PDF(Pubmed)
Abstract：
α-Klotho (KLA) is a type-1 membranous protein that can associate with fibroblast growth factor receptor (FGFR) to form co-receptor for FGF23. The ectodomain of unassociated KLA is shed as soluble KLA (sKLA) to exert FGFR/FGF23-independent pleiotropic functions. The previously determined X-ray crystal structure of the extracellular region of sKLA in complex with FGF23 and FGFR1c suggests that sKLA functions solely as an on-demand coreceptor for FGF23. To understand the FGFR/FGF23-independent pleiotropic functions of sKLA, we investigated biophysical properties and structure of apo-sKLA. Mass photometry revealed that sKLA can form a stable structure with FGFR and/or FGF23 as well as sKLA dimer in solution. Single particle cryogenic electron microscopy (cryo-EM) supported the dimeric structure of sKLA. Cryo-EM further revealed a 3.3Å resolution structure of apo-sKLA that overlays well with its counterpart in the ternary complex with several distinct features. Compared to the ternary complex, the KL2 domain of apo-sKLA is more flexible. 3D variability analysis revealed that apo-sKLA adopts conformations with different KL1-KL2 interdomain bending and rotational angles. The potential multiple forms and shapes of sKLA support its role as FGFR-independent hormone with pleiotropic functions. A comprehensive understanding of the sKLA conformational landscape will provide the foundation for developing klotho-related therapies for diseases.
摘要：
α-Klotho（KLA）是1型膜蛋白，可与成纤维细胞生长因子受体（FGFR）结合形成FGF23的共受体。未结合的KLA的胞外域作为可溶性KLA(sKLA)脱落以发挥FGFR/FGF23非依赖性多效性功能。先前确定的与FGF23和FGFR1c复合的sKLA胞外区的X射线晶体结构表明，sKLA仅充当FGF23的按需共受体。为了了解sKLA的FGFR/FGF23独立的多效性功能，我们研究了apo-sKLA的生物物理特性和结构。质量光度法显示sKLA可以与FGFR和/或FGF23以及sKLA二聚体在溶液中形成稳定的结构。单粒子低温电子显微镜（cryo-EM）支持sKLA的二聚体结构。Cryo-EM进一步揭示了apo-sKLA的3.3bias分辨率结构，该结构与三元复合物中的对应物很好地重叠，具有几个明显的特征。与三元络合物相比，apo-sKLA的KL2域更灵活。3D变异性分析表明，apo-sKLA采用具有不同KL1-KL2域间弯曲和旋转角度的构象。sKLA的潜在多种形式和形状支持其作为具有多效功能的非FGFR依赖性激素的作用。对sKLA构象景观的全面了解将为开发与klotho相关的疾病疗法奠定基础。
