title: Molecular basis for the dynamic strength of the integrin alpha4beta1/VCAM-1 interaction.
abstract: Intercellular adhesion mediated by integrin alpha4beta1 and vascular cell adhesion molecule-1 (VCAM-1) plays a crucial role in both the rolling and firm attachment of leukocytes onto the vascular endothelium. Essential to the alpha4beta1/VCAM-1 interaction is its mechanical strength that allows the complex to resist the large shear forces imposed by the bloodstream. Herein we employed single-molecule dynamic force spectroscopy to investigate the dynamic strength of the alpha4beta1/VCAM-1 complex. Our force measurements revealed that the dissociation of the alpha4beta1/VCAM-1 complex involves overcoming at least two activation potential barriers: a steep inner barrier and a more elevated outer barrier. The inner barrier grants the complex the tensile strength to withstand large pulling forces (>50 pN) and was attributed to the ionic interaction between the chelated Mg2+ ion at the N-terminal A-domain of the beta1 subunit of alpha4beta1 and the carboxyl group of Asp-40 of VCAM-1 through the use of site-directed mutations. In general, additional mutations within the C-D loop of domain 1 of VCAM-1 suppressed both inner and outer barriers of the alpha4beta1/VCAM-1 complex, while a mutation at Asp-143 of domain 2 of VCAM-1 resulted in the suppression of the outer barrier, but not the inner barrier. In contrast, the outer barrier of alpha4beta1/VCAM-1 complex was stabilized by integrin activation. Together, these findings provide a molecular explanation for the functionally relevant kinetic properties of the alpha4beta1/VCAM-1 interaction.
authors.affiliation: Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida 33136, USA.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Zhang
authors.forename: Susan E
authors.initials: SE
authors.lastname: Craig
authors.forename: Hishani
authors.initials: H
authors.lastname: Kirby
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Humphries
authors.forename: Vincent T
authors.initials: VT
authors.lastname: Moy
mesh_terms: D001665:Binding Sites; D002448:Cell Adhesion / Q000502:physiology*; D002460:Cell Line; D003198:Computer Simulation; D006801:Humans; D039041:Integrin alpha4beta1 / Q000737:chemistry / Q000378:metabolism*; D008846:Micromanipulation / Q000379:methods; D018625:Microscopy, Atomic Force / Q000379:methods; D008954:Models, Biological; D008956:Models, Chemical; D009000:Monocytes / Q000737:chemistry / Q000502:physiology*; D011485:Protein Binding; D013314:Stress, Mechanical; D013329:Structure-Activity Relationship; D019010:Vascular Cell Adhesion Molecule-1 / Q000737:chemistry / Q000378:metabolism*
chemical_list: D039041:Integrin alpha4beta1; D019010:Vascular Cell Adhesion Molecule-1