Effect of polyanions on the structure and stability of repifermin (keratinocyte growth factor-2)

The interaction of several of the fibroblast growth factors (FGFs) with polyanions is thought to be of physiological significance and has been exploited to create more stable pharmaceutical formulations of FGF-1 and -2. The extent of such phenomena throughout the 23-member FGF family is, however, unknown. In these studies, we examine the effect of several polyanions on the structure and stability of keratinocyte growth factor 2 (KGF-2, FGF-10), a candidate for use as a wound-healing agent. Employing a variety of methods sensitive to the protein's structure including circular dichroism (CD), intrinsic fluorescence, derivative near-UV absorption spectroscopy, bis-ANS (4,4'-dianilino-1,1'-binaphthyl-5,5-disulfonic acid) fluorescence, differential scanning calorimetry (DSC), and dynamic light scattering (DLS), we find that a variety of polyanions (e.g., heparin, sucrose octasulfate (SOS), and inositol hexaphosphate (IHP)) stabilize KGF-2 by increasing the thermal-unfolding temperature by approximately 9-15 degrees C. Negatively charged liposomes produce a similar effect, arguing for relatively nonspecific interactions of polyanions with KGF-2. Unlike some other FGFs, no evidence for the presence of a molten globule state is found during thermal perturbation of this growth factor. The generality of this polyanion/protein interaction is discussed as well as its potential role in various cellular events such as protein folding and transport.