Platelet-derived growth factor (PDGF)-C, a PDGF family member with a vascular endothelial growth factor-like structure

Platelet-derived growth factor (PDGF)-C is a novel member of the PDGF family that binds to PDGF alphaalpha and alphabeta receptors. The growth factor domain of PDGF-C (GFD-PDGF-C) was expressed in high yields in Escherichia coli and was purified and refolded from inclusion bodies obtaining a biologically active growth factor with dimeric structure. The GFD-PDGF-C contains 12 cysteine residues, and Ellman assay analysis indicates that it contains three intramonomeric disulfide bonds, which is in accordance with GFD-PDGF-C being a member of the cystine knot superfamily of growth factors. The recombinant GFD-PDGF-C was characterized by CD, fluorescence, NMR, and infrared spectroscopy. Together, our data indicate that GFD-PDGF-C is a highly thermostable protein that contains mostly beta-sheet secondary structure and some (6%) alpha-helix structure. The structural model of PDGF-C, obtained by homology-based molecular modeling using the structural representatives of this family of growth factors, shows that GFD-PDGF-C has a higher structural homology to the vascular endothelial growth factor than to PDGF-B. The modeled structure can give further insights into the function and specificity of this molecule.