Crystal structure of a Tankyrase-Axin complex and its implications for Axin turnover and Tankyrase substrate recruitment
Crystal structure of a Tankyrase-Axin complex and its implications for Axin turnover and Tankyrase substrate recruitment
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DOI：
10.1073/pnas.1116618109
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发表时间：
2012-01-31
影响因子：
11.1
通讯作者：
Xu, Wenqing
中科院分区：
文献类型：
--
作者：
Morrone, Seamus;Cheng, Zhihong;Xu, Wenqing
Axin 是一种肿瘤抑制因子，也是 Wnt/β-catenin 信号通路的关键负调节因子。 Axin 周转由坦科聚合酶 (TNKS) 催化的聚 ADP 核糖基化控制，这需要 Axin 与 TNKS 直接相互作用。因此，这种相互作用是治疗癌症、脑损伤和其他涉及 β-连环蛋白的疾病的有吸引力的药物靶点。在这里，我们报告了小鼠 TNKS1 片段的晶体结构，其中包含锚蛋白重复簇 2 和 3 (ARC2-3)，与小鼠 Axin1 的 TNKS 结合结构域形成复合物。令人惊讶的是，我们发现 Axin 包含两个离散的 TNKS 结合片段，这两个片段同时与 ARC2-3 同二聚体中的两个 ARC2 结构域结合。我们的晶体结构表明，在 Axin 的每个 TNKS 结合片段中，都有一个保守的甘氨酸残基，位于由 TNKS 表面上两个平行的酪氨酸侧链形成的狭窄“门”的底部。这种甘氨酸选择门对于 TNKS-Axin 相互作用至关重要，因为 TNKS 门形成残基的突变，或两个 Axin 片段中任一甘氨酸残基的突变，完全废除了相应 Axin 片段与 TNKS 的结合。 Axin 与 TNKS 的二价结合是 Axin 周转所必需的，因为 Axin 中任一门结合甘氨酸残基的突变都会导致 Axin 在细胞中稳定。此外，我们的分析还揭示了 TNKS 底物招募的结构基础，并揭示了 TNKS 的整体结构，这有助于开发 Wnt/β-catenin 信号传导的特异性抑制剂。
Axin is a tumor suppressor and a key negative regulator of the Wnt/beta-catenin signaling pathway. Axin turnover is controlled by its poly-ADP-ribosylation catalyzed by tankyrase (TNKS), which requires the direct interaction of Axin with TNKS. This interaction is thus an attractive drug target for treating cancers, brain injuries, and other diseases where beta-catenin is involved. Here we report the crystal structure of a mouse TNKS1 fragment containing ankyrin-repeat clusters 2 and 3 (ARC2-3) in a complex with the TNKS-binding domain of mouse Axin1. Surprisingly, we found that Axin contains two discrete TNKS-binding segments, both of which bind simultaneously to the two ARC2 domains in the ARC2-3 homodimer. Our crystal structure shows that in each TNKS-binding segment of Axin there is a conserved glycine residue that lies in the bottom of a narrow "gate" formed by two parallel tyrosine side chains on the TNKS surface. This glycine-selection gate is crucial for TNKS-Axin interactions, as mutation of the TNKS gate-forming residues, or mutation of either glycine residue in the two Axin segments, completely abolishes the binding of the corresponding Axin segment to TNKS. The bivalent binding of Axin to TNKS is required for Axin turnover, since mutations in either gate-binding glycine residue in Axin lead to Axin stabilization in the cell. In addition, our analyses also reveal the structural basis for TNKS substrate recruitment, and shed light on the overall structure of TNKS that should help in developing specific inhibitors of Wnt/beta-catenin signaling.