title: Molecular basis for complement recognition by integrin αXβ2.
abstract: Integrin α(X)β(2) functions as complement receptor for iC3b and mediates recognition and phagocytosis of pathogens. We used negative-stain EM to examine the α(X)β(2) interaction with iC3b. EM class averages of α(X)β(2) in complex with iC3b define the binding sites on both the integrin and iC3b. iC3b contains C3c and thioester domain moieties linked by a long flexible linker. The binding site is on the key ring of the C3c moiety, at the interface between the MG3 and MG4 domains. Similar complexes are seen between α(X)β(2) and the C3c fragment. α(X)β(2) binds through the α(X) αI domain, on the face known to bear the metal ion-dependent adhesion site, at the opposite end of the αI domain from its site of insertion in the β-propeller domain.
authors.affiliation: Immune Disease Institute, Children's Hospital Boston, and Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Xing
authors.initials: X
authors.lastname: Chen
authors.forename: Yamei
authors.initials: Y
authors.lastname: Yu
authors.forename: Li-Zhi
authors.initials: LZ
authors.lastname: Mi
authors.forename: Thomas
authors.initials: T
authors.lastname: Walz
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
mesh_terms: D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002448:Cell Adhesion; D002845:Chromatography / Q000379:methods; D003176:Complement C3 / Q000737:chemistry; D003179:Complement C3b / Q000737:chemistry*; D003165:Complement System Proteins; D006224:Cricetinae; D006801:Humans; D016167:Integrin alphaXbeta2 / Q000378:metabolism*; D007477:Ions; D008024:Ligands; D008854:Microscopy, Electron / Q000379:methods; D008954:Models, Biological; D010587:Phagocytosis; D017434:Protein Structure, Tertiary
chemical_list: D003176:Complement C3; D016167:Integrin alphaXbeta2; D007477:Ions; D008024:Ligands; D003179:Complement C3b; D003165:Complement System Proteins