Host glycosyltransferases in the glycosylation of Toxoplasma proteins

描述（由申请人提供）：弓形虫是一种重要的原虫寄生虫，在HIV-AIDs和其他免疫抑制疾病患者中引起危及生命的疾病。尽管激活了强大的免疫反应，包括感染个体的高抗体滴度，但无法实现无菌治愈。相反，寄生虫分化成代谢相对静止的组织囊肿形式。组织囊肿建立在肌肉和中枢神经系统内，其特征是具有高度糖基化的囊肿壁和基质。一个囊肿可能含有几百个寄生虫。我们利用凝集素反应性的研究发现，在脑源性和组织培养性囊肿的组织囊肿壁和基质中都存在含聚糖的唾液酸。这一发现是值得注意的，因为在寄生虫基因组中没有发现任何用于唾液酸合成、激活和转移的机制。这一发现的含义是

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.