Gan Lu, Speir Jeffrey A, Conway James F, Lander Gabriel, Cheng Naiqian, Firek Brian A, Hendrix Roger W, Duda Robert L, Liljas Lars, Johnson John E
Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Structure. 2006 Nov;14(11):1655-65. doi: 10.1016/j.str.2006.09.006.
Maturation of the bacteriophage HK97 capsid from a precursor (Prohead II) to the mature state (Head II) involves a 60 A radial expansion. The mature particle is formed by 420 copies of the major capsid protein organized on a T = 7 laevo lattice with each subunit covalently crosslinked to two neighbors. Well-characterized pH 4 expansion intermediates make HK97 valuable for investigating quaternary structural dynamics. Here, we use X-ray crystallography and cryo-EM to demonstrate that in the final transition in maturation (requiring neutral pH), pentons in Expansion Intermediate IV (EI-IV) reversibly sample 14 A translations and 6 degrees rotations relative to a fixed hexon lattice. The limit of this trajectory corresponds to the Head II conformation that is secured at this extent only by the formation of the final class of covalent crosslinks. Mutants that cannot crosslink or EI-IV particles that have been rendered incapable of forming the final crosslink remain in the EI-IV state.
噬菌体HK97衣壳从前体（原头部II）成熟为成熟状态（头部II）涉及60埃的径向扩张。成熟颗粒由420个主要衣壳蛋白拷贝组成，这些蛋白排列在T = 7左旋晶格上，每个亚基与两个相邻亚基共价交联。特征明确的pH 4扩张中间体使HK97对于研究四级结构动力学具有重要价值。在这里，我们使用X射线晶体学和冷冻电镜来证明，在成熟的最终转变（需要中性pH）中，扩张中间体IV（EI-IV）中的五聚体相对于固定的六聚体晶格可逆地进行14埃的平移和6度的旋转。该轨迹的极限对应于头部II构象，该构象仅通过形成最后一类共价交联在这个程度上得以固定。无法交联的突变体或已无法形成最终交联的EI-IV颗粒保持在EI-IV状态。
