Wang F, Lu W, McKeehan K, Mohamedali K, Gabriel J L, Kan M, McKeehan W L
Center for Cancer Biology and Nutrition, Institute of Biosciences and Technology, Department of Biochemistry and Biophysics, Texas A&M University, Houston 77030, USA.
Biochemistry. 1999 Jan 5;38(1):160-71. doi: 10.1021/bi981758m.
The assembly and activation of oligomeric complexes of FGF, the transmembrane receptor kinase (FGFR), and heparan sulfate transmit intracellular signals regulating growth and function of cells. An understanding of the structural relationships between the three subunits and their redundancy and specificity is essential for understanding the ubiquitous FGF signaling system in health and disease. Previously, we reported that a primary heparin or heparan sulfate binding site resides in a distinct sequence in immunoglobulin (Ig)-like module II of the three modules of FGFR. Here we report that in the absence of flanking sequences, isolated Ig module II of FGFR1 supports the binding of FGF-1, FGF-2, and FGF-7 in respective order of affinity. None of the three FGFs detectably bind Ig module I or the IIIb and IIIc splice variants of Ig module III in the absence of flanking sequences. Ig module I and the C-terminus of Ig module III are dispensable for high-affinity binding of FGF-1, FGF-2, and FGF-7. Alterations in highly conserved Ig module II in the heparin binding domain and substitution of individual sequence domains spanning the entire sequence of Ig module II with those from Ig module I obliterated FGF binding. Addition of a specific number of FGFR sequences to the C-terminus of Ig module II resulted in a gain in affinity for FGF-7. Several site-specific alterations in the C-terminus of full-length FGFR1IIIc, an isoform that otherwise absolutely rejects FGF-7, resulted in gain of FGF-7 binding. These results suggest that a complex of Ig module II and heparan sulfate is the base common active core of the FGFR ectodomain and that flanking structural domains modify FGF affinity and determine specificity.
成纤维细胞生长因子（FGF）、跨膜受体激酶（FGFR）和硫酸乙酰肝素的寡聚复合物的组装与激活可传递调节细胞生长和功能的细胞内信号。了解这三个亚基之间的结构关系及其冗余性和特异性对于理解健康和疾病中普遍存在的FGF信号系统至关重要。此前，我们报道主要的肝素或硫酸乙酰肝素结合位点位于FGFR三个模块中免疫球蛋白（Ig）样模块II的一个独特序列中。在此我们报道，在没有侧翼序列的情况下，分离的FGFR1的Ig模块II按亲和力顺序支持FGF-1、FGF-2和FGF-7的结合。在没有侧翼序列的情况下，这三种FGF均未检测到与Ig模块I或Ig模块III的IIIb和IIIc剪接变体结合。Ig模块I和Ig模块III的C末端对于FGF-1、FGF-2和FGF-7的高亲和力结合是可有可无的。肝素结合域中高度保守的Ig模块II的改变以及用Ig模块I的序列替换跨越Ig模块II整个序列的单个序列域消除了FGF结合。在Ig模块II的C末端添加特定数量的FGFR序列导致对FGF-7的亲和力增加。全长FGFR1IIIc（一种否则绝对排斥FGF-7的异构体）的C末端的几个位点特异性改变导致FGF-7结合增加。这些结果表明，Ig模块II和硫酸乙酰肝素的复合物是FGFR胞外域共同的基础活性核心，并且侧翼结构域修饰FGF亲和力并决定特异性。
