Sernee M Fleur, Ralton Julie E, Dinev Zoran, Khairallah George N, O'Hair Richard A, Williams Spencer J, McConville Malcolm J
Department of Biochemistry and Molecular Biology, University of Melbourne, 30 Flemington Road, Parkville, Victoria 3010, Australia.
Proc Natl Acad Sci U S A. 2006 Jun 20;103(25):9458-63. doi: 10.1073/pnas.0603539103. Epub 2006 Jun 9.
Infective stages of the protozoan parasite Leishmania spp. accumulate a class of beta-1,2-mannan oligosaccharides as their major carbohydrate reserve material. Here, we describe the biosynthesis of Leishmania mannan. Mannan precursors were identified by metabolic labeling of Leishmania mexicana promastigotes with [(3)H]mannose. Label was initially incorporated into a phosphomannose primer and short phosphorylated beta-1,2-mannan oligomers that were two to five residues long. Analysis of the mannan primer by Fourier transform ion-cyclotron resonance MS and various enzymatic and chemical treatments and comparison with authentic mannose (Man) phosphates indicated the presence of Man-alpha-1,4-cyclic phosphate. This primer was synthesized from Man-6-phosphate by means of Man-1-phosphate in a cell-free system. Short mannan chains containing the primer were subsequently dephosphorylated and then further elongated by GDP-Man-dependent transferases in vivo and in the cell-free system. The synthesis of this glycan primer likely constitutes a key regulatory step in mannan biosynthesis and is a potential target for antileishmanial drugs.
原生动物寄生虫利什曼原虫属的感染阶段积累了一类β-1,2-甘露聚糖寡糖作为其主要的碳水化合物储备物质。在此，我们描述了利什曼原虫甘露聚糖的生物合成。通过用[³H]甘露糖对墨西哥利什曼原虫前鞭毛体进行代谢标记来鉴定甘露聚糖前体。标记最初掺入到磷酸甘露糖引物和长度为两到五个残基的短磷酸化β-1,2-甘露聚糖寡聚物中。通过傅里叶变换离子回旋共振质谱、各种酶促和化学处理对甘露聚糖引物进行分析，并与真实的甘露糖（Man）磷酸盐进行比较，结果表明存在Man-α-1,4-环磷酸酯。该引物在无细胞系统中由6-磷酸甘露糖通过1-磷酸甘露糖合成。随后，含有该引物的短甘露聚糖链被去磷酸化，然后在体内和无细胞系统中由依赖GDP-Man的转移酶进一步延长。这种聚糖引物的合成可能构成甘露聚糖生物合成中的关键调节步骤，并且是抗利什曼原虫药物的潜在靶点。
