Repression of gene transcription by nuclear receptors is mediated by interactions with co-repressor proteins such as SMRT and N-CoR1,2, which in turn recruit histone deacetylases to the chromatin3,4,5. Aberrant interactions between nuclear receptors and co-repressors contribute towards acute promyelocytic leukaemia and thyroid hormone resistance syndrome6,7,8. The binding of co-repressors to nuclear receptors occurs in the unliganded state, and can be stabilized by antagonists9. Here we report the crystal structure of a ternary complex containing the peroxisome proliferator-activated receptor-α ligand-binding domain bound to the antagonist GW6471 and a SMRT co-repressor motif. In this structure, the co-repressor motif adopts a three-turn α-helix that prevents the carboxy-terminal activation helix (AF-2) of the receptor from assuming the active conformation. Binding of the co-repressor motif is further reinforced by the antagonist, which blocks the AF-2 helix from adopting the active position. Biochemical analyses and structure-based mutagenesis indicate that this mode of co-repressor binding is highly conserved across nuclear receptors.
核受体对
基因转录的抑制是通过与共同抑制蛋白(如SMRT和N-CoR)相互作用来介导的,这些共同抑制蛋白反过来招募组蛋白
去乙酰化酶到染色质上。核受体和共同抑制因子之间的异常相互作用与急性早幼粒细胞白血病和甲状腺激素抵抗综合症有关。共同抑制因子与核受体的结合发生在未结合
配体的状态,并可被拮抗剂稳定。在这里,我们报告了一种三元复合物的晶体结构,该复合物包含
过氧化物酶体增殖物激活受体-α的
配体结合域,与拮抗剂GW6471和SMRT共同抑制基序结合。在这个结构中,共同抑制基序呈现出一个三圈的α-螺旋,阻止受体的羧基末端激活螺旋(AF-2)呈现活性构象。拮抗剂进一步增强了共同抑制基序的结合,阻止AF-2螺旋采纳主动位置。生化分析和基于结构的突变实验表明,这种共同抑制基序的结合模式在核受体中高度保守。