Effects of an Early Conformational Switch Defect during ϕX174 Morphogenesis Are Belatedly Manifested Late in the Assembly Pathway
Effects of an Early Conformational Switch Defect during ϕX174 Morphogenesis Are Belatedly Manifested Late in the Assembly Pathway
复制标题
phiX174 形态发生过程中早期构象转换缺陷的影响在组装途径的后期才显现出来
作者：
E. Gordon;B. Fane
摘要：在病毒外壳蛋白中，c端芳香氨基酸介导了病毒外壳蛋白的构象开关。这些开关引导外壳蛋白通过早期组装。除了芳香氨基酸外，两个酸性残基，D111和E113，与基本的外壳蛋白侧链形成盐桥。虽然盐桥的形成似乎不是组装的关键，但芳香氨基酸取代D111产生了致死表型。该侧链独特地朝向衣架结合袋的中心，其主要由芳香环-环相互作用主导。因此，D111Y取代可以重构口袋触点。先前表征的B -突变体在原衣壳形成之前阻断了组装。然而，D111Y突变体产生了一个组装颗粒，其中包含结构蛋白和外部支架蛋白，但缺乏蛋白B和DNA。外部支架蛋白内的抑制因子介导颗粒形态发生的后期阶段，恢复了生存能力。后原壳颗粒的独特形成和新的抑制因子可能表明新的B蛋白功能。然而，遗传数据表明，该颗粒代表了早期组装错误的延迟表现。这种看似晚起作用的缺陷被先前描述的早期，前衣壳，B -组装突变的抑制子所挽救，这些抑制子作用于外壳蛋白柔韧性水平。同样，新分离的外支架蛋白抑制因子也表现出全局抑制表型。因此，从感染细胞中分离出的非通路产物可能不能准确反映初始缺陷的时间性质。
ABSTRACT C-terminal, aromatic amino acids in the ϕX174 internal scaffolding protein B mediate conformational switches in the viral coat protein. These switches direct the coat protein through early assembly. In addition to the aromatic amino acids, two acidic residues, D111 and E113, form salt bridges with basic, coat protein side chains. Although salt bridge formation did not appear to be critical for assembly, the substitution of an aromatic amino acid for D111 produced a lethal phenotype. This side chain is uniquely oriented toward the center of the coat-scaffolding binding pocket, which is heavily dominated by aromatic ring-ring interactions. Thus, the D111Y substitution may restructure pocket contacts. Previously characterized B − mutants blocked assembly before procapsid formation. However, the D111Y mutant produced an assembled particle, which contained the structural and external scaffolding proteins but lacked protein B and DNA. A suppressor within the external scaffolding protein, which mediates the later stages of particle morphogenesis, restored viability. The unique formation of a postprocapsid particle and the novel suppressor may be indicative of a novel B protein function. However, genetic data suggest that the particle represents the delayed manifestation of an early assembly error. This seemingly late-acting defect was rescued by previously characterized suppressors of early, preprocapsid, B − assembly mutations, which act on the level of coat protein flexibility. Likewise, the newly isolated suppressor in the external scaffolding protein also exhibited a global suppressing phenotype. Thus, the off-pathway product isolated from infected cells may not accurately reflect the temporal nature of the initial defect.
支架和外壳蛋白对噬菌体原衣壳组装的能量贡献。
影响因子：
3.7
作者：
Zlotnick,Adam;Suhanovsky,MargaretM;Teschke,CarolynM
通讯作者：
Teschke,CarolynM