Cryptococcus neoformans is an important human, fungal pathogen that sheds polysaccharide (exo-PS) into host tissues. While shed exo-PS mediates numerous untoward effects (including promoting increased intracranial pressure), little is known about the regulation of this phenomenon. Since downregulation of the Allergen 1 (ALL1) gene is associated with high ICP, we investigated the relationship between ALL1 expression and exo-PS structure using a variety of biophysical techniques. The Δall1 mutants of two serotypes produced a shorter exo-PS with less branching and structural complexity than the parental strains. Consistent with lower branching, these exo-PSs manifested higher intrinsic viscosity than the parental strains. The Δall1 mutant strains manifested differences in epitope expression and significant resistance to phagocytosis. Exo-PS of Δall1 mutant exhibited anti-phagocytic properties. Comparative transcriptome analysis of mutant and parental strain under iron-deprived conditions indicated a role of ALL1 in iron homeostasis, characterized by differential regulation of genes that mediate iron reduction and transport. Together, our results demonstrate a role of ALL1 in regulating conformational aspects of PS structure and iron homeostasis. These findings provide a mechanism to explain how changes in ALL1 expression influence virulence of switch variants and suggest that structural changes and polymer length are epigenetically regulated.

译文

新型隐球菌是一种重要的人类真菌病原体,可将多糖 (exo-PS) 分解到宿主组织中。虽然shed exo-PS介导了许多不良影响 (包括促进颅内压升高),但对这种现象的调节知之甚少。由于过敏原1 (ALL1) 基因的下调与高ICP有关,因此我们使用多种生物物理技术研究了ALL1表达与exo-PS结构之间的关系。与亲本菌株相比,两种血清型的 Δall1突变体产生的exo-ps较短,分支和结构复杂性较小。与较低的支化一致,这些exo-PSs表现出比亲本菌株更高的特性粘度。Δall1突变菌株表现出表位表达的差异和对吞噬作用的显着抗性。Δall1突变体的Exo-PS具有抗吞噬特性。在缺铁条件下对突变体和亲本菌株的比较转录组分析表明,ALL1在铁稳态中的作用,其特征是介导铁还原和转运的基因的差异调节。总之,我们的结果证明了ALL1在调节PS结构和铁稳态的构象方面的作用。这些发现提供了一种机制来解释ALL1表达的变化如何影响开关变体的毒力,并表明结构变化和聚合物长度受到表观遗传调控。

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