Small Ubiquitin-like Modifier蛋白質對Epstein-Barr病毒外鞘蛋白質BDLF1的調控

Epstein-Barr virus是人類第四型皰疹病毒，病毒外殼由162個次蛋白衣 (capsomer)組合而成正二十面體 (icosahedron)。EB病毒外殼由主要外鞘蛋白質VCA (major capsid protein)與次要外鞘蛋白質BDLF1和BORF1 (minor capsid protein)組成，兩分子的BDLF1與一分子的BORF1組成三聚體 (triplex)，連結VCA 形成的五聚體或六聚體以組成次蛋白衣，並由具有NLS的BORF1分別將BDLF1或VCA帶入核內進行病毒顆粒的組裝。在病毒成熟的過程中，外鞘蛋白質的組裝是非常重要的一環，卻是溶裂循環中最少被研究的部分。SUMO (small ubiquitin-like modifier) 以共價鍵結方式連接在目標蛋白質上是一種轉譯後修飾，參與許多蛋白質的功能調控，包括蛋白質在細胞中分佈的位置、轉錄活性、穩定度及與其他蛋白質的交互作用等。本研究首先發現，BDLF1與BORF1皆受到SUMO蛋白質共價鍵修飾，接著利用GST pull-down證明BDLF1利用其N端的SUMO-interaction motifs (SIMs)與SUMO蛋白質結合；以BDLF1的SIM突變株進行功能性分析後發現，SIM會增加BDLF1受SUMO蛋白質的修飾、降低受泛素化的程度，同時增進BDLF1的蛋白質穩定性；最後利用螢光顯微鏡分析則發現，當BDLF1的SIM突變會改變BDLF1與BORF1的分佈，所以BDLF1的SIM可能在EB病毒顆粒的組裝上扮演重要的角色。

關鍵字

人類第四型皰疹病毒；小類泛素；外鞘蛋白質

並列摘要

Epstein-Barr virus (EBV), also called human herpesvirus 4 (HHV-4), contains a common icosahedral structure with 162 capsomers. The capsids of EBV contain major capsid protein VCA and minor capsid proteins, BDLF1 and BORF1. The capsomers are composed of VCA pentamers or hexamers, which are linked together by triplexes that are formed by two copies of BDLF1 and one copy of BORF1. During the capsid assembly, BORF1, which exhibits nuclear localization signal sequence (NLS) brings VCA and BDLF1 into the nuclei. Assembly of capsid is required for the development of mature EBV virion but it is nevertheless the must unknown part of EBV lytic cycle. Targets covently attached by small ubiquitin-like modifier (SUMO) proteins is a kind of post-translational modification which involves in diverse functions of proteins including cellular localization, stability, transcriptional activity and protein-protein interaction. This study demonstrates that minor capsid proteins BDLF1 and BORF1 are both SUMOylated. A GST pulldown study identifies BDLF1 interacts noncolvently with SUMO through SUMO-interaction motifs (SIM) in the N-terminal region of BDLF1. Functional analysis of BDLF1 SIM mutants revealed that SIM integrity is required for increasing the SUMOylation level, decreasing the ubiquitination level as well as maintaining the stability of BDLF1. Futhermore, immunofluorescence analysis shows that BDLF1 SIM mutants exhibit different pattern with the colocalization of wt-BDLF1 and BORF1. These results indicate the SIM motifs in BDLF1 are likely to have a key function in the EBV capsid assembly.

並列關鍵字

Epstein-Barr virus ； SUMO ； BDLF1

參考文獻

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Small Ubiquitin-like Modifier蛋白質對Epstein-Barr病毒外鞘蛋白質BDLF1的調控

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