Woodbury Brianna M, Newcomer Rebecca L, Alexandrescu Andrei T, Teschke Carolyn M
Department of Molecular and Cell Biology, University of Connecticut, 91 N. Eagleville Rd, Storrs, CT, 06269-3125, USA.
Department of Chemistry, University of Connecticut, 55 N. Eagleville Rd, Storrs, CT, 06269-3060, USA.
bioRxiv. 2024 Sep 8:2024.09.08.611893. doi: 10.1101/2024.09.08.611893.
The 134-residue phage L decoration protein (Dec) forms a capsid-stabilizing homotrimer that has an asymmetric tripod-like structure when bound to phage L capsids. The N-termini of the trimer subunits consist of spatially separated globular OB-fold domains that interact with the virions of phage L or the related phage P22. The C-termini of the trimer form a three-stranded intertwined spike structure that accounts for nearly all the interactions that stabilize the trimer. A Dec mutant with the spike residues 99-134 deleted (Dec ) was used to demonstrate that the stable globular OB-fold domain folds independently of the C-terminal residues. However, Dec was unable to bind phage P22 virions, indicating the C-terminal spike is essential for stable capsid interaction. The full-length Dec trimer is disassembled into monomers by acidification to pH <2. These monomers retain the folded globular OB-fold domain structure, but the spike is unfolded. Increasing the pH of the Dec monomer solution to pH 6 allowed for slow trimer formation over the course of days. The infectious cycle of phage L is only around an hour, however, implying Dec trimer assembly is templated by the phage capsid. The Thermodynamic Hypothesis holds that protein folding is determined by the amino acid sequence. Dec serves as an unusual example of an oligomeric folding step that is kinetically accelerated by a viral capsid template. The capsid templating mechanism could satisfy the flexibility needed for Dec to adapt to the unusual quasi-symmetric binding site on the mature phage L capsid.
134个氨基酸残基的噬菌体L装饰蛋白（Dec）形成一种稳定衣壳的同三聚体，当其与噬菌体L衣壳结合时具有不对称的三脚架状结构。三聚体亚基的N端由空间上分离的球状OB折叠结构域组成，这些结构域与噬菌体L或相关噬菌体P22的病毒粒子相互作用。三聚体的C端形成一个三链交织的刺突结构，几乎所有稳定三聚体的相互作用都归因于此。一个缺失刺突残基99 - 134的Dec突变体（Dec ）被用于证明稳定的球状OB折叠结构域的折叠独立于C端残基。然而，Dec 无法结合噬菌体P22病毒粒子，这表明C端刺突对于稳定的衣壳相互作用至关重要。通过酸化至pH <2，全长Dec三聚体被拆解成单体。这些单体保留了折叠的球状OB折叠结构域，但刺突是展开的。将Dec单体溶液的pH提高到6，在数天时间内允许缓慢形成三聚体。然而，噬菌体L的感染周期仅约一小时，这意味着Dec三聚体的组装是由噬菌体衣壳作为模板的。热力学假说认为蛋白质折叠由氨基酸序列决定。Dec是寡聚折叠步骤的一个不同寻常的例子，其在动力学上由病毒衣壳模板加速。衣壳模板机制可以满足Dec适应成熟噬菌体L衣壳上不寻常的准对称结合位点所需的灵活性。
