McConville M J, Homans S W
Department of Biochemistry, University of Dundee, United Kingdom.
J Biol Chem. 1992 Mar 25;267(9):5855-61.
The major macromolecule on the surface of the protozoan parasite, Leishmania major, is a complex lipophosphoglycan (LPG), which is anchored to the plasma membrane by an inositol-containing phospholipid. A defect in LPG biosynthesis is thought to be responsible for the avirulence of the L. major strain LRC L119 in mice. In order to identify the nature of this defect we have characterized two truncated forms of LPG, which are accumulated in this strain, by one- and two-dimensional 500-MHz 1H NMR spectroscopy, two-dimensional heteronuclear 1H-31P NMR spectroscopy, methylation analysis, and exoglycosidase digestions. The structures of these glycoinositolphospholipids, termed GIPL-4 and -6, are as follows: [formula: see text] The glycan moieties of GIPL-4 and -6 are identical to the anchor region of LPG, which is also substituted with a Glc-1-PO4 residue in approximately 60% of the structures. However, instead of being capped with chains of phosphorylated oligosaccharide repeat units, both glycan moieties terminate in Man alpha 1-PO4, suggesting that the defect in LPG biosynthesis is in the transfer of galactose to this residue to form the disaccharide backbone of the first repeat unit. These results indicate that the phosphoglycan moiety of LPG is essential for intracellular survival of the parasite and have implications for LPG biosynthesis.
原生动物寄生虫硕大利什曼原虫表面的主要大分子是一种复杂的脂磷壁酸（LPG），它通过含肌醇的磷脂锚定在质膜上。LPG生物合成缺陷被认为是硕大利什曼原虫菌株LRC L119在小鼠中无毒力的原因。为了确定这种缺陷的本质，我们通过一维和二维500兆赫1H核磁共振光谱、二维异核1H-31P核磁共振光谱、甲基化分析和外切糖苷酶消化，对在该菌株中积累的两种截短形式的LPG进行了表征。这些糖基肌醇磷脂（称为GIPL-4和-6）的结构如下：[化学式：见正文]GIPL-4和-6的聚糖部分与LPG的锚定区域相同，在大约60%的结构中也被一个Glc-1-PO4残基取代。然而，两个聚糖部分都不是以磷酸化寡糖重复单元链封端，而是以Manα1-PO4终止，这表明LPG生物合成的缺陷在于半乳糖向该残基的转移，以形成第一个重复单元的二糖主链。这些结果表明LPG的磷聚糖部分对寄生虫的细胞内存活至关重要，并对LPG生物合成具有启示意义。
