Engskog Mikael K R, Yildirim Håkan H, Li Jianjun, Richards James C, Deadman Mary, Hood Derek W, Schweda Elke K H
Clinical Research Centre, Karolinska Institutet and Södertörn University, NOVUM, S-141 86 Huddinge, Sweden.
Carbohydr Res. 2009 Mar 31;344(5):632-41. doi: 10.1016/j.carres.2009.01.005. Epub 2009 Jan 17.
Lipopolysaccharide (LPS) of Haemophilus influenzae comprises a conserved tri-l-glycero-d-manno-heptosyl inner-core moiety (l-alpha-d-Hepp-(1-->2)-[PEtn-->6]-l-alpha-d-Hepp-(1-->3)-[beta-d-GlcIp-(1-->4)]-l-alpha-d-Hepp-(1-->5)-alpha-Kdop) to which addition of beta-d-Glcp to O-4 of GlcI in serotype b strains is controlled by the gene lex2B. In non-typeable H. influenzae strains 1124 and 2019, however, a beta-d-Galp is linked to O-4 of GlcI. In order to test the hypothesis that the lex2 locus is involved in the expression of beta-d-Galp-(1-->4-beta-d-Glcp-(1--> from HepI, lex2B was inactivated in strains 1124 and 2019, and LPS glycoform populations from the resulting mutant strains were investigated. Detailed structural analyses using NMR techniques and electrospray-ionisation mass spectrometry (ESIMS) on O-deacylated LPS and core oligosaccharide material (OS), as well as ESIMS(n) on permethylated dephosphorylated OS, indicated both lex2B mutant strains to express only beta-d-Glcp extensions from HepI. This provides strong evidence that Lex2B functions as a galactosyltransferase adding a beta-d-Galp to O-4 of GlcI in these strains, indicating that allelic polymorphisms in the lex2B sequence direct alternative functions of the gene product.
流感嗜血杆菌的脂多糖包含一个保守的三 - l - 甘油 - d - 甘露庚糖基内核部分（l - α - d - Hepp - (1→2)-[PEtn→6]-l - α - d - Hepp - (1→3)-[β - d - GlcIp - (1→4)]-l - α - d - Hepp - (1→5)-α - Kdop），在b型菌株中，向GlcI的O - 4位添加β - d - Glcp受基因lex2B控制。然而，在不可分型的流感嗜血杆菌菌株1124和2019中，一个β - d - Galp连接到GlcI的O - 4位。为了检验lex2基因座参与β - d - Galp - (1→4)-β - d - Glcp - (1→从HepI表达的假说，在菌株1124和2019中使lex2B失活，并研究所得突变菌株的脂多糖糖型群体。使用核磁共振技术和电喷雾电离质谱（ESIMS）对O - 去酰化脂多糖和核心寡糖物质（OS）进行详细的结构分析，以及对全甲基化去磷酸化OS进行串联电喷雾电离质谱（ESIMS(n)）分析，结果表明两个lex2B突变菌株仅表达来自HepI的β - d - Glcp延伸。这提供了强有力的证据，表明Lex2B在这些菌株中作为一种半乳糖基转移酶，将β - d - Galp添加到GlcI的O - 4位，表明lex2B序列中的等位基因多态性指导了该基因产物的替代功能。
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