Amyloid-like Interactions in Fungal Aggregation

描述（由申请人提供）：真菌感染是发病的主要原因， 免疫功能低下患者的死亡率，白色念珠菌是主要的致病真菌。粘附和定殖是发病机制中至关重要的第一步，ALS基因家族的细胞壁粘附素，包括Als 1 p和AIs 5 p，介导与细胞外基质的粘附和真菌聚集成小菌落。我们的长期目标是了解真菌粘附素在细胞相互作用中的机制和作用。我们目前的目标是描绘AIs 5 p的分子特性和活性。AIs 5 p与不同的肽配体结合，并介导底物粘附和酿酒酵母细胞与表面上展示的蛋白质的细胞聚集。我们的工作假设是，AIs 5 p与不同的肽配体的结合介导粘附，并触发从熔融球样状态到以淀粉样蛋白样质量缔合为特征的状态的自传播构象转变。这种构象转变介导细胞缔合以形成宏观聚集体。四个具体的目标，根据初步结果，将确定这两个活动是否可以定位到特定的结构域的蛋白质，或者，如何相互作用的结构域介导的粘附和聚集。这些目的是对特定假设的检验：1）粘附是由AIs 5 p的球状N-末端结构域与特定肽配体的结合引起的; 2）粘附是由AIs 5 p的球状N-末端结构域与特定肽配体的结合引起的。 Als 1 p和Als 5 p的配体特异性的差异是由于球状N-末端区域序列的差异; 3）Als 5 p的富含Th的结构域介导同型缔合，以及重复数量的影响的测试;和4）粘附导致Als 5 p中的自传播全局构象变化，导致表达粘附素的细胞聚集。这项工作将是创新的，因为淀粉样蛋白样状态的构象转变的模型还没有被应用到细胞粘附。此外，该模型涉及一种广泛分布的序列类型（Thr丰富），以前没有研究过。这项工作的基本原理是，它将阐明一种新的细胞粘附策略，在一个共同的和严重的病原体。结果将是普遍的，因为AI同源物存在于其他病原真菌中，并且在其他病原体（包括葡萄球菌、结核分枝杆菌和疟原虫）的细胞表面蛋白中发现了类似的富含Thr的序列。

DESCRIPTION (provided by applicant): Fungal infections are a major cause of morbidity and mortality in immunocompromised patients, and Candida albicans is the major causative fungal agent. Adhesion and colonization are crucial first steps in pathogenesis, and cell wall adhesins of the ALS gene family, including Als1p and AIs5p, mediate both adhesion to extracellular matrix and aggregation of the fungus into mini-colonies. Our long term goal is to understand the mechanisms and role of fungal adhesins in cellular interactions. Our current objective is to delineate the molecular properties and activities of AIs5p. AIs5p binds to diverse peptide ligands and mediates both substrate adhesion and cellular aggregation of Saccharomyces cerevisiae cells with the protein displayed on the surface. Our working hypothesis is that binding of AIs5p to diverse peptide ligands mediates adhesion and triggers a self-propagating conformational shift from a molten-globule-like state to a state characterized by amyloid-like mass association. This conformational shift mediates cell association to form macroscopic aggregates. Four specific aims, based on preliminary results, will determine whether these two activities can be localized to specific domains of the protein, or alternatively, how the domains interact to mediate adhesion and aggregation. These aims are tests of specific hypotheses: 1) that adhesion results from binding of the globular N-terminal domain of AIs5p to specific peptide ligands; 2) that the differences in ligand specificities of Als1p and AIs5p are due to differences in sequence of the globular N-terminal regions; 3) that the Thr-rich domains of AIs5p mediate homotypic association, and a test of the effect of the number of repeats; and 4) that adhesion leads to self-propagating global conformational change in AIs5p, resulting in aggregation of cells that express the adhesin. This work will be innovative in that a model of conformational shift to an amyloid-like state has not been applied to cell adhesion. Furthermore, this model involves a widespread type of sequence (Thr-rich) that has not been studied before. The rationale for this work is that it will elucidate a novel cell-adhesion strategy in a common and serious pathogen. The results will be general in that AIs homologs are present in other pathogenic fungi, and similar Thr-rich sequences are found in cell surface proteins in other pathogens including Staphylococcus, Mycobacterium tuberculosis, and Plasmodium.