‡Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA, U.S.A.
Biochem J. 2013 Dec 1;456(2):231-40. doi: 10.1042/BJ20121425.
TRIM (tripartite motif) proteins primarily function as ubiquitin E3 ligases that regulate the innate immune response to infection. TRIM25 [also known as Efp (oestrogen-responsive finger protein)] has been implicated in the regulation of oestrogen receptor α signalling and in the regulation of innate immune signalling via RIG-I (retinoic acid-inducible gene-I). RIG-I senses cytosolic viral RNA and is subsequently ubiquitinated by TRIM25 at its N-terminal CARDs (caspase recruitment domains), leading to type I interferon production. The interaction with RIG-I is dependent on the TRIM25 B30.2 domain, a protein-interaction domain composed of the PRY and SPRY tandem sequence motifs. In the present study we describe the 1.8 Å crystal structure of the TRIM25 B30.2 domain, which exhibits a typical B30.2/SPRY domain fold comprising two N-terminal α-helices, thirteen β-strands arranged into two β-sheets and loop regions of varying lengths. A comparison with other B30.2/SPRY structures and an analysis of the loop regions identified a putative binding pocket, which is likely to be involved in binding target proteins. This was supported by mutagenesis and functional analyses, which identified two key residues (Asp(488) and Trp(621)) in the TRIM25 B30.2 domain as being critical for binding to the RIG-I CARDs.
TRIM（三基序）蛋白主要作为泛素 E3 连接酶发挥作用，调节对感染的先天免疫反应。TRIM25[也称为 Efp（雌激素反应指蛋白）]已被牵连到雌激素受体 α 信号的调节和 RIG-I（维甲酸诱导基因-I）的先天免疫信号的调节中。RIG-I 感知细胞溶质中的病毒 RNA，随后被 TRIM25 在其 N 端 CARD（半胱氨酸天冬氨酸蛋白酶募集结构域）处泛素化，导致 I 型干扰素的产生。与 RIG-I 的相互作用依赖于 TRIM25 的 B30.2 结构域，该结构域是由 PRY 和 SPRY 串联序列基序组成的蛋白质相互作用结构域。在本研究中，我们描述了 TRIM25 B30.2 结构域的 1.8Å 晶体结构，该结构域表现出典型的 B30.2/SPRY 结构域折叠，包含两个 N 端α-螺旋、十三个β-链，排列成两个β-片和不同长度的环区。与其他 B30.2/SPRY 结构的比较和环区的分析确定了一个可能的结合口袋，该口袋可能参与与靶蛋白的结合。这得到了突变和功能分析的支持，该分析确定了 TRIM25 B30.2 结构域中的两个关键残基（天冬氨酸 488 和色氨酸 621）对于与 RIG-I CARDs 的结合至关重要。
