7la4

Integrin AlphaIIbBeta3-PT25-2 Complex

spinqualitylabelsall models 7la4, resolution 3.30Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 7la4 is a 4 chain structure with sequence from Homo sapiens and Mus musculus. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: Electron Microscopy, Resolution 3.3Å Ligands: CA, MAN, MG, NAG Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Disease ITA2B_HUMAN Defects in ITGA2B are a cause of Glanzmann thrombasthenia (GT) [MIM:273800; also known as thrombasthenia of Glanzmann and Naegeli. GT is the most common inherited disease of platelets. It is an autosomal recessive disorder characterized by mucocutaneous bleeding of mild-to-moderate severity and the inability of this integrin to recognize macromolecular or synthetic peptide ligands. GT has been classified clinically into types I and II. In type I, platelets show absence of the glycoprotein IIb/beta-3 complexes at their surface and lack fibrinogen and clot retraction capability. In type II, the platelets express the glycoprotein IIb/beta-3 complex at reduced levels (5-20% controls), have detectable amounts of fibrinogen, and have low or moderate clot retraction capability. The platelets of GT 'variants' have normal or near normal (60-100%) expression of dysfunctional receptors. Function ITA2B_HUMAN Integrin alpha-IIb/beta-3 is a receptor for fibronectin, fibrinogen, plasminogen, prothrombin, thrombospondin and vitronectin. It recognizes the sequence R-G-D in a wide array of ligands. It recognizes the sequence H-H-L-G-G-G-A-K-Q-A-G-D-V in fibrinogen gamma chain. Following activation integrin alpha-IIb/beta-3 brings about platelet/platelet interaction through binding of soluble fibrinogen. This step leads to rapid platelet aggregation which physically plugs ruptured endothelial cell surface. Publication Abstract from PubMed The murine monoclonal antibody (mAb) PT25-2 induces alphaIIbbeta3 to bind ligand and initiate platelet aggregation. The underlying mechanism is unclear, because previous mutagenesis studies suggested that PT25-2 binds to the alphaIIb beta propeller, a site distant from the Arg-Gly-Asp-binding pocket. To elucidate the mechanism, we studied the alphaIIbbeta3-PT25-2 Fab complex by negative-stain and cryo-electron microscopy (EM). We found that PT25-2 binding results in alphaIIbbeta3 partially exposing multiple ligand-induced binding site epitopes and adopting extended conformations without swing-out of the beta3 hybrid domain. The cryo-EM structure showed PT25-2 binding to the alphaIIb residues identified by mutagenesis but also to 2 additional regions. Overlay of the cryo-EM structure with the bent alphaIIbbeta3 crystal structure showed that binding of PT25-2 creates clashes with the alphaIIb calf-1/calf-2 domains, suggesting that PT25-2 selectively binds to partially or fully extended receptor conformations and prevents a return to its bent conformation. Kinetic studies of the binding of PT25-2 compared with mAbs 10E5 and 7E3 support this hypothesis. We conclude that PT25-2 induces alphaIIbbeta3 ligand binding by binding to extended conformations and by preventing the interactions between the alphaIIb and beta3 leg domains and subsequently the betaI and beta3 leg domains required for the bent-closed conformation. , PMID:33760023 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See Also Integrin 3D structures Monoclonal Antibodies 3D structures

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