Woodson Michael, Prokhorov Nikolai S, Scott Seth D, Zhao Wei, Zhang Wei, Choi Kyung H, Jardine Paul J, Morais Marc C
Sealy Center for Structural Biology, The University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA.
Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA.
Sci Adv. 2025 Mar 21;11(12):eadk8779. doi: 10.1126/sciadv.adk8779. Epub 2025 Mar 19.
The self-assembly of bacteriophage capsids from major capsid proteins (MCPs) and scaffolding proteins (SPs) and the subsequent expansion of these capsids are essential steps in bacteriophage life cycles. However, the mechanism by which assembly occurs remains poorly understood, and few intermediate states are available to illuminate the expansion of meta-stable procapsids into robust mature capsids. Here, we present the structure of a partially expanded phi29 procapsid that reveals distinct conformations of MCPs and allows visualization of SPs in multiple oligomeric states. These results suggest that formation of SP dimers, tetramers, and higher-order oligomers drives dissociation of SP from MCP to actuate capsid expansion. Hexons expand first, and we propose penton maturation is delayed by a symmetry match with SP oligomers. We further show that the prolate shape of phi29's capsid is possible due to concave hexons in the equatorial region of the capsid that may alter interactions with SP and explain the observed dependence of the prolate shape on SP.
噬菌体衣壳由主要衣壳蛋白（MCP）和支架蛋白（SP）自组装而成，随后这些衣壳的扩张是噬菌体生命周期中的关键步骤。然而，衣壳组装发生的机制仍知之甚少，并且几乎没有中间状态可用于阐明亚稳态前衣壳向坚固成熟衣壳的扩张过程。在此，我们展示了部分扩张的phi29前衣壳的结构，该结构揭示了MCP的不同构象，并使多种寡聚状态下的SP可视化。这些结果表明，SP二聚体、四聚体和高阶寡聚体的形成驱动SP从MCP解离，从而启动衣壳扩张。六邻体首先扩张，我们提出五邻体成熟因与SP寡聚体的对称匹配而延迟。我们进一步表明，phi29衣壳的长形形状是可能的，这是由于衣壳赤道区域的凹面六邻体可能改变与SP的相互作用，并解释了观察到的长形形状对SP的依赖性。
