National Center for
5E6V: Re-refinement Of The Crystal Structure Of The Plexin-semaphorin- Integrin Domain/hybrid Domain/i-egf1 Segment From The Human Integrin B2 Subunit
Leukocyte integrin alphaLbeta2 headpiece structures: The alphaI domain, the pocket for the internal ligand, and concerted movements of its loops
Proc. Natl. Acad. Sci. U. S. A. (2016) 113 p.2940-2945
High-resolution crystal structures of the headpiece of lymphocyte function-associated antigen-1 (integrin alphaLbeta2) reveal how the alphaI domain interacts with its platform formed by the alpha-subunit beta-propeller and beta-subunit betaI domains. The alphaLbeta2 structures compared with alphaXbeta2 structures show that the alphaI domain, tethered through its N-linker and a disulfide to a stable beta-ribbon pillar near the center of the platform, can undergo remarkable pivoting and tilting motions that appear buffered by N-glycan decorations that differ between alphaL and alphaX subunits. Rerefined beta2 integrin structures reveal details including pyroglutamic acid at the beta2 N terminus and bending within the EGF1 domain. Allostery is relayed to the alphaI domain by an internal ligand that binds to a pocket at the interface between the beta-propeller and betaI domains. Marked differences between the alphaL and alphaX subunit beta-propeller domains concentrate near the binding pocket and alphaI domain interfaces. Remarkably, movement in allostery in the betaI domain of specificity determining loop 1 (SDL1) causes concerted movement of SDL2 and thereby tightens the binding pocket for the internal ligand.