Dissecting intrinsic and ligand-induced structural communication in the β3 headpiece of integrins.
Graph theory is widely used to dissect structural communication in biomolecular systems. Here, graph theory-based approaches were applied to the headpiece of integrins, adhesion cell-surface receptors that transmit signals across the plasma membranes. Protein Structure Network (PSN) analysis incorporating dynamic information either from molecular dynamics simulations or from Elastic Network Models was applied to the β3 domains from integrins αVβ3 and αIIbβ3 in their apo and ligand-bound states. Closed and open states of the β headpiece are characterized by distinct allosteric communication pathways involving highly conserved amino acids at the two different α/β interfaces in the βI domain, the closed state being prompted to the closed-to-open transition. In the closed state, pure antagonism is associated with the establishment of communication pathways that start from the ligand, pass through the β1/α3,α4 interface, and end up in the hybrid domain by involving the Y110-Q82 link, which is weakened in the agonist-bound states. Allosteric communication in integrins relies on highly conserved and functionally relevant amino acid residues. The αβα-sandwich architecture of integrin βI domain dictates the structural communication between ligand binding site and hybrid domain. Differently from agonists, pure antagonists are directly involved in allosteric communication pathways and exert long-distance strengthening of the βI/hybrid interface. Release of the structure network in the ligand binding site is associated with the close-to-open transition accompanying the activation process. The study strengthens the power of graph-based analyses to decipher allosteric communication intrinsic to protein folds and modified by functionally different ligands.