Schwingel Johanna M, St Michael Frank, Cox Andrew D, Masoud Hussein, Richards James C, Campagnari Anthony A
Department of Microbiology and Immunology, State University of New York at Buffalo, Buffalo, NY 14214, USA.
Glycobiology. 2008 Jun;18(6):447-55. doi: 10.1093/glycob/cwn021. Epub 2008 Mar 12.
Moraxella catarrhalis express three predominant forms of lipooligosaccharide (LOS) molecules on the bacterial surface. These major glycolipids contain specific carbohydrate epitopes that distinguish each glycoform into serotype A, B, or C LOS. All three serotypes, however, share a common glucose containing inner-core structure, consisting of an alpha-glucose attached to 2-keto-3-deoxyoctulosonic acid (KDO), which is unique among Gram-negative bacteria. Many of the LOS glycosyltransferase genes (lgt) responsible for assembly of the extended M. catarrhalis LOS structure have been identified. In this report, we now describe the identification and characterization of Lgt6, a unique glycosyltransferase that is responsible for the addition of the first glucose to the inner core thus initiating the assembly of full length LOS. Isogenic mutants defective in the expression of lgt6 were constructed in all three M. catarrhalis LOS serotypes and the resulting LOS glycoforms consisted of KDO(2)-lipid A-OH as analyzed by urea sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry. In addition, the expression of lgt6 in trans in a heptose-deficient Neisseria meningitidis NMB gmhX mutant resulted in the addition of a hexose to the LOS of this strain. These studies demonstrate that Lgt6 functions as an alpha-(1-5)-glucosyltransferase in M. catarrhalis adding the primary glucose to the KDO(2)-lipid A-OH in LOS biosynthesis. The function of Lgt6 is required for the completion of both the major and minor oligosaccharide chains in M. catarrhalis.
卡他莫拉菌在细菌表面表达三种主要形式的脂寡糖（LOS）分子。这些主要的糖脂含有特定的碳水化合物表位，可将每种糖型区分为A、B或C型LOS血清型。然而，所有这三种血清型都共享一个含葡萄糖的共同内核结构，该结构由连接到2-酮-3-脱氧辛糖酸（KDO）上的α-葡萄糖组成，这在革兰氏阴性菌中是独特的。许多负责卡他莫拉菌LOS扩展结构组装的LOS糖基转移酶基因（lgt）已被鉴定。在本报告中，我们现在描述了Lgt6的鉴定和特性，Lgt6是一种独特的糖基转移酶，负责将第一个葡萄糖添加到内核，从而启动全长LOS的组装。在所有三种卡他莫拉菌LOS血清型中构建了lgt6表达缺陷的同基因突变体，通过尿素十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）和质谱分析，所得的LOS糖型由KDO(2)-脂多糖A-OH组成。此外，在七糖缺陷的脑膜炎奈瑟菌NMB gmhX突变体中反式表达lgt6导致该菌株的LOS添加了一个己糖。这些研究表明，Lgt6在卡他莫拉菌中作为α-(1-5)-葡萄糖基转移酶发挥作用，在LOS生物合成中向KDO(2)-脂多糖A-OH添加初级葡萄糖。Lgt6的功能是卡他莫拉菌中主要和次要寡糖链完成所必需的。
