Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, NE 68583-0900, USA.
Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE 68583-0722, USA.
Viruses. 2021 Apr 28;13(5):782. doi: 10.3390/v13050782.
Chloroviruses are unusual among viruses infecting eukaryotic organisms in that they must, like bacteriophages, penetrate a rigid cell wall to initiate infection. PBCV-1 infects its host, NC64A by specifically binding to and degrading the cell wall of the host at the point of contact by a virus-packaged enzyme(s). However, PBCV-1 does not use any of the five previously characterized virus-encoded polysaccharide degrading enzymes to digest the host cell wall during virus entry because none of the enzymes are packaged in the virion. A search for another PBCV-1-encoded and virion-associated protein identified protein A561L. The fourth domain of A561L is a 242 amino acid C-terminal domain, named A561L, with cell wall degrading activity. An A561L homolog was present in all 52 genomically sequenced chloroviruses, infecting four different algal hosts. A561L degraded the cell walls of all four chlorovirus hosts, as well as several non-host spp. Thus, A561L was not cell-type specific. Finally, we discovered that exposure of highly purified PBCV-1 virions to A561L increased the specific infectivity of PBCV-1 from about 25-30% of the particles forming plaques to almost 50%. We attribute this increase to removal of residual host receptor that attached to newly replicated viruses in the cell lysates.
噬藻体是感染真核生物的病毒中较为特殊的一类，因为它们必须像噬菌体一样穿透坚硬的细胞壁才能开始感染。PBCV-1 通过特定的结合和降解作用感染其宿主 NC64A，即在病毒接触点处降解宿主细胞壁。然而，PBCV-1 在病毒进入宿主细胞时并不使用之前鉴定的五种病毒编码的多糖降解酶来消化宿主细胞壁，因为这些酶都没有包装在病毒粒子中。对另一种 PBCV-1 编码的、与病毒粒子相关的蛋白的搜索发现了蛋白 A561L。A561L 的第四结构域是一个 242 个氨基酸的 C 末端结构域，命名为 A561L，具有细胞壁降解活性。A561L 同源物存在于感染四种不同藻类宿主的所有 52 种基因组测序的噬藻体中。A561L 降解了所有四种噬藻体宿主的细胞壁，以及几种非宿主 spp。因此，A561L 没有细胞类型特异性。最后，我们发现，将高度纯化的 PBCV-1 病毒粒子暴露于 A561L 中，可使 PBCV-1 的特异性感染力从大约 25-30%形成噬菌斑的颗粒增加到近 50%。我们将这种增加归因于去除了细胞裂解物中附着在新复制病毒上的残留宿主受体。
