Structural Characterization of Streptococcus pneumoniae Serotype 9A Capsule Polysaccharide Reveals Role of Glycosyl 6-O-Acetyltransferase wcjE in Serotype 9V Capsule Biosynthesis and Immunogenicity
Structural Characterization of Streptococcus pneumoniae Serotype 9A Capsule Polysaccharide Reveals Role of Glycosyl 6-O-Acetyltransferase wcjE in Serotype 9V Capsule Biosynthesis and Immunogenicity
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DOI：
10.1074/jbc.m112.346924
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发表时间：
2012-04-20
影响因子：
4.8
通讯作者：
Nahm, Moon H.
中科院分区：
文献类型：
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作者：
Calix, Juan J.;Saad, Jamil S.;Nahm, Moon H.
假定的荚膜O-乙酰转移酶基因wcjE在各种肺炎链球菌血清型中高度保守，但该基因在荚膜生物合成和细菌适应性中的作用仍不清楚。表达肺炎球菌血清型9A的分离株来自表达wcjE相关血清型9V的前体，通过功能丧失突变为wcjE。为了确定9V wcjE的生物合成作用，我们表征了血清型9V和9A荚膜多糖（PS）的结构和血清学性质。NMR数据显示，9V和9A PS均由相同的五糖重复单元组成，如先前所报道的。然而，与先前关于9A PS缺乏任何O-乙酰化的研究形成鲜明对比，我们鉴定了9A PS中α-葡萄糖醛酸和α-葡萄糖的O-乙酰化。此外，9V PS还包含β-N-乙酰甘露糖胺的-CH 2 O-乙酰化，这种修饰在体外重组缺失wcjE后消失。我们还表明，血清分型血清和单克隆抗体特异性9V和9A结合胶囊PS在O-乙酸依赖性的方式。此外，与9A PS相比，来自用血清型9V PS免疫的人供体的IgG和较小程度的IgM显示出与9V更强的结合。我们得出结论，血清型9V wcjE介导β-N-乙酰甘露糖胺的6-O-乙酰化。这种PS修饰可以被免疫个体中的抗体选择性地靶向，从而鉴定出wcjE失活和血清型9A出现的潜在选择性优势。
The putative capsule O-acetyltransferase gene wcjE is highly conserved across various Streptococcus pneumoniae serotypes, but the role of the gene in capsule biosynthesis and bacterial fitness remains largely unclear. Isolates expressing pneumococcal serotype 9A arise from precursors expressing wcjE-associated serotype 9V through loss-of-function mutation to wcjE. To define the biosynthetic role of 9V wcjE, we characterized the structure and serological properties of serotype 9V and 9A capsule polysaccharide (PS). NMR data revealed that both 9V and 9A PS are composed of an identical pentasaccharide repeat unit, as reported previously. However, in sharp contrast to previous studies on 9A PS being devoid of any O-acetylation, we identified O-acetylation of alpha-glucuronic acid and alpha-glucose in 9A PS. In addition, 9V PS also contained -CH2 O-acetylation of beta-N-acetylmannosamine, a modification that disappeared following in vitro recombinatorial deletion of wcjE. We also show that serotyping sera and monoclonal antibodies specific for 9V and 9A bound capsule PS in an O-acetate-dependent manner. Furthermore, IgG and to a lesser extent IgM from human donors immunized with serotype 9V PS displayed stronger binding to 9V compared with 9A PS. We conclude that serotype 9V wcjE mediates 6-O-acetylation of beta-N-acetylmannosamine. This PS modification can be selectively targeted by antibodies in immunized individuals, identifying a potential selective advantage for wcjE inactivation and serotype 9A emergence.