McConville M J, Blackwell J M
Department of Biochemistry, University of Dundee, United Kingdom.
J Biol Chem. 1991 Aug 15;266(23):15170-9.
In addition to utilizing glycosylated phosphatidylinositols (GPIs) as anchors for surface proteins, protozoan parasites of the genus Leishmania synthesize two novel classes of GPI: the polydisperse lipophosphoglycans (LPGs) and a family of low molecular weight glycoinositol phospholipids (GIPLs). We now show that LPG is expressed in high copy number (6 x 10(6) molecules/cell) in the promastigote (insect) stage of L. donovani but not in the amastigote stage, which infects mammalian macrophages. Detection of these molecules was by gas chromatography-mass spectrometric analyses and by a sensitive radiolabeling procedure. In contrast, a novel family of GIPLs was present in high copy number (approximately 10(7) molecules/cell) in both promastigote and amastigote stages of L. donovani. These glycolipids were purified and analyzed by gas chromatography-mass spectrometry, methylation analysis, and by chemical and enzymatic sequencing after deamination and NaB3H4 reduction. Promastigotes contained three major GIPLs species with the following generalized structure [formula: see text] where R = H for isoM2, Man alpha 1- for isoM3 or Man alpha 1-2Man alpha 1- for isoM4. Amastigotes contained two major GIPL species that lacked the alpha 1-3-linked mannose branch and had the linear structures Man alpha 1-6Man alpha 1-4GlcN (M2) and Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcN (M3) linked to alkylacyl-PI. The 1-O-alkyl-2-acyl-PI moieties of all these species contained predominantly C18:0 alkyl chains and C16:0 or C18:0 fatty acids. Amastigotes contained, in addition, a GalNAc beta 1-3 terminating glycosphingolipid with homology to the mammalian para Forssman glycolipid. This glycolipid appeared to be a constituent of the parasite membrane but was not metabolically labeled with [3H]glucose, suggesting that it was acquired from host cells. These results suggest that LPG may not be required for amastigote survival in the mammalian host and that the GIPLs are likely to be major components on the surface membrane in both stages.
除了利用糖基化磷脂酰肌醇（GPI）作为表面蛋白的锚定物外，利什曼原虫属的原生动物寄生虫还合成了两类新型GPI：多分散性脂磷壁酸（LPG）和一类低分子量糖肌醇磷脂（GIPL）。我们现在发现，LPG在杜氏利什曼原虫的前鞭毛体（昆虫）阶段以高拷贝数（6×10⁶个分子/细胞）表达，但在感染哺乳动物巨噬细胞的无鞭毛体阶段不表达。这些分子通过气相色谱 - 质谱分析和灵敏的放射性标记程序进行检测。相比之下，一类新型的GIPL在杜氏利什曼原虫的前鞭毛体和无鞭毛体阶段均以高拷贝数（约10⁷个分子/细胞）存在。这些糖脂经纯化后通过气相色谱 - 质谱分析、甲基化分析以及脱氨和NaB₃H₄还原后的化学和酶促测序进行分析。前鞭毛体含有三种主要的GIPL种类，具有以下通用结构[公式：见原文]，其中对于异M2，R = H；对于异M3，R = Manα1 - ；对于异M4，R = Manα1 - 2Manα1 - 。无鞭毛体含有两种主要的GIPL种类，它们缺乏α1 - 3连接的甘露糖分支，具有与烷基酰基 - PI相连的线性结构Manα1 - 6Manα1 - 4GlcN（M2）和Manα1 - 2Manα1 - 6Manα1 - 4GlcN（M3）。所有这些种类的1 - O - 烷基 - 2 - 酰基 - PI部分主要含有C18:0烷基链和C16:0或C18:0脂肪酸。此外，无鞭毛体含有一种与哺乳动物副福斯曼糖脂具有同源性的GalNAcβ1 - 3末端糖鞘脂。这种糖脂似乎是寄生虫膜的一个组成部分，但未被[³H]葡萄糖代谢标记，这表明它是从宿主细胞获得的。这些结果表明，LPG可能不是无鞭毛体在哺乳动物宿主中存活所必需的，并且GIPL可能是两个阶段表面膜的主要成分。
