Dept. Biología Celular, Genética y Fisiología, Universidad de Málaga, Campus Teatinos, Málaga, Spain.
J Virol. 2011 Oct;85(19):9789-800. doi: 10.1128/JVI.02566-10. Epub 2011 Jul 20.
Geminiviruses are small DNA viruses that replicate in nuclei of infected plant cells by using plant DNA polymerases. These viruses encode a protein designated AL1, Rep, or AC1 that is essential for viral replication. AL1 is an oligomeric protein that binds to double-stranded DNA, catalyzes the cleavage and ligation of single-stranded DNA, and induces the accumulation of host replication machinery. It also interacts with several host proteins, including the cell cycle regulator retinoblastoma-related protein (RBR), the DNA replication protein PCNA (proliferating cellular nuclear antigen), and the sumoylation enzyme that conjugates SUMO to target proteins (SUMO-conjugating enzyme [SCE1]). The SCE1-binding motif was mapped by deletion to a region encompassing AL1 amino acids 85 to 114. Alanine mutagenesis of lysine residues in the binding region either reduced or eliminated the interaction with SCE1, but no defects were observed for other AL1 functions, such as oligomerization, DNA binding, DNA cleavage, and interaction with AL3 or RBR. The lysine mutations reduced or abolished virus infectivity in plants and viral DNA accumulation in transient-replication assays, suggesting that the AL1-SCE1 interaction is required for viral DNA replication. Ectopic AL1 expression did not result in broad changes in the sumoylation pattern of plant cells, but specific changes were detected, indicating that AL1 modifies the sumoylation state of selected host proteins. These results established the importance of AL1-SCE1 interactions during geminivirus infection of plants and suggested that AL1 alters the sumoylation of selected host factors to create an environment suitable for viral infection.
双生病毒是通过利用植物 DNA 聚合酶在感染植物细胞的核内进行复制的小型 DNA 病毒。这些病毒编码一种名为 AL1、Rep 或 AC1 的蛋白，该蛋白对病毒复制至关重要。AL1 是一种寡聚蛋白，能结合双链 DNA，催化单链 DNA 的切割和连接，并诱导宿主复制机制的积累。它还与几种宿主蛋白相互作用，包括细胞周期调节蛋白视网膜母细胞瘤相关蛋白 (RBR)、DNA 复制蛋白 PCNA（增殖细胞核抗原）和将 SUMO 连接到靶蛋白的 SUMO 连接酶 (SCE1)。通过删除，将 SCE1 结合基序映射到包含 AL1 氨基酸 85 到 114 的区域。该结合区域中赖氨酸残基的丙氨酸突变要么减少要么消除了与 SCE1 的相互作用，但对其他 AL1 功能（如寡聚化、DNA 结合、DNA 切割和与 AL3 或 RBR 的相互作用）没有观察到缺陷。赖氨酸突变减少或消除了病毒在植物中的感染性和瞬时复制试验中病毒 DNA 的积累，表明 AL1-SCE1 相互作用是病毒 DNA 复制所必需的。异位表达 AL1 不会导致植物细胞中泛素化模式的广泛变化，但检测到特定的变化，表明 AL1 改变了选定宿主蛋白的 SUMO 化状态。这些结果确立了 AL1-SCE1 相互作用在双生病毒感染植物过程中的重要性，并表明 AL1 改变了选定宿主因子的 SUMO 化，以创造适合病毒感染的环境。
