Title: Activation Mechanisms of αVβ3 Integrin by Binding to Fibronectin: A Computational Study
Abstract: Integrins are αβ heterodimeric transmembrane receptors that mediate cell-cell and cell-matrix adhesion through interactions with ligands (Cell 69, 11, 1992). αVβ3 integrin is a receptor important in tumor angiogenesis and metastasis, inflammation, and bone resorption (J. Clin. Invest. 103, 1227, 1999). αVβ3 integrin binds to multiple ligands including extracellular matrix protein fibronectin to regulate cellular activities (J. Biol. Chem. 275, 21785, 2000). The structural bases of activation and regulation of αVβ3 integrin by binding to fibronectin remain unclear. This study investigated the conformational and dynamical motion changes of the extracellular domain of αVβ3 integrin by binding to fibronectin. We constructed αVβ3-fibronectin complex based on the crystal structure of the extracellular domain of αVβ3 integrin in complex with RGD ligand (Science 296, 151) and the crystal structure of module 9 and 10 of fibronectin (Cell 84:155) through geometrically fitting, and the missing residues in αV and β3 subunit were constructed using homology modeling. We performed 180 ns molecular dynamics simulations to determine the changes of the conformation, dynamical motion and cation Mn2+ binding in αVβ3 induced by ligation with fibronectin. Results showed that fibronectin binding to αVβ3 resulted in the changes of dynamical motion between different domains of αV and β3 subunit. These dynamical motions caused the tendency of the opening conformation between the head and tail regions of αVβ3 and the orientation change between hybrid domain and βA domain in β3 subunit with swing-out tendency, which contributed to αVβ3 activation. We observed the relative movement between α1 and α7 helix in βA domain and stabilized cation Mn2+ binding in αVβ3 by ligation with fibronectin, which were directly correlated with αVβ3 activation. Results provide molecular and structural insight for the activation mechanisms of αVβ3 integrin by binding to fibronectin.