National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
Proc Natl Acad Sci U S A. 2013 Jul 23;110(30):12301-6. doi: 10.1073/pnas.1309947110. Epub 2013 Jul 9.
High-resolution structures of viruses have made important contributions to modern structural biology. Bacteriophages, the most diverse and abundant organisms on earth, replicate and infect all bacteria and archaea, making them excellent potential alternatives to antibiotics and therapies for multidrug-resistant bacteria. Here, we improved upon our previous electron cryomicroscopy structure of Salmonella bacteriophage epsilon15, achieving a resolution sufficient to determine the tertiary structures of both gp7 and gp10 protein subunits that form the T = 7 icosahedral lattice. This study utilizes recently established best practice for near-atomic to high-resolution (3-5 Å) electron cryomicroscopy data evaluation. The resolution and reliability of the density map were cross-validated by multiple reconstructions from truly independent data sets, whereas the models of the individual protein subunits were validated adopting the best practices from X-ray crystallography. Some sidechain densities are clearly resolved and show the subunit-subunit interactions within and across the capsomeres that are required to stabilize the virus. The presence of the canonical phage and jellyroll viral protein folds, gp7 and gp10, respectively, in the same virus suggests that epsilon15 may have emerged more recently relative to other bacteriophages.
病毒的高分辨率结构为现代结构生物学做出了重要贡献。噬菌体是地球上最多样化和最丰富的生物，能够复制和感染所有细菌和古菌，因此它们是抗生素和治疗多药耐药菌的理想替代品。在这里，我们改进了我们之前的沙门氏菌噬菌体 epsilon15 的电子冷冻显微镜结构，达到了足以确定形成 T = 7 二十面体晶格的 gp7 和 gp10 蛋白亚基的三级结构的分辨率。本研究利用了最近建立的用于近原子到高分辨率（3-5 Å）电子冷冻显微镜数据评估的最佳实践。通过从真正独立的数据集中进行多次重建，对密度图的分辨率和可靠性进行了交叉验证，而各个蛋白亚基的模型则通过 X 射线晶体学的最佳实践进行了验证。一些侧链密度清晰可辨，显示了衣壳内和衣壳之间稳定病毒所需的亚基-亚基相互作用。同一病毒中存在典型的噬菌体和果冻卷状病毒蛋白折叠，分别为 gp7 和 gp10，这表明 epsilon15 可能相对于其他噬菌体出现得更晚。
