Ostapchuk Philomena, Suomalainen Maarit, Zheng Yueting, Boucke Karin, Greber Urs F, Hearing Patrick
Department of Molecular Genetics and Microbiology, School of Medicine, Stony Brook University, Stony Brook, NY, United States of America.
Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland.
PLoS Pathog. 2017 Jun 19;13(6):e1006455. doi: 10.1371/journal.ppat.1006455. eCollection 2017 Jun.
The Adenovirus (Ad) genome within the capsid is tightly associated with a virus-encoded, histone-like core protein-protein VII. Two other Ad core proteins, V and X/μ, also are located within the virion and are loosely associated with viral DNA. Core protein VII remains associated with the Ad genome during the early phase of infection. It is not known if naked Ad DNA is packaged into the capsid, as with dsDNA bacteriophage and herpesviruses, followed by the encapsidation of viral core proteins, or if a unique packaging mechanism exists with Ad where a DNA-protein complex is simultaneously packaged into the virion. The latter model would require an entirely new molecular mechanism for packaging compared to known viral packaging motors. We characterized a virus with a conditional knockout of core protein VII. Remarkably, virus particles were assembled efficiently in the absence of protein VII. No changes in protein composition were evident with VII-virus particles, including the abundance of core protein V, but changes in the proteolytic processing of some capsid proteins were evident. Virus particles that lack protein VII enter the cell, but incoming virions did not escape efficiently from endosomes. This greatly diminished all subsequent aspects of the infectious cycle. These results reveal that the Ad major core protein VII is not required to condense viral DNA within the capsid, but rather plays an unexpected role during virus maturation and the early stages of infection. These results establish a new paradigm pertaining to the Ad assembly mechanism and reveal a new and important role of protein VII in early stages of infection.
衣壳内的腺病毒（Ad）基因组与一种病毒编码的、组蛋白样核心蛋白——蛋白VII紧密相关。另外两种腺病毒核心蛋白，蛋白V和蛋白X/μ，也位于病毒粒子内，并且与病毒DNA松散结合。在感染早期，核心蛋白VII仍与腺病毒基因组结合。目前尚不清楚裸露的腺病毒DNA是否像双链DNA噬菌体和疱疹病毒那样先被包装进衣壳，随后再包裹病毒核心蛋白，或者腺病毒是否存在一种独特的包装机制，即DNA-蛋白复合物同时被包装进病毒粒子。与已知的病毒包装机制相比，后一种模型需要全新的分子包装机制。我们对一种核心蛋白VII条件性敲除的病毒进行了特性分析。值得注意的是，在没有蛋白VII的情况下，病毒粒子仍能高效组装。VII型病毒粒子的蛋白质组成没有明显变化，包括核心蛋白V的丰度，但一些衣壳蛋白的蛋白水解加工过程有明显变化。缺乏蛋白VII的病毒粒子能够进入细胞，但进入的病毒粒子不能有效地从内体中逃逸。这极大地削弱了感染周期的所有后续环节。这些结果表明，腺病毒主要核心蛋白VII并非衣壳内浓缩病毒DNA所必需，而是在病毒成熟和感染早期发挥了意想不到的作用。这些结果确立了有关腺病毒组装机制的新范式，并揭示了蛋白VII在感染早期的新的重要作用。
