附属蛋白：冠状病毒不容忽视的一类蛋白

Accessory proteins: a type of protein that cannot be neglected in coronaviruses

摘要:

冠状病毒（Coronaviruses，CoVs）是基因组最大的一类单股正链RNA病毒，多数可以跨物种传播并感染人类，是当前引起重大公共卫生事件、严重威胁人类健康的病原之一。病毒基因组全长约25—31 kb，编码多个非结构蛋白、结构蛋白（S、E、M、N）及附属蛋白。对于大多数冠状病毒来说，附属蛋白虽然是病毒复制的非必需蛋白，但往往在病毒的致病过程中发挥重要作用，是冠状病毒重要的功能蛋白。该类蛋白位于病毒基因组的3'端，由位于基因起始位置的转录调控序列（Transcription Regulating Sequence，TRS）调控其mRNA的转录，而且蛋白编码序列的密码子使用偏爱性对蛋白翻译也产生重要影响。附属蛋白具有跨膜蛋白的属性和独特的蛋白转运基序，后者对该类蛋白跨膜区的形成、拓扑学结构及蛋白的细胞内运输过程起决定性的作用，从而直接影响附属蛋白的功能。本文首先总结了冠状病毒最新的分类及基因组结构；然后从附属蛋白的种类、功能、蛋白转运基序、拓扑学结构及密码子使用偏爱性等方面系统概述了相关研究进展，并对下一步的研究方向进行了展望，为更加全面地认识冠状病毒附属蛋白的生物学特性提供重要参考。

关键词:冠状病毒;附属蛋白;细胞内转运;拓扑学;密码子使用偏爱性

Abstract:

Coronaviruses (CoVs) are a group of positive-sense, single-stranded RNA viruses with the largest genome, most of which can spread across species and infect humans. Some of the pathogens in the group are causing major public health problems and seriously threatening human health. The full-length genome of the viruses is about 25—31 kb in length, encoding multiple nonstructural, structural proteins (S, E, M, and N) and accessory proteins. For most coronaviruses, their accessory proteins are not indispensable for viral replication, but they are often involved in pathogenesis in hosts and act as functional proteins. These accessory protein genes are located at the 3' end of the viral genomes. Expression of these genes can be regulated at transcription level by the transcription regulating sequence (TRS) which locates at the beginning of the genes or at translation level by the codon usage bias of the protein-coding sequences. The accessory proteins belong to trans-membrane protein and carry unique protein transport motifs. These characters play decisive role for the formation of unique topological structures and intracellular transport of the proteins, thus directly affect their functions. A summary of the latest classification and genome structure of coronaviruses was made in the beginning of the article; then roles, categorization, protein transport motifs, topological structures and codon usage bias of the accessory proteins were discussed individually and prospects of research in the field were foreseen as well, aiming to help understand the biological characteristics of this category of proteins.

Key words:coronaviruses;accessory proteins;cellular transport;topology;codon usage bias