The interactions between cell surface receptors and sulfated glucosamineglycans serve ubiquitous roles in cell adhesion and receptor signaling. Heparin, a highly sulfated polymer of uronic acids and glucosamine, binds strongly to the integrin receptor alphaXbeta2 (p150,95, CD11c/CD18). Here, we analyze the structural motifs within heparin that constitute high affinity binding sites for the I domain of integrin alphaXbeta2. Heparin oligomers with chain lengths of 10 saccharide residues or higher provide strong inhibition of the binding by the alphaX I domain to the complement fragment iC3b. By contrast, smaller oligomers or the synthetic heparinoid fondaparinux were not able to block the binding. Semipurified heparin oligomers with 12 saccharide residues identified the fully sulfated species as the most potent antagonist of iC3b, with a 1.3 microM affinity for the alphaX I domain. In studies of direct binding by the alphaX I domain to immobilized heparin, we found that the interaction is conformationally regulated and requires Mg2+. Furthermore, the fully sulfated heparin fragment induced conformational change in the ectodomain of the alphaXbeta2 receptor, also demonstrating allosteric linkage between heparin binding and integrin conformation.
Publications
Binding between the integrin αXβ2 (CD11c/CD18) and heparin. J Biol Chem. 282, 42, 30869-77 (2007).Abstract
Tests of the Extension and Deadbolt Models of Integrin Activation. J Biol Chem. 282, 16, 11914-20 (2007).Abstract
The connection between metal ion affinity and ligand affinity in integrin I domains. Biochim Biophys Acta. 1774, 9, 1148-55 (2007).Abstract
Requirement of α and β subunit transmembrane helix separation for integrin outside-in signaling. Blood 110, 7, 2475-83 (2007).Abstract
Specific and covalent labeling of a membrane protein with organic fluorochromes and quantume dots. Proc Natl Acad Sci USA 104, 37, 14753-8 (2007).Abstract
Structural plasticity in IgSF domain 4 of ICAM-1 mediates cell surface dimerization. Proc Natl Acad Sci USA 104, 39, 15358-63 (2007).Abstract
Structural transitions of complement component C3 and its activation products. Proc Natl Acad Sci USA 103, 52, 19737-42 (2006).Abstract
Importance of force linkage in mechanochemistry of adhesion receptors. Biochemistry 45, 50, 15020-8 (2006).Abstract
Complement and the multifaceted functions of VWA and integrin I domains. Structure 14, 11, 1611-6 (2006).Abstract
AL-57, a ligand-mimetic antibody to integrin LFA-1, reveals chemokine-induced affinity upregulation in lymphocytes. Proc Natl Acad Sci USA 103, 38, 13991-13996 (2006).Abstract
Activation of leukocyte β2 integrins by conversion from bent to extended conformations. Immunity 25, 4, 583-594 (2006).Abstract
Transition from rolling to firm adhesion can be mimicked by extension of integrin αLβ2 in an intermediate-affinity state. J Biol Chem. 281, 16, 10876-10882 (2006).Abstract
A high affinity human antibody antagonist of P-selectin mediated rolling. Biochem. Biophys. Res. Commun. 350, 3, 508-513 (2006).Abstract
Directed evolution to probe protein allostery and integrin I domains of 200,000-fold higher affinity. Proc Natl Acad Sci USA 103, 15, 5758-5763 (2006).Abstract
Integrin structures and conformational signaling. Curr Opin Cell Biol. 18, 5, 579-586 (2006).Abstract
Remodeling of the lectin/EGF-like interface in P- and L-selectin increases adhesiveness and shear resistance under hydrodynamic force. Nat. Immunol. 7, 8, 883-889 (2006).Abstract