Structural basis for interaction of FGF-1, FGF-2, and FGF-7 with different heparan sulfate motifs.
Stromal cell-derived FGF-7 binds and activates only the resident FGFR2IIIb in epithelial cells while FGF-1 and FGF-2 exhibit a broader interaction with multiple isoforms of FGFR. Here we report the structure of FGF-7 that has been solved to 3.1 A resolution by molecular replacement with the structure of a dual function chimera of FGF-7 and FGF-1 (FGF-7/1) which was resolved to 2.3 A. Comparison of the FGF-7 structure to that of FGF-1 and FGF-2 revealed the strongly conserved Calpha backbone among the three FGF polypeptides and the surface hydrophobic patch that forms the primary receptor-binding domain. In contrast, a decrease and dispersion of the positive surface charge density characterized the heparin-binding domain of FGF-7 defined by homology to that of FGF-1 and FGF-2 in complexes with heparin. A simple heparin hexasaccharide that cocrystallized with FGF-1 and FGF-2 and protected both against protease in solution failed to exhibit the same properties with FGF-7. In contrast to FGF-1 and FGF-2, protection of FGF-7 was enhanced by heparin oligosaccharides of increased length with those exhibiting a 3-O-sulfate being the most effective. Protection of FGF-7 required interaction with specifically the fraction of crude heparin retained on antithrombin affinity columns. Conversely, heparin enriched by affinity for immobilized FGF-7 exhibited anti-factor Xa activity similar to that purified on an antithrombin affinity matrix. In contrast, an FGF-1 affinity matrix enriched the fraction of crude heparin with low anti-factor Xa activity. The results provide a structural basis to suggest that the unique FGF-7 heparin-binding (HB) domain underlies a specific restriction in respect to composition and length of the heparan sulfate motif that may impact specificity of localization, stability, and trafficking of FGF-7 in the microenvironment, and formation and activation of the FGFR2IIIb kinase signaling complex in epithelial cells.
Ye
S
S
Department of Biochemistry, Baylor College of Medicine, One Baylor Plaza, Houston, Texas, 77030, USA.
Luo
Y
Y
Lu
W
W
Jones
R B
RB
Linhardt
R J
RJ
Capila
I
I
Toida
T
T
Kan
M
M
Pelletier
H
H
McKeehan
W L
WL
D000595:Amino Acid Sequence; D003460:Crystallization; D015951:Factor Xa / Q000276:immunology / Q000378:metabolism; D016220:Fibroblast Growth Factor 1 / Q000737:chemistry / Q000378:metabolism*; D016222:Fibroblast Growth Factor 2 / Q000737:chemistry / Q000378:metabolism*; D051523:Fibroblast Growth Factor 7; D005346:Fibroblast Growth Factors / Q000737:chemistry / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006497:Heparan Sulfate / Q000378:metabolism*; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
D015951:Factor Xa; D016220:Fibroblast Growth Factor 1; D016222:Fibroblast Growth Factor 2; D051523:Fibroblast Growth Factor 7; D005346:Fibroblast Growth Factors; D006493:Heparin; D006497:Heparan Sulfate; D011994:Recombinant Proteins