title: Anchorage-dependent binding of integrin I-domain to adhesion ligands.
abstract: The dynamic interactions between leukocyte integrin receptors and ligands in the vascular endothelium, extracellular matrix, or invading pathogens result in leukocyte adhesion, extravasation, and phagocytosis. This work examined the mechanical strength of the connection between iC3b, a complement component that stimulates phagocytosis, and the ligand-binding domain, the I-domain, of integrin αMβ2. Single-molecule force measurements of αM I-domain-iC3b complexes were conducted by atomic force microscope. Strikingly, depending on loading rates, immobilization of the I-domain via its C-terminus resulted in a 1.3-fold to 1.5-fold increase in unbinding force compared with I-domains immobilized via the N-terminus. The force spectra (unbinding force versus loading rate) of the I-domain-iC3b complexes revealed that the enhanced mechanical strength is due to a 2.4-fold increase in the lifetime of the I-domain-iC3b bond. Given the structural and functional similarity of all integrin I-domains, our result supports the existing allosteric regulatory model by which the ligand binding strength of integrin can be increased rapidly when a force is allowed to stretch the C-terminus of the I-domain. This type of mechanism may account for the rapid ligand affinity adjustment during leukocyte migration.
authors.affiliation: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Fu
authors.forename: Yan
authors.initials: Y
authors.lastname: Xu
authors.forename: Chenyu
authors.initials: C
authors.lastname: Wu
authors.forename: Vincent T
authors.initials: VT
authors.lastname: Moy
authors.forename: X Frank
authors.initials: XF
authors.lastname: Zhang
mesh_terms: D003179:Complement C3b / Q000737:chemistry*; D006801:Humans; D055767:Immobilized Proteins / Q000737:chemistry*; D008024:Ligands; D016177:Macrophage-1 Antigen / Q000737:chemistry*; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: D055767:Immobilized Proteins; D008024:Ligands; D016177:Macrophage-1 Antigen; D003179:Complement C3b
keywords: atomic force microscopy; cell adhesion; integrin; single-molecule force spectroscopy