Host glycosyltransferases in the glycosylation of Toxoplasma proteins

描述(申请人提供)：原生动物寄生虫弓形虫是一种重要的感染，在艾滋病毒-艾滋病和其他免疫抑制情况下会导致危及生命的疾病。尽管在感染个体中激活了强大的免疫反应，包括高抗体效价，但没有实现无菌治愈。相反，这种寄生虫分化成一种相对代谢静止的组织囊状结构。建立在肌肉和中枢神经系统内的组织囊肿的特点是囊壁和基质高度糖基化。一个给定的包囊可能含有数百个单独的寄生虫。我们使用凝集素反应性的研究已经证实，在脑源性和组织培养诱导的囊壁和基质中都存在含有唾液酸的多糖。考虑到寄生虫基因组中没有任何合成、激活和转移唾液酸的机制，这一发现是值得注意的。这一发现的含义是 宿主的活动可能是导致组织胞囊相关的糖链裂解的原因。在这项研究中，我们通过在唾液酸化途径的不同步骤中存在缺陷的已建立的宿主细胞突变体来证实宿主细胞的贡献，从而探索这一激进假设。此外，还将使用siRNA敲除来针对特定的宿主活动，以确定所涉及的唾液酸基转移酶的类别。最后，我们将开发基于分离式GFP/Luc的系统，以解决寄生虫液泡膜和相关ER的融合以及高尔基体相关囊泡的重定向是否参与从宿主细胞运送孢子修饰的糖基质酶。我们认为，通过劫持宿主自身的糖基化机制，寄生虫可能会通过有效地将潜在的抗原决定簇与“自身”糖包裹在一起，使它们在功能上不可见，从而避免被免疫系统发现。

DESCRIPTION (provided by applicant): The protozoan parasite Toxoplasma gondii is an important infection causing life threatening disease in patients with HIV-AIDs and other immune suppressive conditions. Despite the activation of a robust immune response including high antibody titers in infected individuals, sterile cure is not achieved. Rather the parasite differentiates into a relatively metabolically quiescent tissue cyst form. Tissue cysts which establish within muscle and the CNS, are characterized by having a highly glycosylated cyst wall and matrix. A given cyst may contain several hundred individual parasites. Our studies using lectin reactivity have identified the presence of sialic acid containing glycans in the tissu cyst wall and matrix of both brain derived and tissue culture induced cysts. This finding is remarkable in light of the absence of any of the machinery for the synthesis, activation and transfer of sialic acid being found in the parasite genome. The implication of this finding is that host activities may be responsible for the sialylation of the tissue cyst associated glycans. In ths study we explore this radical hypothesis by using established host cell mutants with defects in distinct steps of the sialylation pathway to confirm the contribution of the host cell. In addition specific host activities will also be targeted using siRNA knockdowns to establish the classes of sialyltransferases involved. Finally we will develop as split GFP/Luc based system to address whether fusion of the parasitophorous vacuole membrane and the associated ER as well as the redirection of Golgi associated vesicles is involved in the delivery of cyst modifying glycosylatin enzymes from the host cell. We believe that by hijacking the host's own glycosylation machinery, the parasite may avoid detection by the immune system by effectively "sugar coating" potentially antigenic determinants with "self" sugars rendering them functionally invisible.