Conformation of glutathione adduct and oxidized forms of platelet-derived growth factor

The conformational properties of several platelet‐derived growth factors (PDGFs) were characterized by circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), gel filtration and sedimentation equilibrium. Three different forms of disulfide linked dimer, PDGF‐AA, PDGF‐AB, and PDGF‐BB, showed similar far UV CD spectra with evidence for slight p‐structure, but little evidence of other regular secondary structures. These spectra were, however, different from the far UV CD spectra of the glutathione adducts of PDGF‐A and B, suggesting that the latter two proteins adopt different conformations in the absence of intra‐ or inter‐molecular disulfide bonds. FTIR studies confirmed this by showing that the glutathione adducts of the PDGF‐B protein have a significantly lower amount of regular secondary structures than PDGF‐BB. Additionally, the increased bandwidths of the amide I components of the FTIR spectrum of the glutathione adduct indicates a more flexible structure relative to the dimeric form. Sedimentation equilibrium analysis showed that PDGF‐BB is primarily a dimer and that the glutathione form is primarily a monomer. Thus, it was concluded that the glutathione derivative has little affinity to form non‐covalent dimers in neutral solution.