Aspergillus fumigatus is a human opportunistic pathogen showing emerging resistance against a limited repertoire of antifungal agents available. The GTPase Rho1 has been identified as an important regulator of the cell wall integrity signaling pathway that regulates the composition of the cell wall, a structure that is unique to fungi and serves as a target for antifungal compounds. Rom2, the guanine nucleotide exchange factor to Rho1, contains a C-terminal citron homology (CNH) domain of unknown function that is found in many other eukaryotic genes. Here, we show that the Rom2 CNH domain interacts directly with Rho1 to modulate β-glucan and chitin synthesis. We report the structure of the Rom2 CNH domain, revealing that it adopts a seven-bladed β-propeller fold containing three unusual loops. A model of the Rho1–Rom2 CNH complex suggests that the Rom2 CNH domain interacts with the Rho1 Switch II motif. This work uncovers the role of the Rom2 CNH domain as a scaffold for Rho1 signaling in fungal cell wall biosynthesis.

烟曲霉是一种人类机会性病原体，显示出对有限的可用抗真菌剂的耐药性。GTPase Rho1 已被确定为细胞壁完整性信号通路的重要调节因子，它调节细胞壁的组成，这是一种真菌独有的结构，可作为抗真菌化合物的靶标。Rom2 是 Rho1 的鸟嘌呤核苷酸交换因子，它包含在许多其他真核基因中发现的未知功能的 C 末端香橼同源 (CNH) 域。在这里，我们表明 Rom2 CNH 结构域直接与 Rho1 相互作用以调节 β-葡聚糖和几丁质合成。我们报告了 Rom2 CNH 结构域的结构，揭示了它采用包含三个不寻常环的七叶 β-螺旋桨折叠。Rho1-Rom2 CNH 复合体的模型表明 Rom2 CNH 结构域与 Rho1 Switch II 基序相互作用。这项工作揭示了 Rom2 CNH 结构域作为 Rho1 信号传导在真菌细胞壁生物合成中的支架的作用。