Rolling Adhesion through an Extended Conformation of Integrin αLβ2 and Relation to α I and β I-like Domain Interaction

Abstract

In vivo, beta(2) integrins and particularly alpha(L)beta(2) (LFA-1) robustly support firm adhesion of leukocytes, but can also cooperate with other molecules in supporting rolling adhesion. Strikingly, a small molecule alpha/beta I-like allosteric antagonist, XVA143, inhibits LFA-1-dependent firm adhesion, while at the same time it enhances adhesion in shear flow and rolling both in vitro and in vivo. XVA143 appears to induce the extended conformation of integrins as shown by increased activation epitope exposure. Fab to the beta(2) I-like domain converts firm adhesion to rolling adhesion, but does not enhance adhesion. Residue alpha(L)-Glu-310 in the linker following the I domain is critical for communication to the beta(2) I-like domain, rolling, integrin extension, and activation by Mn(2+) of firm adhesion. The results demonstrate the importance of integrin extension in rolling, and suggest that rolling and firm adhesion are mediated by extended conformations of alpha(L)beta(2) that differ in the affinity of the alpha(L) I domain for ICAM-1.

The integrin α-subunit leg extends at a Ca2+-dependent epitope in the thigh/genu interface upon activation

“…As previously reported, the m24 epitope is induced by Mn 2ϩ but not PMA (9,34). These results are consistent with PMA and Mn 2ϩ each inducing extended integrin conformations but with Mn 2ϩ favoring more the extended conformation with the open headpiece (28). The exposure of activation epitopes on both the ␣ L leg and the ␤ 2 leg under the same conditions demonstrates coordinated straightening of the legs, in agreement with EM observations on ␣ V ␤ 3 (6).…”

“…We further examined the Ca 2ϩ dependence of NKI-L16 and AO3 mAb binding in the presence of the ␣͞␤ I-like allosteric antagonist XVA143, which is known to bind to the ␤ 2 I-like MIDAS and to induce extension of ␣ L ␤ 2 as reported by mAbs to ␤ 2 -subunit activation epitopes (26)(27)(28). XVA143 increased binding of NKI-L16 to LFA-1 at all Ca 2ϩ concentrations ( Fig.…”

A Small Molecule Agonist of an Integrin, αLβ2

“…2F). As demonstrated previously, the addition of compound 5 in Ca 2ϩ /Mg 2 significantly increased rolling adhesion, and Mn 2ϩ increased firm adhesion (42). At a shear stress of 2 dyn/cm 2 , compound 4 in Ca 2ϩ /Mg 2ϩ induced firm adhesion to a similar extent as observed with Mn 2ϩ alone.…”

“…Flow Chamber Assay-Binding and detachment in shear flow of ␣ L ␤ 2 transfectants on immobilized ICAM-1 substrates was done in a parallel plate flow chamber as described (42).…”

AL-57, a ligand-mimetic antibody to integrin LFA-1, reveals chemokine-induced affinity up-regulation in lymphocytes

“…For example, the epitope of mAb KIM127 used in this study maps to a ␤ 2 leg epitope that is shielded in the bent, resting integrin conformation and becomes exposed in the extended, activated state (27,28,41,51). The extended LFA-1 can contain a low-affinity, IA, or HA I domain, depending on the strength of activation and the density of ligand (9,52). Therefore, the ability of AL-57 to directly report I domain conformation allows us to define LFA-1 conformations more precisely.…”