Enzymatic synthesis and properties of glycoconjugates with legionaminic acid as a replacement for neuraminic acid
作者:D. C. Watson、S. Leclerc、W. W. Wakarchuk、N. M. Young
DOI:10.1093/glycob/cwq135
日期:2011.1.1
In addition to sialic acid, bacteria produce several other nonulosonic acids, including legionaminic acid (Leg). This has exactly the same stereochemistry as sialic acid, with the added features of 9-deoxy and 7-amino groups. In order to explore the biological effects of replacing sialic acid residues (Neu5Ac) in glycoconjugates with Leg in its diacetylated form, diacetyllegionaminic acid (Leg5Ac7Ac), we tested CMP-Leg5Ac7Ac as a donor substrate with a selection of bacterial and mammalian sialyltransferases. The CMP-Leg5Ac7Ac was synthesized in vitro by means of cloned enzymes from the bacillosamine portion of the Campylobacter jejuni N-glycan pathway and from the Leg pathway of Legionella pneumophila. Using fluorescent derivatives of lactose, Galβ1,4GlcNAcβ and T-antigen (Galβ1,3GalNAcα) as acceptors, we tested eight different sialyltransferases and found that the Pasteurella multocida PM0188h and porcine ST3Gal1 sialyltransferases were significantly active with CMP-Leg5Ac7Ac, showing ∼60% activity when compared with CMP-Neu5Ac. The Photobacterium α2,6 sialyltransferase was weakly active, with ∼6% relative activity. The Leg5Ac7Ac-α-2,3-lactose product was then tested as a substrate with six sialidases of viral, bacterial and mammalian origin. All showed much lower activities than with the corresponding sialic acid substrate, with the influenza virus N1 being the most active and human NEU2 being the least active. These results show the feasibility of producing glycoconjugates with Leg5Ac7Ac residues as the terminal sugars, which should display novel biological properties.
除硅醛酸外,细菌还产生其他几种非乌洛托品酸,包括军团酰胺酸(Leg)。这种酸的立体化学结构与硅藻酸完全相同,但增加了 9-脱氧基团和 7-氨基基团。为了探索用 Leg 的双乙酰化形式--双乙酰军团胺酸(Leg5Ac7Ac)--取代糖醛酸残基(Neu5Ac)对生物的影响,我们用细菌和哺乳动物的部分硅烷基转移酶测试了 CMP-Leg5Ac7Ac 作为供体底物的效果。CMP-Leg5Ac7Ac 是通过克隆空肠弯曲杆菌 N-聚糖途径中的巴基氨基部分和嗜肺军团菌途径中的酶在体外合成的。我们使用乳糖的荧光衍生物、Galβ1,4GlcNAcβ和T-抗原(Galβ1,3GalNAcα)作为受体,测试了八种不同的硅烷基转移酶,发现多杀性巴氏杆菌 PM0188h 和猪 ST3Gal1 硅烷基转移酶对 CMP-Leg5Ac7Ac 有显著的活性,与 CMP-Neu5Ac 相比,活性提高了 60%。光杆菌 α2,6硅烷基转移酶的活性较弱,相对活性为 6%。然后,Leg5Ac7Ac-α-2,3-乳糖产物作为底物与病毒、细菌和哺乳动物来源的六种硅烷基化酶进行了测试。结果表明,六种病毒、细菌和哺乳动物来源的半乳苷酸酶的活性都远远低于相应的半乳苷酸底物,其中流感病毒 N1 的活性最高,而人类 NEU2 的活性最低。这些结果表明了生产以 Leg5Ac7Ac 残基为末端糖的糖醛酸共轭物的可行性,这种共轭物应具有新的生物特性。