Functional analysis of the O antigen glucosylation gene cluster of Shigella flexneri bacteriophage SfX
Functional analysis of the O antigen glucosylation gene cluster of Shigella flexneri bacteriophage SfX
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DOI：
10.1099/13500872-145-5-1263
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发表时间：
1999-05-01
期刊：
影响因子：
--
通讯作者：
Verma, NK
中科院分区：
文献类型：
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作者：
Guan, S;Bastin, DA;Verma, NK
以往的研究表明，福氏志贺氏菌噬菌体X(SFX)编码一种葡萄糖转移酶(GtrX，前身为GtR)，参与O抗原修饰(血清Y型为X型)。然而，仅GtrX本身只能调解部分转换。最近，在另外两个福氏志贺氏菌噬菌体(即SFV和SfII)基因组的附着部位附近发现了一个三基因簇。这个基因簇被认为是导致全O抗原转换的原因。有报道称，除gtrX基因外，SFX基因中的另外两个基因也参与O抗原的修饰过程。该簇中的第一个基因(GtrA)编码一个小的高度疏水的蛋白，它似乎参与了脂质连接的葡萄糖跨细胞膜的转运。该簇中的第二个基因(GtrB)编码一种酶，催化葡萄糖残基从UDP-葡萄糖转移到脂质载体上。第三个基因(GtrX)编码一种噬菌体特异性的葡萄糖转移酶，它主要负责最后一步，即将葡萄糖分子连接到O抗原重复单元的正确糖基上。提出了细菌O抗原糖基化的三步模型。
Previous studies have shown that Shigella flexneri bacteriophage X (SfX) encodes a glucosyltransferase (GtrX, formerly Gtr), which is involved in O antigen modification (serotype Y to serotype X). However, GtrX alone can only mediate a partial conversion. More recently, a three-gene cluster has been identified next to the attachment site in the genome of two other S. flexneri bacteriophages (i.e. SfV and SfII). This gene cluster was postulated to be responsible for a full O antigen conversion. Here it is reported that besides the gtrX gene, the other two genes in the gtr focus of SfX were also involved in the O antigen modification process. The first gene in the cluster (gtrA) encodes a small highly hydrophobic protein which appears to be involved in the translocation of lipid-linked glucose across the cytoplasmic membrane. The second gene in the cluster (gtrB) encodes an enzyme catalysing the transfer of the glucose residue from UDP-glucose to a lipid carrier. The third gene (gtrX) encodes a bacteriophage-specific glucosyltransferase which is largely responsible for the final step, i.e. attaching the glucosyl molecules onto the correct sugar residue of the O antigen repeating unit. A three-step model for the glucosylation of bacterial O antigen has been proposed.