Sulfolobus turreted icosahedral virus (STIV) is a model archaeal virus and member of the PRD1-adenovirus lineage. Although STIV employs pyramidal lysis structures to exit the host, knowledge of the viral entry process is lacking. We therefore initiated studies on STIV attachment and entry. Negative stain and cryoelectron micrographs showed virion attachment to pili-like structures emanating from the Sulfolobus host. Tomographic reconstruction and sub-tomogram averaging revealed pili recognition by the STIV C381 turret protein. Specifically, the triple jelly roll structure of C381 determined by X-ray crystallography shows that pilus recognition is mediated by conserved surface residues in the second and third domains. In addition, the STIV petal protein (C557), when present, occludes the pili binding site, suggesting that it functions as a maturation protein. Combined, these results demonstrate a role for the namesake STIV turrets in initial cellular attachment and provide the first molecular model for viral attachment in the archaeal domain of life.

中文翻译：

---

古细菌病毒细胞附着的分子机制。

磺化炮塔二十面体病毒（STIV）是一种古细菌模型病毒，是PRD1腺病毒谱系的成员。尽管STIV采用金字塔形裂解结构退出宿主，但缺乏病毒进入过程的知识。因此，我们开始了关于STIV附着和进入的研究。负染色和低温电子显微照片显示，病毒体附着在由Sulfolobus宿主发出的菌毛样结构上。体层摄影术重建和断层摄影平均显示STIV C381炮塔蛋白可识别菌毛。具体地，通过X射线晶体学确定的C381的三重果冻卷结构显示菌毛识别是由第二和第三结构域中保守的表面残基介导的。此外，STIV花瓣蛋白（C557）（如果存在）会阻塞菌毛结合位点，提示它起着成熟蛋白的作用。综合起来，这些结果证明了同名STIV炮塔在初始细胞附着中的作用，并为生命古细菌域中的病毒附着提供了第一个分子模型。