Structure of fibroblast growth factor 9 shows a symmetric dimer with unique receptor- and heparin-binding interfaces

Abstract

Fibroblast growth factors (FGFs) constitute a family of at least 20 structurally related heparin-binding polypeptides active in regulating cell growth, survival, differentiation and migration. FGF9, originally discovered as a glia-activating factor, shares 30% sequence identity with other FGFs and has a unique spectrum of target-cell speci®city. FGF9 crystallized in the tetragonal space group I4 1 , with unit-cell parameters a = b = 151.9, c = 117.2 A Ê . The structure of the glycosylated protein has been re®ned to an R value of 21.0% with R free = 24.8%) at 2.6 A Ê resolution. The four molecules in the asymmetric unit are arranged in two non-crystallographic dimers, with the dimer interface composed partly of residues from N-and C-terminal extensions from the FGF core structure. Most of the receptor-binding residues identi®ed in FGF1± and FGF2±receptor complexes are buried in the dimer interface, with the 8± 9 loop stabilized in a particular conformation by an intramolecular hydrogen-bonding network. The potential heparin-binding sites are in a pattern distinct from FGF1 and FGF2. The carbohydrate moiety attached at Asn79 has no structural in¯uence.

Experimental support for the foldability–function tradeoff hypothesis: Segregation of the folding nucleus and functional regions in fibroblast growth factor‐1

“…These data are consistent with a polarized transition state. [30][31][32][33] threefold symmetric tertiary structure) of critical folding and functional elements in FGF-1, thus supporting the foldability-function tradeoff hypothesis.…”

“…[37][38][39] Furthermore, the competent signal transduction complex of FGF-1 involves a ternary interaction between FGF-1, FGF receptor, and HSPG. [30][31][32][33] The addition of soluble heparin to FGF-1 confers resistance to thermal denaturation, chemical denaturation, and proteolysis, 28,40,41 and inclusion of heparin in the formulation of FGF-1 greatly improves its potency, stability, storage, and reconstitution properties. 28 Thus, heparin binding represents a key functionality that regulates the tissue distribution, pharmacokinetics, and receptor signaling of FGF-1.…”

Symmetric Primary and Tertiary Structure Mutations within a Symmetric Superfold: A Solution, not a Constraint, to Achieve a Foldable Polypeptide

“…Structural and biochemical studies of FGFs identify a key role for heparin in forming a functional signal transduction complex of FGF with its receptor (FGFR). 21,[35][36][37][38][39][40] Thus, it came as a surprise to find that the SYM6DD mutant exhibits an EC 50 value that is almost two orders of magnitude more potent in comparison to WT * FGF-1 (Figure 3). A comparison with other FGF-1 mutants involving only a single loop deletion indicates that this increase in potency is associated with the D120-122 mutation.…”

Differential Interactions of FGFs with Heparan Sulfate Control Gradient Formation and Branching Morphogenesis

“…Structure-based sequence alignment of members of other FGF subfamilies including FGF4/6, FGF8/17/18, and FGF9/16/20 reveals primary amino acid differences in the heparin-binding region, which suggest the existence of differences in HS-binding affinities among members of these subfamilies as well (1, 48–50). These differences may contribute to the divergent biology of these FGFs in vivo through conferring distinct diffusion gradient potentials.…”