Synthetic Biology

Biography

Biography: Mehmet Sen

Abstract

The mechanism through which adhesiveness of lymphocyte function-associated antigen-1 (LFA-1) is the consequence of highly coordinated structural rearrangements within both α and β subunits yet, atomic details of LFA-1 conformations remain to be investigated. Here we determined the crystal structures of the LFA-1 headpiece that shows coordinations of cations in the closed conformation. The external ligand binding (αI) domain provides striking interdomain flexibility, which potentially plays a pivotal role for greater accessibility in ligand recognition. Loops at the αI and β-propeller interface for the αL and αX differ in length, orientation and post-translational modifications. Moreover we also characterize in atomic details of how a shape-shifting pathway of the β2 I-domain regulates its affinity for the internal ligand, which occurs in a different order than in β1, β3 and β6 integrins. Small angle x-ray scattering (SAXS), negative stain electron microscopy (EM) and adhesion assays here show that LFA-1 activation requires headpiece opening event. Mn2+, universal integrin activator together with the high-affinity ICAM-1 ectodomain was examined for the effect on the equilibrium between the open and closed LFA-1 headpiece conformations. Mn2+, relative to the Mg2+ shifted the equilibrium toward the open conformation. Addition of ICAM-1 substantially stabilized the open headpiece. The observed headpiece opening upon addition of Mn2+ and ICAM-1 is consistent with our previous structural studies and headpiece-opening model.. Furthermore, our adhesion assays revealed that an activating and inhibiting βI mutations stabilized the open/extended and bent/closed integrin states, respectively, which provides a structural mechanism into a leukocyte adhesion deficiency (LAD-I) mutation.