Hedgehog signaling plays a crucial role in embryogenesis and adult tissue homeostasis, and mutations of its key components such as Suppressor of fused (Sufu) are closely associated with human diseases. The Ser/Thr kinase Fused (Fu) promotes Hedgehog signaling by phosphorylating the Cubitus interruptus (Ci)/Glioma-associated oncogene homologue (Gli) family of transcription factors. Sufu associates with both Fu and Ci/Gli, but the recognition mechanism between Sufu and Fu remains obscure. Here, our structure of the N-terminal domain (NTD) of Drosophila Sufu (dSufu) in complex with the Sufu-binding site (SBS) of Fu reveals that both main-chain β sheet formation and side-chain hydrophobic interactions contribute to the recognition between Sufu and Fu, and point mutations of highly conserved interface residues eliminated their association. Structural comparison suggests that Fu and Ci/Gli bind on opposite sides of dSufu-NTD, allowing the formation of a Fu-dSufu-Ci ternary complex which facilitates the phosphorylation of Ci/Gli by Fu. Hence, our results provide insights into the Sufu-Fu recognition mechanism.

Hedgehog 信号在胚胎发生和成体组织稳态中起着至关重要的作用，其关键成分如融合抑制因子（Sufu）的突变与人类疾病密切相关。Ser/Thr 激酶融合 (Fu) 通过磷酸化肘节中断 (Ci)/胶质瘤相关癌基因同源物 (Gli) 转录因子家族来促进 Hedgehog 信号传导。Sufu 与 Fu 和 Ci/Gli 都有关联，但 Sufu 和 Fu 之间的识别机制仍然模糊不清。在这里，我们的果蝇N 端结构域 (NTD) 的结构Sufu (dSufu) 与 Fu 的 Sufu 结合位点 (SBS) 的复合物表明，主链 β 折叠形成和侧链疏水相互作用都有助于 Sufu 和 Fu 之间的识别，并且消除了高度保守的界面残基的点突变他们的协会。结构比较表明 Fu 和 Ci/Gli 结合在 dSufu-NTD 的相对两侧，从而形成 Fu-dSufu-Ci 三元复合物，促进 Fu 对 Ci/Gli 的磷酸化。因此，我们的结果提供了对 Sufu-Fu 识别机制的见解。