Abstract

The diverse viruses in the phylum Nucleocytoviricota (also known as NLCDVs, Nucleo-cytoplasmic Large DNA Viruses) typically possess large icosahedral virions. However, in several families of Nucleocytoviricota, the icosahedral capsid was replaced by irregular particle shapes, most notably, the amphora-like virions of pandoraviruses and pithoviruses, the largest known virus particles in the entire virosphere. Pandoraviruses appear to be the most highly derived viruses in this phylum because their evolution involved not only the change in the virion shape, but also, the actual loss of the gene encoding double-jelly roll major capsid protein (DJR MCP), the main building block of icosahedral capsids in this virus assemblage. Instead, pandoravirus virions are built of unrelated abundant proteins. Here we show that the second most abundant virion protein of pandoraviruses, major virion protein 2 (MVP2), evolved from an inactivated derivative of a bacterial glycoside hydrolase of the GH16 family. The ancestral form of MVP2 was apparently acquired early in the evolution of the Nucleocytoviricota, to become a minor virion protein. After a duplication in the common ancestor of pandoraviruses and molliviruses, one of the paralogs displaces DJR MCP in pandoraviruses, conceivably, opening the way for a major increase in the size of the virion and the genome. Exaptation of a carbohydrate-binding protein for the function of the MVP is a general trend in virus evolution and might underlie the transformation of the virion shape in other groups of the Nucleocytoviricota as well.

中文翻译：

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从灭活的细菌糖苷水解酶进化出巨型潘多拉病毒的主要病毒体蛋白

摘要

Nucleocytoviricota门中的多种病毒（也称为 NLCDV，核质大 DNA 病毒）通常具有大的二十面体病毒体。然而，在几个核细胞病毒科，二十面体衣壳被不规则的颗粒形状所取代，最引人注目的是潘多拉病毒和皮托病毒的双耳瓶状病毒体，这是整个病毒圈中已知的最大的病毒颗粒。潘多拉病毒似乎是该门中衍生度最高的病毒，因为它们的进化不仅涉及病毒粒子形状的变化，而且还涉及编码双层果冻卷主要衣壳蛋白 (DJR MCP) 的基因的实际丢失，主要建筑该病毒组合中的二十面体衣壳块。相反，潘多拉病毒病毒粒子是由不相关的丰富蛋白质构成的。在这里，我们显示潘多拉病毒中第二丰富的病毒粒子蛋白，主要病毒粒子蛋白 2 (MVP2)，是从 GH16 家族的细菌糖苷水解酶的失活衍生物进化而来的。Nucleocytoviricota，成为次要病毒粒子蛋白。在潘多拉病毒和莫利病毒的共同祖先中复制后，其中一个旁系同源物取代了潘多拉病毒中的 DJR MCP，可以想象，这为病毒体和基因组大小的大幅增加开辟了道路。对 MVP 功能的碳水化合物结合蛋白的扩展是病毒进化的普遍趋势，并且可能是其他核细胞病毒组中病毒粒子形状转变的基础。