Conformational equilibria and intrinsic affinities define integrin activation. (25th January 2017)

• Record Type: Journal Article
• Authors: Li, Jing; Su, Yang; Xia, Wei; Qin, Yan; Humphries, Martin J; Vestweber, Dietmar; Cabañas, Carlos; Lu, Chafen; Springer, Timothy A
• Is Part Of: EMBO journal. Volume 36:Number 5(2017)
• Page Start: 629
• Page End: 645
• Publication Date: 2017-01-25
• Subjects: affinity -- conformation -- integrin -- N‐glycan -- thermodynamics; Molecular biology -- Periodicals; 572.805
• DOI: 10.15252/embj.201695803
• Languages: English
• ISSNs: 0261-4189

Abstract

Abstract: We show that the three conformational states of integrin α5 β1 have discrete free energies and define activation by measuring intrinsic affinities for ligand of each state and the equilibria linking them. The 5, 000‐fold higher affinity of the extended‐open state than the bent‐closed and extended‐closed states demonstrates profound regulation of affinity. Free energy requirements for activation are defined with protein fragments and intact α5 β1 . On the surface of K562 cells, α5 β1 is 99.8% bent‐closed. Stabilization of the bent conformation by integrin transmembrane and cytoplasmic domains must be overcome by cellular energy input to stabilize extension. Following extension, headpiece opening is energetically favored. N‐glycans and leg domains in each subunit that connect the ligand‐binding head to the membrane repel or crowd one another and regulate conformational equilibria in favor of headpiece opening. The results suggest new principles for regulating signaling in the large class of receptors built from extracellular domains in tandem with single‐span transmembrane domains. Synopsis: Thermodynamic analysis of the three integrin α5 β1 conformation states offers a model for signaling regulation via an interplay between extracellular and transmembrane/intracellular domains in a large class of receptors built from multiple domains. The integrin extended‐open state has 5, 000‐fold higher ligand affinity than the bent‐closed and extended‐closed states. Interactions between N‐glycosylated leg domains of integrin alpha and beta subunits regulate conformational equilibria in favor of headpiece opening. Almost all α5 β1 integrins on the cell surface are in a bent‐closed conformation. Stabilization of the bent conformation by integrin transmembrane and cytoplasmic domains must be overcome by cellular energy input to establish the high affinity, extended‐open state. Abstract : Thermodynamic and intrinsic affinity measurements show how intramolecular interactions of integrin receptor domains and post‐translational modifications regulate activation of ligand binding.