The tripartite motif (TRIM) protein family is an E3 ubiquitin ligase family. Recent reports have indicated that some TRIM proteins have antiviral functions, especially against retroviruses. However, most studies mainly focus on the relationship between TRIM21 and interferon or other antiviral effectors. The effect of TRIM21 on virus-encoded proteins remains unclear. In this study, we screened candidate interacting proteins of HBV DNA polymerase (Pol) by FLAG affinity purification and mass spectrometry assay and identified TRIM21 as its regulator. We used a coimmunoprecipitation (co-IP) assay to demonstrate that TRIM21 interacted with the TP domain of HBV DNA Pol. In addition, TRIM21 promoted the ubiquitination and degradation of HBV DNA Pol using its RING domain, which has E3 ubiquitin ligase activity. Lys260 and Lys283 of HBV DNA Pol were identified as targets for ubiquitination mediated by TRIM21. Finally, we uncovered that TRIM21 degrades HBV DNA Pol to restrict HBV DNA replication, and its SPRY domain is critical for this activity. Taken together, our results indicate that TRIM21 suppresses HBV DNA replication mainly by promoting the ubiquitination of HBV DNA Pol, which may provide a new potential target for the treatment of HBV.

中文翻译：

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E3泛素连接酶TRIM21促进HBV DNA聚合酶降解。

三重基序（TRIM）蛋白家族是E3泛素连接酶家族。最近的报道表明，某些TRIM蛋白具有抗病毒功能，尤其是针对逆转录病毒。但是，大多数研究主要集中在TRIM21与干扰素或其他抗病毒效应物之间的关系。TRIM21对病毒编码蛋白的作用尚不清楚。在这项研究中，我们通过FLAG亲和纯化和质谱分析法筛选了HBV DNA聚合酶（Pol）的候选相互作用蛋白，并确定了TRIM21作为其调节剂。我们使用了免疫共沉淀（co-IP）测定法来证明TRIM21与HBV DNA Pol的TP结构域相互作用。此外，TRIM21利用其具有E3泛素连接酶活性的RING域促进了HBV DNA Pol的泛素化和降解。HBV DNA Pol的Lys260和Lys283被确定为TRIM21介导的泛素化的靶标。最后，我们发现TRIM21降解HBV DNA Pol以限制HBV DNA复制，而其SPRY结构域对该活性至关重要。两者合计，我们的结果表明TRIM21主要通过促进HBV DNA Pol的泛素化来抑制HBV DNA复制，这可能为HBV的治疗提供新的潜在靶标。