Insights into the molecular basis for fibroblast growth factor receptor autoinhibition and ligand-binding promiscuity.
The prototypical fibroblast growth factor receptor (FGFR) extracellular domain consists of three Ig domains (D1-D3) of which the two membrane-proximal D2 and D3 domains and the interconnecting D2-D3 linker bear the determinants of ligand binding and specificity. In contrast, D1 and the D1-D2 linker are thought to play autoinhibitory roles in FGFR regulation. Here, we report the crystal structure of the three-Ig form of FGFR3c in complex with FGF1, an FGF that binds promiscuously to each of the seven principal FGFRs. In this structure, D1 and the D1-D2 linker are completely disordered, demonstrating that these regions are dispensable for FGF binding. Real-time binding experiments using surface plasmon resonance show that relative to two-Ig form, the three-Ig form of FGFR3c exhibits lower affinity for both FGF1 and heparin. Importantly, we demonstrate that this autoinhibition is mediated by intramolecular interactions of D1 and the D1-D2 linker with the minimal FGF and heparin-binding D2-D3 region. As in the FGF1-FGFR2c structure, but not the FGF1-FGFR1c structure, the alternatively spliced betaC'-betaE loop is ordered and interacts with FGF1 in the FGF1-FGFR3c structure. However, in contrast to the FGF1-FGFR2c structure in which the betaC'-betaE loop interacts with the beta-trefoil core region of FGF1, in the FGF1-FGFR3c structure, this loop interacts extensively with the N-terminal region of FGF1, underscoring the importance of the FGF1 N terminus in conferring receptor-binding affinity and promiscuity. Importantly, comparison of the three FGF1-FGFR structures shows that the flexibility of the betaC'-betaE loop is a major determinant of ligand-binding specificity and promiscuity.
Olsen
Shaun K
SK
Departments of Pharmacology and Microbiology, New York University School of Medicine, New York, NY 10016, USA.
Ibrahimi
Omar A
OA
Raucci
Angela
A
Zhang
Fuming
F
Eliseenkova
Anna V
AV
Yayon
Avner
A
Basilico
Claudio
C
Linhardt
Robert J
RJ
Schlessinger
Joseph
J
Mohammadi
Moosa
M
D000595:Amino Acid Sequence; D016220:Fibroblast Growth Factor 1 / Q000378:metabolism; D006493:Heparin / Q000378:metabolism; D008024:Ligands; D008969:Molecular Sequence Data; D017468:Receptors, Fibroblast Growth Factor / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D020349:Surface Plasmon Resonance
D008024:Ligands; D017468:Receptors, Fibroblast Growth Factor; D016220:Fibroblast Growth Factor 1; D006493:Heparin