Parallel β-helix proteins required for accurate capsule polysaccharide synthesis and virulence in the yeast Cryptococcus neoformans
Parallel β-helix proteins required for accurate capsule polysaccharide synthesis and virulence in the yeast Cryptococcus neoformans
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DOI：
10.1128/ec.00398-06
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发表时间：
2007-04-01
期刊：
影响因子：
--
通讯作者：
Madhani, Hiten D.
中科院分区：
文献类型：
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作者：
Liu, Oliver W.;Kelly, Mark J. S.;Madhani, Hiten D.
机会性真菌病原体新型隐球菌的主要荚膜多糖由 α-1,3 连接的甘露糖主链组成，主链上装饰有葡萄糖醛酸基和木糖基侧基的重复图案。这种结构对于毒力至关重要，但人们对这种被称为葡萄糖醛酸木甘露聚糖 (GXM) 的聚合物如何准确合成和组装知之甚少。我们在编码预测的平行 P 螺旋重复蛋白的两个基因中产生了缺失，我们将其命名为 PBX1 和 PBX2。任一基因的缺失都会导致干集落形态、细胞成块和荚膜完整性降低。来自突变体的纯化 GXM 的二维核磁共振波谱表明，存在野生型 GXM 结构和新颖的异常连接。碳水化合物组成和连接分析确定这些异常结构与野生型荚膜多糖中未发现的末端葡萄糖残基的掺入相关。我们得出结论，Pbx1 和 Pbx2 对于 GXM 合成的保真度是必需的，并且可能参与编辑错误添加的葡萄糖残基。 PBX1 和 PBX2 敲除突变体在隐球菌病小鼠吸入模型中表现出严重减弱的毒力。与无荚膜菌株不同，这些突变菌株会诱发隐球菌病的延迟症状，尽管受感染的动物最终控制住了感染并康复了。
The principal capsular polysaccharide of the opportunistic fungal pathogen Cryptococcus neoformans consists of an alpha-1,3-linked mannose backbone decorated with a repeating pattern of glucuronyl and xylosyl side groups. This structure is critical for virulence, yet little is known about how the polymer, called glucuronoxylomannan (GXM), is faithfully synthesized and assembled. We have generated deletions in two genes encoding predicted parallel P-helix repeat proteins, which we have designated PBX1 and PBX2. Deletion of either gene results in a dry-colony morphology, clumpy cells, and decreased capsule integrity. Two-dimensional nuclear magnetic resonance spectroscopy of purified GXM from the mutants indicated that both the wild-type GXM structure and novel, aberrant linkages were present. Carbohydrate composition and linkage analysis determined that these aberrant structures are correlated with the incorporation of terminal glucose residues that are not found in wild-type capsule polysaccharide. We conclude that Pbx1 and Pbx2 are required for the fidelity of GXM synthesis and may be involved in editing incorrectly added glucose residues. PBX1 and PBX2 knockout mutants showed severely attenuated virulence in a murine inhalation model of cryptococcosis. Unlike acapsullar strains, these mutant strains induced delayed symptoms of cryptococcosis, though the infected animals eventually contained the infection and recovered.