Two-dimensional kinetics regulation of alphaLbeta2-ICAM-1 interaction by conformational changes of the alphaL-inserted domain.
The leukocyte integrin alphaLbeta2 mediates cell adhesion and migration during inflammatory and immune responses. Ligand binding of alphaLbeta2 is regulated by or induces conformational changes in the inserted (I) domain. By using a micropipette, we measured the conformational regulation of two-dimensional (2D) binding affinity and the kinetics of cell-bound intercellular adhesion molecule-1 interacting with alphaLbeta2 or isolated I domain expressed on K562 cells. Locking the I domain into open and intermediate conformations with a disulfide bond increased the affinities by approximately 8000- and approximately 30-fold, respectively, from the locked closed conformation, which has similar affinity as the wild-type I domain. Most surprisingly, the 2D affinity increases were due mostly to the 2D on-rate increases, as the 2D off-rates only decreased by severalfold. The wild-type alphaLbeta2, but not its I domain in isolation, could be up-regulated by Mn2+ or Mg2+ to have high affinities and on-rates. Locking the I domain in any of the three conformations abolished the ability of divalent cations to regulate 2D affinity. These results indicate that a downward displacement of the I domain C-terminal helix, induced by conformational changes of other domains of the alphaLbeta2, is required for affinity and on-rate up-regulation.
Zhang
Fang
F
Coulter Department of Biomedical Engineering and Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
Marcus
Warren D
WD
Goyal
Nimita H
NH
Selvaraj
Periasamy
P
Springer
Timothy A
TA
Zhu
Cheng
C
D000818:Animals; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000737:chemistry* / Q000378:metabolism; D020014:K562 Cells; D007700:Kinetics; D051379:Mice; D011485:Protein Binding; D011487:Protein Conformation; D020349:Surface Plasmon Resonance
D017261:Glycosylphosphatidylinositols; D018799:Intercellular Adhesion Molecule-1