title: Insights into the molecular basis for fibroblast growth factor receptor autoinhibition and ligand-binding promiscuity.
abstract: 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.
authors.affiliation: Departments of Pharmacology and Microbiology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Shaun K
authors.initials: SK
authors.lastname: Olsen
authors.forename: Omar A
authors.initials: OA
authors.lastname: Ibrahimi
authors.forename: Angela
authors.initials: A
authors.lastname: Raucci
authors.forename: Fuming
authors.initials: F
authors.lastname: Zhang
authors.forename: Anna V
authors.initials: AV
authors.lastname: Eliseenkova
authors.forename: Avner
authors.initials: A
authors.lastname: Yayon
authors.forename: Claudio
authors.initials: C
authors.lastname: Basilico
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Linhardt
authors.forename: Joseph
authors.initials: J
authors.lastname: Schlessinger
authors.forename: Moosa
authors.initials: M
authors.lastname: Mohammadi
mesh_terms: 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
chemical_list: D008024:Ligands; D017468:Receptors, Fibroblast Growth Factor; D016220:Fibroblast Growth Factor 1; D006493:Heparin