The Herpes Simplex Virus Protein pUL31 Escorts Nucleocapsids to Sites of Nuclear Egress, a Process Coordinated by Its N-Terminal Domain.
The Herpes Simplex Virus Protein pUL31 Escorts Nucleocapsids to Sites of Nuclear Egress, a Process Coordinated by Its N-Terminal Domain.
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DOI：
10.1371/journal.ppat.1004957
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发表时间：
2015-06
期刊：
影响因子：
6.7
通讯作者：
Bailer SM
中科院分区：
文献类型：
--
作者：
Funk C;Ott M;Raschbichler V;Nagel CH;Binz A;Sodeik B;Bauerfeind R;Bailer SM
疱疹病毒的子代衣壳通过核膜出芽离开细胞核。两种病毒蛋白质，膜蛋白pUL34和核磷蛋白pUL31，形成衣壳排出细胞核所需的核排出复合物。所有pUL31直向同源物都由具有1至3个基本补丁的不同N-末端结构域和保守的C-末端结构域组成。为了破译N-末端结构域的功能，我们已经产生了几个单纯疱疹病毒突变体，并在这里显示，pUL31的N-末端结构域是必不可少的基本补丁是至关重要的病毒繁殖。pUL 31和pUL 34通过不同的途径彼此独立地进入细胞核，并且需要pUL 31的N-末端结构域来防止它们在细胞质中的过早相互作用。出乎意料的是，pUL31的核输入不需要嵌入该结构域中的经典的二分核定位信号。在细胞核中，pUL 31与核膜和新形成的衣壳结合。病毒突变体缺乏N-末端结构域或其基本补丁中和仍然与核衣壳，但无法将它们转移到核膜。用一种新的人工贴片代替真实的基本贴片，产生了HSV1（17+）Lox-UL31-hbpmp1mp2，它是可行的，但延迟了核出口，并损害了病毒的生产。因此，虽然pUL31的C-末端结构域足以与核衣壳相互作用，但N-末端结构域对于衣壳易位到核出口位点以及与pUL34的协调相互作用是必需的。我们的数据表明，一个精心策划的事件序列与pUL 31结合到核衣壳，并护送他们到内核被膜。我们提出了一个共同的机制疱疹病毒核出口：pUL 31是所需的核内易位的核衣壳和随后的相互作用pUL 34，从而耦合衣壳成熟与初级的免疫。疱疹病毒衣壳的装配在宿主细胞核中启动。由于大小的限制，新形成的核衣壳不能通过核孔复合物离开核。相反，疱疹病毒应用一种进化上保守的机制来进行衣壳的核输出，称为核出口。该过程通过衣壳在内核膜处对接、有包膜的衣壳出芽到核周空间中、随后衣壳脱附并释放到细胞质中而开始，在细胞质中发生进一步成熟。在疱疹病毒家族中保守的两种病毒蛋白，膜蛋白pUL 34和磷蛋白pUL 31形成了对原发性疱疹至关重要的核出口复合物。我们在这里表明pUL 31和pUL 34彼此独立地进入细胞核。pUL31靶向核质，在那里它通过保守的C-末端结构域结合核衣壳，而其N-末端结构域对于衣壳易位到核膜以及对于与pUL34的协调相互作用是重要的。我们的数据表明，一种机制，显然是保守的所有疱疹病毒与pUL 31护送核衣壳的核膜，以耦合衣壳成熟与主要的破坏。
Progeny capsids of herpesviruses leave the nucleus by budding through the nuclear envelope. Two viral proteins, the membrane protein pUL34 and the nucleo-phosphoprotein pUL31 form the nuclear egress complex that is required for capsid egress out of the nucleus. All pUL31 orthologs are composed of a diverse N-terminal domain with 1 to 3 basic patches and a conserved C-terminal domain. To decipher the functions of the N-terminal domain, we have generated several Herpes simplex virus mutants and show here that the N-terminal domain of pUL31 is essential with basic patches being critical for viral propagation. pUL31 and pUL34 entered the nucleus independently of each other via separate routes and the N-terminal domain of pUL31 was required to prevent their premature interaction in the cytoplasm. Unexpectedly, a classical bipartite nuclear localization signal embedded in this domain was not required for nuclear import of pUL31. In the nucleus, pUL31 associated with the nuclear envelope and newly formed capsids. Viral mutants lacking the N-terminal domain or with its basic patches neutralized still associated with nucleocapsids but were unable to translocate them to the nuclear envelope. Replacing the authentic basic patches with a novel artificial one resulted in HSV1(17+)Lox-UL31-hbpmp1mp2, that was viable but delayed in nuclear egress and compromised in viral production. Thus, while the C-terminal domain of pUL31 is sufficient for the interaction with nucleocapsids, the N-terminal domain was essential for capsid translocation to sites of nuclear egress and a coordinated interaction with pUL34. Our data indicate an orchestrated sequence of events with pUL31 binding to nucleocapsids and escorting them to the inner nuclear envelope. We propose a common mechanism for herpesviral nuclear egress: pUL31 is required for intranuclear translocation of nucleocapsids and subsequent interaction with pUL34 thereby coupling capsid maturation with primary envelopment. Herpesviral capsid assembly is initiated in the host nucleus. Due to size constraints, newly formed nucleocapsids are unable to leave the nucleus through the nuclear pore complex. Instead herpesviruses apply an evolutionarily conserved mechanism for nuclear export of capsids called nuclear egress. This process is initiated by docking of capsids at the inner nuclear membrane, budding of enveloped capsids into the perinuclear space followed by de-envelopment and release of capsids to the cytoplasm where further maturation occurs. Two viral proteins conserved throughout the herpesvirus family, the membrane protein pUL34 and the phosphoprotein pUL31 form the nuclear egress complex that is critical for primary envelopment. We show here that pUL31 and pUL34 enter the nucleus independently of each other. pUL31 is targeted to the nucleoplasm where it binds to nucleocapsids via the conserved C-terminal domain, while its N-terminal domain is important for capsid translocation to the nuclear envelope and for a coordinated interaction with pUL34. Our data suggest a mechanism that is apparently conserved among all herpesviruses with pUL31 escorting nucleocapsids to the nuclear envelope in order to couple capsid maturation with primary envelopment.