Heterotropic roles of divalent cations in the establishment of allostery and affinity maturation of integrin αXβ2

Allosteric activation and silencing of leukocyte beta 2-integrins transpire through cation-dependent structural changes, which mediate integrin biosynthesis and recycling, and are essential to designing leukocyte -specific drugs. Stepwise addition of Mg2+ reveals two mutually coupled events for the alpha X beta 2 ligand-binding domain-the alpha X I-domain-corresponding to allostery establishment and affinity maturation. Electrostatic alterations in the Mg2+-binding site establish long-range couplings, leading to both pH-and Mg2+-occu-pancy-dependent biphasic stability change in the alpha X I-domain fold. The ligand-binding sensorgrams show composite affinity events for the alpha X I-domain accounting for the multiplicity of the aX I-domain conformational states existing in the solution. On cell surfaces, increasing Mg2+ concentration enhanced adhesiveness of alpha X beta 2. This work highlights how intrinsically flexible pH-and cation-sensitive architecture endows a unique dynamic continuum to the aIdomain structure on the intact integrin, thereby revealing the importance of allostery establishment and affinity maturation in both extracellular and intracellular integrin events.

Automated summary

Allosteric activation and silencing of leukocyte beta 2-integrins occur through cation-dependent structural changes, which are essential for designing leukocyte-specific drugs. The study reveals that the alpha X I-domain exhibits composite affinity events in response to pH and Mg2+ conditions, and increasing Mg2+ concentration enhances the adhesiveness of alpha X beta 2 on cell surfaces.