K. M. Kathir1, A. I. Arunkumar1, T. K. S. Kumar1, S. Srisailam1, Han-Min Wang1, Ya-hui Chi1, Gu-Gang Chang2 and Chin Yu1*
1. Department of Chemistry, National Tsing Hua Universisty, Hsinchu, Taiwan.
2. Department of Biochemistry, National Defense Medical Center, Taipei, Taiwan.
Oligomerization of fibroblast growth factors (FGFs) induced on binding to heparin or heparan sulfate proteoglycan is considered to be crucial for receptor activation and initiation of biological responses. To gain insight(s) into the mechanism of activation of the receptor by FGFs, in the present study we investigate the effect(s) of interaction of a heparin analog, sucrose octasulfate (SOS), on the structure, stability and biological activities of a recombinant acidic fibroblast growth factor from Notophthalmus viridescens (nFGF-1). SOS is found to bind to nFGF-1 and significantly increase the thermodynamic stability of the protein. Using a variety of techniques such as size-exclusion chromotagraphy, circular dichroism, fluorescence, sedimentation velocity and multidimensional NMR spectroscopy, it is shown that binding of SOS to nFGF-1 retains the protein in its monomeric state. However, nFGF-1 complexed to SOS shows significant mitogenic and angiogenic activities. 15N and 1H chemical shift perturbation and the intermolecular NOEs between SOS and nFGF-1 reveals that the ligand binds to the dense, positively charged cluster located in the groove enclosed by b-strands 10 and 11. In addition, molecular modeling based on the NOEs observed for the SOS - nFGF-1 complex, indicates that SOS and heparin share a common binding site on the protein. To our knowledge, the present study is the first report wherein it is demonstrated that heparin-induced oligomerization of FGF is not mandatory for its cell proliferation activity.