Host glycosyltransferases in the glycosylation of Toxoplasma proteins

描述（由申请方提供）：原生动物寄生虫弓形虫是一种重要的感染，可导致HIV-AIDS和其他免疫抑制疾病患者发生危及生命的疾病。尽管激活了强有力的免疫应答，包括感染个体中的高抗体滴度，但未实现无菌治愈。相反，寄生虫分化为代谢相对静止的组织包囊形式。在肌肉和CNS内建立的组织囊肿的特征在于具有高度糖基化的囊壁和基质。一个给定的囊肿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鉴定了脑源性和组织培养诱导的囊肿的组织囊肿壁和基质中含有唾液酸的聚糖的存在。鉴于在寄生虫基因组中发现的唾液酸合成、活化和转移的任何机制的缺乏，这一发现是显著的。这一发现的含义是， 宿主活动可能是组织囊肿相关聚糖唾液酸化的原因。在本研究中，我们通过使用在唾液酸化途径的不同步骤中具有缺陷的已建立的宿主细胞突变体来证实宿主细胞的贡献来探索这种根本假设。此外，还将使用siRNA敲除来靶向特定的宿主活性，以建立所涉及的唾液酸转移酶的类别。最后，我们将开发分裂GFP/Luc为基础的系统，以解决是否融合的寄生虫空泡膜和相关的ER，以及高尔基体相关囊泡的重定向参与从宿主细胞的囊肿修饰糖基化酶的交付。我们认为，通过劫持宿主自身的糖基化机制，寄生虫可以通过有效地用“自身”糖“包裹潜在的抗原决定簇，使它们在功能上不可见，从而避免被免疫系统检测到。

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.