| Summary: | Vascular endothelial growth factor-A (VEGF-A), a secreted homodimeric glycoprotein, is a critical regulator of angiogenesis in normal and pathological states. The binding of heparin (HE) to VEGF<sub>165</sub> (the major form of VEGF-A) modulates the angiogenesis-related cascade, but the mechanism of the observed changes at the structural level is still insufficiently explored. In the present study, we examined the effect of HE on the structural and physicochemical properties of recombinant human VEGF<sub>165</sub> (rhVEGF<sub>165</sub>). The HE binding results in an increase of hydrophobic surface exposure in rhVEGF<sub>165</sub> without changes in its secondary structure. Differential scanning calorimetry measurements for intact and HE-bound rhVEGF<sub>165</sub> reveals the absence of any pronounced thermally induced transitions in the protein in the temperature range from 20 to 100 °C. The apolar area increase during the heparin binding explains the pronounced HE-induced oligomerization/aggregation of rhVEGF<sub>165</sub>, as studied by chemical glutaraldehyde cross-linking and dynamic light scattering. Molecular modeling and docking techniques were used to model the full structure of dimeric VEGF<sub>165</sub> and to reveal putative molecular mechanisms underlying the function of the VEGF<sub>165</sub>/HE system. In general, the results obtained can be a basis for explaining the modulating effect of HE on the biological activity of VEGF-A.
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