National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080-8555, Japan.
Infect Immun. 2010 May;78(5):2138-45. doi: 10.1128/IAI.01102-09. Epub 2010 Feb 16.
Proteins with tandem repeat (TR) domains have been found in various protozoan parasites, and they are often targets of B-cell responses. Through systematic analyses of whole proteomes, we recently demonstrated that two trypanosomatid parasites, Leishmania infantum and Trypanosoma cruzi, are rich in antigenic proteins with large TR domains. However, the reason that these proteins are antigenic was unclear. Here, by performing molecular, immunological, and bioinformatic characterizations of Leishmania TR proteins, we found two possible factors affecting the antigenicity of these proteins; one factor is their fundamental composition as TR proteins, and the other is regulation of their expression by parasites. Enzyme-linked immunosorbent assays (ELISAs) using recombinant proteins revealed that the copy number of the repeat affects the affinity of binding between antigens and antibodies, as expected based on thermodynamic binding kinetics. Other than containing TR domains, the TR proteins do not share characteristics, such as sequence similarity or biased cellular location predicted by the presence of a signal sequence(s) and/or a transmembrane domain(s). However, the TR proteome contained a higher percentage of proteins upregulated in amastigotes than the whole proteome, and upregulated expression of a TR protein seemed to affect its antigenicity. These results indicate that Leishmania parasites actively utilize the TR protein family for parasitism in mammalian hosts.
具有串联重复 (TR) 结构域的蛋白质已在各种原生动物寄生虫中被发现，它们通常是 B 细胞反应的靶标。通过对整个蛋白质组的系统分析，我们最近证明两种锥虫寄生虫，即婴儿利什曼原虫和克氏锥虫，富含具有大 TR 结构域的抗原性蛋白。然而，这些蛋白质具有抗原性的原因尚不清楚。在这里，通过对婴儿利什曼原虫 TR 蛋白进行分子、免疫学和生物信息学的特征分析，我们发现了两个可能影响这些蛋白抗原性的因素；一个因素是它们作为 TR 蛋白的基本组成，另一个是寄生虫对其表达的调控。使用重组蛋白进行酶联免疫吸附测定 (ELISA) 显示，重复的拷贝数影响抗原和抗体之间结合的亲和力，这与热力学结合动力学的预期相符。除了含有 TR 结构域外，TR 蛋白不具有序列相似性或信号序列 (s) 和/或跨膜结构域 (s) 存在所预测的偏向细胞位置等特征。然而，TR 蛋白质组中上调表达的蛋白百分比高于整个蛋白质组，并且 TR 蛋白的上调表达似乎影响其抗原性。这些结果表明，利什曼原虫寄生虫积极利用 TR 蛋白家族在哺乳动物宿主中寄生。
