An study reveals that a C-terminal fragment of the adhesion protein Fibulin7 (Fbln7-C) regulates the activation of integrin α5β1 through dynamics of VWA and the hybrid domain in the β1 subunit.

A C-terminal fragment of the adhesion protein Fibulin7 (Fbln7-C) binds to monocytes and neutrophils integrin α5β1, regulating their adhesion and immunological functions through Erk and STAT signaling pathways. It also inhibits cell binding, spreading, and migration on fibronectin. However, the precise structural components of Fbln7-C that interact with various domains of integrin α5β1 and contribute to its regulatory effects are not entirely understood. This study investigated the structural dynamics of Fibulin7 fragments and the mechanisms by which Fbln7-C regulates α5β1 integrin activation using protein modeling, protein-protein docking, molecular dynamics simulation (MDS), and binding free energy calculations. An energy-minimized model of α5β1 integrin, Fibulin7 full length (Fbln7-FL), and Fbln7-C was developed and validated using 100 ns MDS. Additionally, protein-protein docking was used to confirm Fbln7-C's better integrin binding ability over Fbln7-FL. A 500 ns MDS on the docked Fbln7-C integrin complex revealed the regulatory effects of Fbln7-C on arginine-glycine-aspartic acid (RGD) bound integrin α5β1. The simulation studies showed that Fbln7-C's attachment to activated α5β1 integrin increased the distance between the RGD and its interacting residues on both integrin subunits, shifting the RGD ligand from its original binding position and inactivating the integrin. Further analysis using free energy landscape (FEL), principal component analysis (PCA), and binding energy calculation validated the alteration in α5β1 integrin's structural dynamics following Fbln7-C binding. This could relate to obstruction in the outward swing of the integrin's hybrid domain and result in the low-affinity, inactive headpiece conformation of the α5β1 integrin.