Parasitology Laboratory, College of Veterinary Medicine, China Agricultural University, Beijing 100193, China.
Exp Parasitol. 2011 Jan;127(1):100-6. doi: 10.1016/j.exppara.2010.06.035. Epub 2010 Jul 3.
African trypanosomes are flagellated unicellular parasites which proliferate extracellularly in the mammalian host blood-stream and tissue spaces. They evade the hosts' antibody-mediated lyses by sequentially changing their variant surface glycoprotein (VSG). VSG tightly coats the entire parasite body, serving as a physical barrier. In Trypanosoma brucei and the closely related species Trypanosoma evansi, Trypanosoma equiperdum, each VSG polypeptide can be divided into N- and C-terminal domains, based on cysteine distribution and sequence homology. N-terminal domain, the basis of antigenic variation, is hypervariable and contains all the exposed epitopes; C-terminal domain is relatively conserved and a full set of four or eight cysteines were generally observed. We cloned two genes from two distinct variants of T. evansi, utilizing RT-PCR with VSG-specific primers. One contained a VSG type A N-terminal domain followed a C-terminal domain lacking cysteine residues. To confirm that this gene is expressed as a functional VSG, the expression and localization of the corresponding gene product were characterized using Western blotting and immunofluorescent staining of living trypanosomes. Expression analysis showed that this protein was highly expressed, variant-specific, and had a ubiquitous cellular surface localization. All these results indicated that it was expressed as a functional VSG. Our finding showed that cysteine residues in VSG C-terminal domain were not essential; the conserved C-terminal domain generally in T. brucei like VSGs would possibly evolve for regulating the VSG expression.
非洲锥虫是有鞭毛的单细胞寄生虫，在哺乳动物宿主体内的血液和组织间隙中进行细胞外增殖。它们通过顺序改变其变异表面糖蛋白（VSG）来逃避宿主的抗体介导的裂解。VSG 紧密覆盖整个寄生虫体，作为物理屏障。在布氏锥虫和密切相关的物种伊氏锥虫、马媾疫锥虫中，每个 VSG 多肽可以根据半胱氨酸分布和序列同源性分为 N-和 C-末端结构域。N-末端结构域是抗原变异的基础，高度可变，包含所有暴露的表位；C-末端结构域相对保守，通常观察到完整的四或八个半胱氨酸。我们利用 VSG 特异性引物通过 RT-PCR 从两种不同的伊氏锥虫变体中克隆了两个基因。一个包含 A 型 VSG N-末端结构域，后面是缺乏半胱氨酸残基的 C-末端结构域。为了确认该基因表达为功能性 VSG，我们使用 Western 印迹和活锥虫的免疫荧光染色来表征相应基因产物的表达和定位。表达分析表明，该蛋白高度表达、具有变异性且具有普遍的细胞表面定位。所有这些结果表明它被表达为功能性 VSG。我们的发现表明 VSG C-末端结构域中的半胱氨酸残基不是必需的；类似于 T. brucei 的 VSG 的保守 C-末端结构域可能会进化以调节 VSG 的表达。
