title: Locking the beta3 integrin I-like domain into high and low affinity conformations with disulfides.
abstract: Although integrin alpha subunit I domains exist in multiple conformations, it is controversial whether integrin beta subunit I-like domains undergo structurally analogous movements of the alpha7-helix that are linked to affinity for ligand. Disulfide bonds were introduced into the beta(3) integrin I-like domain to lock its beta6-alpha7 loop and alpha7-helix in two distinct conformations. Soluble ligand binding, ligand mimetic mAb binding and cell adhesion studies showed that disulfide-bonded receptor alpha(IIb)beta(3)(T329C/A347C) was locked in a low affinity state, and dithiothreitol treatment restored the capability of being activated to high affinity binding; by contrast, disulfide-bonded alpha(IIb)beta(3)(V332C/M335C) was locked in a high affinity state. The results suggest that activation of the beta subunit I-like domain is analogous to that of the alpha subunit I domain, i.e. that axial movement in the C-terminal direction of the alpha7-helix is linked to rearrangement of the I-like domain metal ion-dependent adhesion site into a high affinity conformation.
authors.affiliation: CBR Institute fo Biomedical Research and Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Bing-Hao
authors.initials: BH
authors.lastname: Luo
authors.forename: Junichi
authors.initials: J
authors.lastname: Takagi
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
mesh_terms: D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D004220:Disulfides; D004305:Dose-Response Relationship, Drug; D000939:Epitopes; D005340:Fibrinogen / Q000737:chemistry; D006801:Humans; D039661:Integrin beta3 / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014162:Transfection
chemical_list: D004220:Disulfides; D000939:Epitopes; D039661:Integrin beta3; D008024:Ligands; D005340:Fibrinogen