Structural Features Affecting Trafficking, Processing, and Secretion of Trypanosoma cruzi Mucins
Structural Features Affecting Trafficking, Processing, and Secretion of Trypanosoma cruzi Mucins
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DOI：
10.1074/jbc.m112.354696
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发表时间：
2012-07-27
影响因子：
4.8
通讯作者：
Buscaglia, Carlos A.
中科院分区：
文献类型：
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作者：
Canepa, Gaspar E.;Mesias, Andrea C.;Buscaglia, Carlos A.
克氏锥虫被粘蛋白型分子的致密外壳包裹，所述粘蛋白型分子由称为TcSMUG和TcMUC的复杂基因家族编码，所述基因家族分别在寄生虫的昆虫和哺乳动物居住形式中表达。在这里，我们剖析了不同的翻译后修饰对这些糖缀合物的运输的贡献。在体内跟踪和表征的标记的变体表达的转染epimastigotes表明，虽然N-末端信号肽是负责靶向TcSMUG产品的内质网（ER），糖基磷脂酰肌醇（GPI）-锚可能作为一个向前运输信号，为他们的及时进展沿着分泌途径。GPI阴性变体在ER中积累，只有一小部分最终作为无锚定产物释放到培养基中。分泌的产品，但不是ER积累的，显示成熟粘蛋白型分子的几个诊断特征，包括广泛的O型糖基化，Galf为基础的单克隆抗体识别的表位，和末端Galp残基，成为容易唾液酸化后，除了寄生虫转唾液酸酶。N-糖基化位点的加工对于整个TcSMUG粘蛋白型成熟和分泌是必需的。尽管经历了不同的O-糖基化加工，TcMUC报告基因产生了非常相似的结果，从而表明（i）粘蛋白家族之间的分子运输信号在结构上和功能上是保守的，以及（ii）TcMUC和TcSMUG产物被阶段特异性糖基转移酶的不同库识别和加工。因此，利用同源表达系统的保真度，我们已经确定了T.克氏粘蛋白，参与寄生虫保护和毒力的关键分子。
Trypanosoma cruzi is wrapped by a dense coat of mucin-type molecules encoded by complex gene families termed TcSMUG and TcMUC, which are expressed in the insect-and mammal-dwelling forms of the parasite, respectively. Here, we dissect the contribution of distinct post-translational modifications on the trafficking of these glycoconjugates. In vivo tracing and characterization of tagged-variants expressed by transfected epimastigotes indicate that although the N-terminal signal peptide is responsible for targeting TcSMUG products to the endoplasmic reticulum (ER), the glycosyl phosphatidylinositol (GPI)-anchor likely functions as a forward transport signal for their timely progression along the secretory pathway. GPI-minus variants accumulate in the ER, with only a minor fraction being ultimately released to the medium as anchorless products. Secreted products, but not ER-accumulated ones, display several diagnostic features of mature mucin-type molecules including extensive O-type glycosylation, Galf-based epitopes recognized by monoclonal antibodies, and terminal Galp residues that become readily sialylated upon addition of parasite trans-sialidases. Processing of N-glycosylation site(s) is dispensable for the overall TcSMUG mucin-type maturation and secretion. Despite undergoing different O-glycosylation elaboration, TcMUC reporters yielded quite similar results, thus indicating that (i) molecular trafficking signals are structurally and functionally conserved between mucin families, and (ii) TcMUC and TcSMUG products are recognized and processed by a distinct repertoire of stage-specific glycosyltransferases. Thus, using the fidelity of a homologous expression system, we have defined some biosynthetic aspects of T. cruzi mucins, key molecules involved in parasite protection and virulence.