RT Journal Article
SR Electronic
T1 Regulation of Cell Adhesion by Affinity and Conformational Unbending of α<sub>4</sub>β<sub>1</sub> Integrin
JF The Journal of Immunology
JO J. Immunol.
FD American Association of Immunologists
SP 6828
OP 6839
DO 10.4049/jimmunol.178.11.6828
VO 178
IS 11
A1 Chigaev, Alexandre
A1 Waller, Anna
A1 Zwartz, Gordon J.
A1 Buranda, Tione
A1 Sklar, Larry A.
YR 2007
UL http://www.jimmunol.org/content/178/11/6828.abstract
AB Rapid activation of integrins in response to chemokine-induced signaling serves as a basis for leukocyte arrest on inflamed endothelium. Current models of integrin activation include increased affinity for ligand, molecular extension, and others. In this study, using real-time fluorescence resonance energy transfer to assess α4β1 integrin conformational unbending and fluorescent ligand binding to assess affinity, we report at least four receptor states with independent regulation of affinity and unbending. Moreover, kinetic analysis of chemokine-induced integrin conformational unbending and ligand-binding affinity revealed conditions under which the affinity change was transient whereas the unbending was sustained. In a VLA-4/VCAM-1-specific myeloid cell adhesion model system, changes in the affinity of the VLA-4-binding pocket were reflected in rapid cell aggregation and disaggregation. However, the initial rate of cell aggregation increased 9-fold upon activation, of which only 2.5-fold was attributable to the increased affinity of the binding pocket. These data show that independent regulation of affinity and conformational unbending represents a novel and fundamental mechanism for regulation of integrin-dependent adhesion in which the increased affinity appears to account primarily for the increasing lifetime of the α4β1 integrin/VCAM-1 bond, whereas the unbending accounts for the increased capture efficiency.