Fungal transcription factor Upc2 senses ergosterol levels and regulates sterol biosynthesis and uptake. Constitutive activation of Upc2 causes azole resistance in Candida species. We determined the structure of ergosterol-bound Upc2, revealing the ligand specificity and transcriptional regulation. Ergosterol binding involves conformational changes of the ligand-binding domain, creating a shape-complementary hydrophobic pocket. The conserved helix α12 and glycine-rich loop are critical for sterol recognition by forming the pocket wall. The mutations of the glycine-rich loop inhibit ligand binding by steric clashes and constitutively activate Upc2. The translocation of Upc2 is regulated by Hsp90 chaperone in a sterol-dependent manner. Ergosterol-bound Upc2 associates with Hsp90 using the C-terminal tail, which retains the inactive Upc2 in the cytosol. Ergosterol dissociation induces a conformational change of the C-terminal tail, releasing Upc2 from Hsp90 for nuclear transport by importin α. The understanding of the regulatory mechanism provides an antifungal target for the treatment of azole-resistant Candida infections.

真菌转录因子 Upc2 感知麦角固醇水平并调节固醇生物合成和摄取。Upc2 的组成型激活导致念珠菌的唑类耐药性物种。我们确定了麦角甾醇结合的 Upc2 的结构，揭示了配体特异性和转录调控。麦角甾醇结合涉及配体结合域的构象变化，从而产生形状互补的疏水口袋。保守的螺旋 α12 和富含甘氨酸的环通过形成袋壁对甾醇识别至关重要。富含甘氨酸环的突变通过空间碰撞抑制配体结合并组成型激活 Upc2。Upc2 的易位受 Hsp90 分子伴侣以甾醇依赖性方式调节。麦角甾醇结合的 Upc2 使用 C 末端尾巴与 Hsp90 结合，它在胞质溶胶中保留了无活性的 Upc2。麦角固醇解离诱导 C 末端尾部的构象变化，从 Hsp90 释放 Upc2 以通过输入蛋白 α 进行核转运。念珠菌感染。