Interaction of ATP with fibroblast growth factor 2: biochemical characterization and consequence for growth factor stability

Here we determined the dissociation constant of ATP on FGF2 by equilibrium microdialysis (KD: 59.8 μM) and analyzed the impact of this binding on secondary structure by CD-spectroscopy. ATP-binding to FGF2 significantly changed the secondary structure of this growth factor with a shift to random coil structure elements. We also analyzed the influence of this binding on the stability of FGF2 in aqueous solution over a period of 2 h. While the amount of untreated FGF2 is reduced drastically over this period of time, ATP-binding reduces the degradation considerably.Taken together, our data suggest an important role of ATP in FGF2-stabilization beside the well known-role of heparin and heparan sulphate.Some groups of protein families are known to bind ATP, for example kinases and ABC transporters. Both protein families possess a conserved ATP-binding domain called P-loop (formerly Walker motif A: GXXG(X)XGKT(X); [1,2]. However, ATP-binding which is not based on a specific ATP-binding domain, is described for many other proteins like lactoferrin [3], bovine serum albumin [4] or gelsolin [5]. Recently, the interaction of ATP with growth factors was discovered [6]. The physiological role of this ATP-binding to growth factors remained unclear. However, binding of ATP to NGF and FGF2 seems to be essential for their neuroprotectivity as demonstrated with hippocampal neuronal cells [7,8]. The heparin binding domain (HBD) of both growth factors is important for ATP-binding [7,9] although crystallographic data of the growth factor/ATP-complexes are not yet available.Complex formation of ATP with NGF and FGF2 is probably based on ionic interaction of the negatively charged phosphate residues of ATP with positively charged arginine and lysine residues located in the HBD of NGF and FGF2, respectively. This is similar to the interaction of sulphate residues of heparin or heparan sulphate-proteoglycans (HSPGs) with heparin-binding growth factors like fibroblast growth factors, VEGF,