The SRP54 GTPase is a key component of co-translational protein targeting by the signal recognition particle (SRP). Point mutations in SRP54 have been recently shown to lead to a form of severe congenital neutropenia displaying symptoms overlapping with those of Shwachman-Diamond syndrome. The phenotype includes severe neutropenia, exocrine pancreatic deficiency, and neurodevelopmental as well as skeletal disorders. Using a combination of X-ray crystallography, hydrogen-deuterium exchange coupled to mass spectrometry and complementary biochemical and biophysical methods, we reveal extensive structural defects in three disease-causing SRP54 variants resulting in critical protein destabilization. GTP binding is mostly abolished as a consequence of an altered GTPase core. The mutations located in conserved sequence fingerprints of SRP54 eliminate targeting complex formation with the SRP receptor as demonstrated in yeast and human cells. These specific defects critically influence the entire SRP pathway, thereby causing this life-threatening disease.

SRP54 GTPase 是信号识别粒子 (SRP) 共翻译蛋白靶向的关键组成部分。最近显示 SRP54 中的点突变会导致一种严重的先天性中性粒细胞减少症，其症状与 Shwachman-Diamond 综合征的症状重叠。表型包括严重的中性粒细胞减少症、胰腺外分泌缺陷以及神经发育和骨骼疾病。使用 X 射线晶体学、氢-氘交换与质谱法以及互补的生化和生物物理方法相结合，我们揭示了导致关键蛋白质不稳定的三种致病 SRP54 变体的广泛结构缺陷。由于 GTPase 核心的改变，GTP 结合大多被废除。位于 SRP54 保守序列指纹中的突变消除了与 SRP 受体的靶向复合物形成，如在酵母和人类细胞中所证明的。这些特定缺陷严重影响整个 SRP 通路，从而导致这种危及生命的疾病。