Structure-fluctuation-function relationships of seven pro-angiogenic isoforms of VEGFA, important mediators of tumorigenesis.

Vascular endothelial growth factor A (VEGFA) has different biological activities and plays a central role in tumor proliferation, angiogenesis and metastasis. Different VEGFA isoforms are generated by alternative splice site selection of exons 6, 7 and 8. In this paper, we analyzed the physical and chemical properties of the VEGFA exon 6 sequence, and modeled the three-dimensional structures of the regions corresponding to exons 6, 7 and 8 of six different pro-angiogenic isoforms of VEGFA in comparison to the experimental structure of VEGFA_165 by a combined approach of fold recognition and comparative modeling strategies and molecular dynamics simulations. Our results showed that i) exon 6 is a very flexible polycation with high disordered propensity, features well conserved in all mammals, ii) the structures of all the isoforms are stabilized by H-bond sub-networks organized around HUB residues and, iii) the charge content of exon 6 modulates the intrinsic structural preference of its flexible backbone, which can be described as an ensemble of conformations. Moreover, complexes between NRP-1 and VEGFA isoforms were modeled by molecular docking to study what isoforms are able to bind NRP-1. The analysis of complexes evidenced that VEGFA_121, VEGFA_145, VEGFA_183, VEGFA_189 and VEGFA_206, containing exons 7 and 8a, are able to interact with NRP-1 because they have the key regions of exons 7b and/or 8a. An overview of the isoforms shows how the fluctuations are the main guidance of their biological function. MD simulations also provide insights into factors that stabilize the binding regions of isoforms.