title: Closed headpiece of integrin αIIbβ3 and its complex with an αIIbβ3-specific antagonist that does not induce opening.
abstract: The platelet integrin α(IIb)β(3) is essential for hemostasis and thrombosis through its binding of adhesive plasma proteins. We have determined crystal structures of the α(IIb)β(3) headpiece in the absence of ligand and after soaking in RUC-1, a novel small molecule antagonist. In the absence of ligand, the α(IIb)β(3) headpiece is in a closed conformation, distinct from the open conformation visualized in presence of Arg-Gly-Asp (RGD) antagonists. In contrast to RGD antagonists, RUC-1 binds only to the α(IIb) subunit. Molecular dynamics revealed nearly identical binding. Two species-specific residues, α(IIb) Y190 and α(IIb) D232, in the RUC-1 binding site were confirmed as important by mutagenesis. In sharp contrast to RGD-based antagonists, RUC-1 did not induce α(IIb)β(3) to adopt an open conformation, as determined by gel filtration and dynamic light scattering. These studies provide insights into the factors that regulate integrin headpiece opening, and demonstrate the molecular basis for a novel mechanism of integrin antagonism.
authors.affiliation: Immune Disease Institute, Children's Hospital Boston, and Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Jieqing
authors.initials: J
authors.lastname: Zhu
authors.forename: Jianghai
authors.initials: J
authors.lastname: Zhu
authors.forename: Ana
authors.initials: A
authors.lastname: Negri
authors.forename: Davide
authors.initials: D
authors.lastname: Provasi
authors.forename: Marta
authors.initials: M
authors.lastname: Filizola
authors.forename: Barry S
authors.initials: BS
authors.lastname: Coller
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
mesh_terms: D000818:Animals; D001665:Binding Sites; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D016297:Mutagenesis, Site-Directed; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005340:Fibrinogen