Ramiscal Roybel R, Tang Swee-Seong, Korres Haralambos, Verma Naresh K
Division of Biomedical Science and Biochemistry, Research School of Biology, Australian National University, Canberra, Australia.
Mol Membr Biol. 2010 Apr;27(2-3):114-22. doi: 10.3109/09687680903552250.
Glucosyltransferases (Gtrs) and O-acetyltransferase (Oac) are integral membrane proteins embedded within the cytoplasmic membrane of Shigella flexneri. Gtrs and Oac are responsible for unidirectional host serotype conversion by altering the epitopic properties of the bacterial surface lipopolysaccharide (LPS) O-antigen. In this study, we present the membrane topology of a recently recognized Gtr, GtrIc, which is known to mediate S. flenxeri serotype switching from 1a to 1c. The GtrIc topology is shown to deviate from those typically seen in S. flexneri Gtrs. GtrIc has 11 hydrophilic loops, 10 transmembrane helices, a double intramembrane dipping loop 5, and a cytoplasmic N- and C-terminus. Along with a unique membrane topology, the identification of non-critical Gtr-conserved peptide motifs within large periplasmic loops (N-terminal D/ExD/E and C-terminal KK), which have previously been proven essential for the activity of other Gtrs, challenge current opinions of a similar mechanism for enzyme function between members of the S. flexneri Gtr family.
葡萄糖基转移酶（Gtrs）和O - 乙酰基转移酶（Oac）是嵌入弗氏志贺氏菌细胞质膜内的整合膜蛋白。Gtrs和Oac通过改变细菌表面脂多糖（LPS）O抗原的表位特性来负责单向宿主血清型转换。在本研究中，我们展示了一种最近发现的Gtr即GtrIc的膜拓扑结构，已知它介导弗氏志贺氏菌血清型从1a转换为1c。结果表明，GtrIc的拓扑结构与弗氏志贺氏菌Gtrs中常见的拓扑结构不同。GtrIc有11个亲水环、10个跨膜螺旋、一个双膜内浸入环5以及一个细胞质N端和C端。除了独特的膜拓扑结构外，在大的周质环（N端D/ExD/E和C端KK）中鉴定出非关键的Gtr保守肽基序，而这些基序先前已被证明对其他Gtrs的活性至关重要，这对弗氏志贺氏菌Gtr家族成员之间酶功能的类似机制的当前观点提出了挑战。
