides has promoted developments in multidisciplinary carbohydrate synthesis, with approaches by cascade bio-catalysis having a leading role. The key synthetic step involves catalysis by sialyltransferases (EC 2.4.99.-) and consists in attaching sialic acid from a cytidine 5′-monophosphate-activated donor (CMP-sialic acid) to the nascent oligosaccharide acceptor. Sialyltransferases from bacteria, in general, show convenient properties for application (e.g., relative ease of recombinant production; high specific activity and operational stability). Here, we review salient characteristics of the bacterial sialyltransferases active on d-galactose- and N-acetyl-d-galactosamine-containing acceptors and highlight advances of their development into efficient biocatalysts. We also show integration of these sialyltransferases into multistep enzymatic cascades for sialo-oligosaccharide (e.g., sialyllactose) production from expedient substrates, using in situ formation of the CMP-sialic acid donor. We summarize functional parameters of the enzymes for CMP-sialic acid supply and analyze multi-enzymatic synthesis of sialo-oligosaccharides from a reaction engineering point of view. We discuss opportunities of sialyltransferase cascades for efficient sialo-oligosaccharide production in vitro and in vivo.

唾液酸是高级生物以及某些细菌和原生动物的蛋白质和脂质连接的聚糖中的重要识别位点。它们在人乳寡糖中也很显着。定义的唾液寡糖在化学糖生物学中具有有趣的应用，并代表了与健康相关的营养的新兴成分。对唾液寡糖的日益增长的需求促进了多学科碳水化合物合成的发展，其中级联生物催化的方法起着主导作用。关键的合成步骤涉及唾液酸转移酶（EC 2.4.99.-）的催化作用，该步骤包括将胞苷5'-单磷酸酯活化供体的唾液酸（CMP-唾液酸）连接到新生的寡糖受体上。通常，细菌的唾液酸转移酶显示出方便的应用特性（例如，重组生产相对容易；高比活度和操作稳定性）。在这里，我们回顾了活跃的细菌唾液酸转移酶的显着特征ð -galactose-和Ñ乙酰基d其发展的受体和突出前进到有效的生物催化剂含有-galactosamine-。我们还显示了这些唾液酸转移酶整合到多步酶联级联反应中，从现场用CMP-唾液酸供体形成的唾液寡糖（例如唾液乳糖）生产唾液寡糖。我们总结了用于CMP-唾液酸供应的酶的功能参数，并从反应工程学角度分析了唾液寡糖的多酶合成。我们讨论了有效的唾液寡糖生产在体外和体内唾液酸转移酶级联的机会。