The most prominent defence of the unicellular parasite Trypanosoma brucei against the host immune system is a dense coat that comprises a variant surface glycoprotein (VSG). Despite the importance of the VSG family, no complete structure of a VSG has been reported. Making use of high-resolution structures of individual VSG domains, we employed small-angle X-ray scattering to elucidate the first two complete VSG structures. The resulting models imply that the linker regions confer great flexibility between domains, which suggests that VSGs can adopt two main conformations to respond to obstacles and changes of protein density, while maintaining a protective barrier at all times. Single-molecule diffusion measurements of VSG in supported lipid bilayers substantiate this possibility, as two freely diffusing populations could be detected. This translates into a highly flexible overall topology of the surface VSG coat, which displays both lateral movement in the plane of the membrane and variation in the overall thickness of the coat.

中文翻译：

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动态锥虫变体表面糖蛋白涂层的屏蔽功能的结构基础。

单细胞寄生性布鲁氏锥虫对宿主免疫系统的最显着防御是致密的被膜，其包含变体表面糖蛋白（VSG）。尽管VSG系列很重要，但尚未报告VSG的完整结构。利用各个VSG域的高分辨率结构，我们采用了小角度X射线散射来阐明前两个完整的VSG结构。所得模型暗示接头区域在结构域之间赋予很大的灵活性，这表明VSG可以采用两种主要构象来响应障碍和蛋白质密度的变化，同时始终保持保护性障碍。VSG在支持的脂质双层中的单分子扩散测量证实了这种可能性，因为可以检测到两个自由扩散的种群。