An atomic resolution view of ICAM recognition in a complex between the binding domains of ICAM-3 and integrin α_Lβ₂

Abstract

Within the Ig superfamily (IgSF), intercellular adhesion molecules (ICAMs) form a subfamily that binds the leukocyte integrin ␣L␤2. We report a 1.65-Å-resolution crystal structure of the ICAM-3 N-terminal domain (D1) in complex with the inserted domain, the ligand-binding domain of ␣L␤2. This high-resolution structure and comparisons among ICAM subfamily members establish that the binding of ICAM-3 D1 onto the inserted domain represents a common docking mode for ICAM subfamily members. The markedly different off-rates of ICAM-1, -2, and -3 appear to be determined by the hydrophobicity of residues that surround a metal coordination bond in the ␣L␤2-binding interfaces. Variation in composition of glycans on the periphery of the interfaces influences on-rate. structure ͉ protein recognition ͉ cell adhesion ͉ LFA-1

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

“…MHM24 showed comparable binding and dissociation constants (K D ) to WT disulfidelocked, IA L161C͞F299C and HA K287C͞K297C mutant I domains (31) (Fig. 1A and Most ligands to integrins, including ICAM-1, use an acidic residue to directly coordinate a magnesium ion at the metal ion-dependent adhesion site of the integrin I domain (31,37,38). The ligand-mimetic properties of the AL-57͞LFA-1 interaction, especially the Mg 2ϩ dependence of binding, led us to hypothesize that an interaction with an acidic residue in AL-57 is also required for I domain binding.…”

Structural basis of activation-dependent binding of ligand-mimetic antibody AL-57 to integrin LFA-1

“…These include Trp-52 of CDR2H, Tyr-100, Phe-102, and Trp-103 of CDR3H, as well as Tyr-32 of CDR1L and Tyr-92 of CDR3L. This kind of hydrophobic cluster is not seen in the interface between ICAMs and the I domain (14,15). The highly hydrophobic nature of the AL-57 interface clearly explains the 250-fold slower off-rate of AL-57 binding to the high-affinity ␣ L I domain compared to that observed in ICAM-1 binding, as demonstrated in our comparative binding studies on ICAM-1 and ICAM-3 (14).…”

“…This kind of hydrophobic cluster is not seen in the interface between ICAMs and the I domain (14,15). The highly hydrophobic nature of the AL-57 interface clearly explains the 250-fold slower off-rate of AL-57 binding to the high-affinity ␣ L I domain compared to that observed in ICAM-1 binding, as demonstrated in our comparative binding studies on ICAM-1 and ICAM-3 (14). Overall, such highly favored interface and binding kinetics strongly suggest that AL-57 acts as a ligand-mimetic that is strongly competitive with the native ligand.…”

“…The binding preference of AL-57 has now been demonstrated by comparative structural studies. Early structural data have shown that ICAM family members share the same binding mode to the LFA-1 I domain (7,14,15). Central in the binding site is an invariant acidic residue designated Glu-37 (the residue numbering follows ICAM-3's nomenclature throughout) coordinating to the MIDAS metal ion.…”

“…This flipping of Gly-240 is coupled to the movement of the immediately neighboring Asp-239, which pulls this MIDAS coordinating residue away from any direct coordination to the metal, as discussed above. Consequently, the flipping movement also leads to the reorientation of the downstream neighboring Glu-241 into a favorable position, enabling a crucial electrostatic interaction to the basic residue Lys-42 from ligand ICAM-3 (or Lys-39 in ICAM-1 and Arg-42 in ICAM-5) (7,14,15). In the current AL-57/IA structure, there occurred a similar interaction between Glu-241 and AL-57's Arg-31(H) (Fig.…”