Thermodynamic and structural description of allosterically regulated VEGFR-2 dimerization.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Vascular Endothelial Growth Factors (VEGFs) are key regulators of angiogenesis and lymphangiogenesis.
• VEGFs activate three receptor tyrosine kinases: VEGFR-1, VEGFR-2, and VEGFR-3.
• The extracellular domain (ECD) of VEGFR-2 comprises 7 Ig-homology domains; domains 2 and 3 (D23) bind ligands, while domains 4-7 (D4-7) have an undefined role.

Purpose of the Study:

• To investigate the function of VEGFR-2 domains D4-7 in VEGF binding and receptor activation.
• To elucidate the structural and energetic basis of VEGF-VEGFR-2 interactions.

Main Methods:

• Isothermal titration calorimetry (ITC) to determine binding thermodynamics.
• Small-angle scattering (SAS) to model complex structures.
• Crystal structure determination of VEGF-A/VEGF-E and VEGFR-2 D23 complexes.

Main Results:

• VEGF binding to VEGFR-2 ECD is entropically driven with an enthalpic penalty, less favorable than binding to D23 alone.
• SAS modeling suggests homotypic interactions within D4-7 of the VEGFR-2 ECD.
• Crystal structures reveal conserved binding interfaces but variations in D23 conformation.

Conclusions:

• Energetically unfavorable homotypic interactions in D4-7 may facilitate receptor monomer re-orientation.
• This mechanism potentially prevents ligand-independent VEGFR-2 activation, crucial for maintaining vascular homeostasis.
• Understanding these interactions is vital for controlling angiogenesis and lymphangiogenesis.