首頁> 外文期刊>Biochimica et Biophysica Acta. Molecular and cell biology of Lipids >Altered lipid A structures and polymyxin hypersensitivity of Rhizobium etli mutants lacking the LpxE and LpxF phosphatases.
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Altered lipid A structures and polymyxin hypersensitivity of Rhizobium etli mutants lacking the LpxE and LpxF phosphatases.

機(jī)譯：缺少LpxE和LpxF磷酸酶的根瘤菌等突變體的脂質(zhì)A結(jié)構(gòu)改變和多粘菌素超敏性。

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The lipid A of Rhizobium etli, a nitrogen-fixing plant endosymbiont, displays significant structural differences when compared to that of Escherichia coli. An especially striking feature of R. etli lipid A is that it lacks both the 1- and 4'-phosphate groups. The 4'-phosphate moiety of the distal glucosamine unit is replaced with a galacturonic acid residue. The dephosphorylated proximal unit is present as a mixture of the glucosamine hemiacetal and an oxidized 2-aminogluconate derivative. Distinct lipid A phosphatases directed to the 1 or the 4'-positions have been identified previously in extracts of R. etli and Rhizobium leguminosarum. The corresponding structural genes, lpxE and lpxF, respectively, have also been identified. Here, we describe the isolation and characterization of R. etli deletion mutants in each of these phosphatase genes and the construction of a double phosphatase mutant. Mass spectrometry confirmed that the mutant strains completely lacked the wild-type lipid A species and accumulated the expected phosphate-containing derivatives. Moreover, radiochemical analysis revealed that phosphatase activity was absent in membranes prepared from the mutants. Our results indicate that LpxE and LpxF are solely responsible for selectively dephosphorylating the lipid A molecules of R. etli. All the mutant strains showed an increased sensitivity to polymyxin relative to the wild-type. However, despite the presence of altered lipid A species containing one or both phosphate groups, all the phosphatase mutants formed nitrogen-fixing nodules on Phaseolus vulgaris. Therefore, the dephosphorylation of lipid A molecules in R. etli is not required for nodulation but may instead play a role in protecting the bacteria from cationic antimicrobial peptides or other immune responses of plants.
機(jī)譯：與大腸桿菌相比，固氮植物內(nèi)共生體的根瘤菌脂質(zhì)A具有明顯的結(jié)構(gòu)差異。 R. etli脂質(zhì)A的一個特別醒目的特征是它同時缺少1和4'-磷酸基團(tuán)。遠(yuǎn)端葡糖胺單元的4'-磷酸部分被半乳糖醛酸殘基取代。脫磷酸的近端單元以氨基葡萄糖半縮醛和氧化的2-氨基葡萄糖酸酯衍生物的混合物形式存在。先前已經(jīng)在R. etli和豆科根瘤菌的提取物中鑒定了針對1或4'-位的不同脂質(zhì)A磷酸酶。還分別鑒定了相應(yīng)的結(jié)構(gòu)基因lpxE和lpxF。在這里，我們描述了在這些磷酸酶基因的每一個中R. etli缺失突變體的分離和特征以及雙磷酸酶突變體的構(gòu)建。質(zhì)譜證實突變菌株完全缺乏野生型脂質(zhì)A種類，并積累了預(yù)期的含磷酸鹽的衍生物。此外，放射化學(xué)分析表明由突變體制備的膜中不存在磷酸酶活性。我們的結(jié)果表明，LpxE和LpxF僅負(fù)責(zé)選擇性地使R. etli的脂質(zhì)A分子脫磷酸。相對于野生型，所有突變菌株均顯示出對多粘菌素的敏感性增加。然而，盡管存在含有一個或兩個磷酸基團(tuán)的脂質(zhì)A物種的改變，但所有磷酸酶突變體均在菜豆上形成了固氮根瘤。因此，結(jié)瘤不需要脂質(zhì)中的脂質(zhì)A分子去磷酸化，而是可以起到保護(hù)細(xì)菌免受陽離子抗微生物肽或植物其他免疫反應(yīng)的作用。

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