Abstract：
SSR128129E (SSR) is a unique small-molecule inhibitor of fibroblast growth factor receptors (FGFRs). SSR is a high-affinity allosteric binder that selectively blocks one of the two major FGFR-mediated pathways. The mechanisms of SSR activity were studied previously in much detail, allowing the identification of its binding site, located in the hydrophobic groove of the receptor D3 domain. The binding site overlaps with the position of an N-terminal helix, an element exclusive for the FGF8b growth factor, which could potentially convert SSR from an allosteric inhibitor into an orthosteric blocker for the particular FGFR/FGF8b system. In this regard, we report here on the structural and functional investigation of FGF8b/FGFR3c system and the effects imposed on it by SSR. We show that SSR is equally or more potent in inhibiting FGF8b-induced FGFR signaling compared to FGF2-induced activation. On the other hand, when studied in the context of separate extracellular domains of FGFR3c in solution with NMR spectroscopy, SSR is unable to displace the N-terminal helix of FGF8b from its binding site on FGFR3c and behaves as a weak orthosteric inhibitor. The substantial inconsistency between the results obtained with cell culture and for the individual water-soluble subdomains of the FGFR proteins points to the important role played by the cell membrane.
摘要：
SSR128129E（SSR）是一种独特的成纤维细胞生长因子受体（FGFR）小分子抑制剂。SSR是高亲和力变构结合剂,其选择性阻断两种主要FGFR介导的途径之一。以前对SSR活性的机制进行了详细的研究，允许鉴定其结合位点，位于受体D3域的疏水沟。结合位点与N端螺旋的位置重叠，FGF8b生长因子的专有元素，对于特定的FGFR/FGF8b系统，这可能会将SSR从变构抑制剂转化为正构阻断剂。在这方面,我们在此报告FGF8b/FGFR3c系统的结构和功能研究以及SSR对其的影响。我们表明，与FGF2诱导的激活相比，SSR在抑制FGF8b诱导的FGFR信号传导方面同等或更有效。另一方面,当在NMR光谱溶液中FGFR3c的单独胞外域的背景下进行研究时，SSR不能将FGF8b的N-末端螺旋从其在FGFR3c上的结合位点置换,并且表现为弱的正构抑制剂。用细胞培养获得的结果与FGFR蛋白的单个水溶性亚结构域之间的实质性不一致表明细胞膜发挥了重要作用。
