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Paper Chase

Energy landscape differences among integrins establish the framework for understanding activation.

J. Cell Biol.. Jan 02, 2018;217(1):397-412.
Li J, Springer TA.

Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA.


Why do integrins differ in basal activity, and how does affinity for soluble ligand correlate with cellular adhesiveness? We show that basal conformational equilibrium set points for integrin α4β1are cell type specific and differ from integrin α5β1when the two integrins are coexpressed on the same cell. Although α4β1is easier to activate, its high-affinity state binds vascular cell adhesion molecule and fibronectin 100- to 1,000-fold more weakly than α5β1binds fibronectin. Furthermore, the difference in affinity between the high- and low-affinity states is more compressed in α4β1(600- to 800-fold) than in α5β1(4,000- to 6,000-fold). α4β1basal conformational equilibria differ among three cell types, define affinity for soluble ligand and readiness for priming, and may reflect differences in interactions with intracellular adaptors but do not predict cellular adhesiveness for immobilized ligand. The measurements here provide a necessary framework for understanding integrin activation in intact cells, including activation of integrin adhesiveness by application of tensile force by the cytoskeleton, across ligand-integrin-adaptor complexes.