Springer, Timothy A. Project 1 Recognition by the platelet integrin alphaiibB3 of macromolecular ligands, particulariy fibrinogen, is a key step in hemostasis. Activation of alphaiibB3 involves some of the largest conformational changes known in proteins, including leg extension and head opening. Several therapeutics that target alphaiibB3 are used during percutaneous interventions;however, they also induce the active conformation and can lead to thrombocytopenia. Understanding the structure of integrin alphaiibB3, how its conformation is regulated during platelet activation, and how it binds to macromolecular ligands and small molecule therapeutics, is key to a better understanding of vascular processes and developing improved therapeutics. Furthermore, alphaiibB3 is a common target of antibodies that are responsible for immune thrombocytopenia purpura (ITP), and understanding the molecular basis of ITP is important for improvements in therapy.
Four aims address these needs. 1. Crystal structures and molecular dynamics examine the atomic pathway between the closed and open headpieces, including four intermediate states, and demonstrate opening by RGD and therapeutic RGD-mimetics of the headpiece. Structures of alphaiibB3 bound to RUC-2 advance second-generation integrin antagonists that do not induce opening. 2. How alphaiibB3 recognizes macromolecular ligands will be examined with complexes with one or more ligands including the fibrinogen yC module, fibronectin Fn3 modules 9 and 10, Del-1 EGF domains, and a disintegrin. The structures will show how the non-RGD portions of ligands contribute specificity and affinity. 3. We examine the biology of integrin activafion by measuring monomeric affinity for the fibrinogen yC module on resting and activated platelets. The effects of function-perturbing or function-dependent Fab including LIBS Fab and ligand-mimetic Fab are correlated with the conformation of intact alphaiibB3 in complex with the Fab in EM. 4. We will examine the structural basis of ITP. Crystal structures of drug-dependent complexes between Fab and alphaiibB3 are examined in model systems using a drug with no known propensity for alphaiibB3 (quinine) or a specific antagonist (eptifibatide). A new concept is advanced that drugs can perturb the backbone conformation of antibody variable region loops. Complexes with intact alphaiibB3 in EM examine specificity of drug-dependent Fab from patients with ITP.
R E L E V A N C E (See instructions) structures of molecules on platelets are important to understand disorders of bleeding and thrombosis, and immune destruction of platelets. The structures determined in this work will be important for development of drugs to prevent thrombosis, and improved treatments of patients that have bleeding disorders due to abnormally low numbers of platelets.
|Lin, Fu-Yang; Zhu, Jianghai; Eng, Edward T et al. (2016) Î²-Subunit Binding Is Sufficient for Ligands to Open the Integrin Î±IIbÎ²3 Headpiece. J Biol Chem 291:4537-46|
|Dev, Jyoti; Park, Donghyun; Fu, Qingshan et al. (2016) Structural basis for membrane anchoring of HIV-1 envelope spike. Science 353:172-5|
|Fu, Qingshan; Fu, Tian-Min; Cruz, Anthony C et al. (2016) Structural Basis and Functional Role of Intramembrane Trimerization of the Fas/CD95 Death Receptor. Mol Cell 61:602-13|
|Chou, James J; Wang, Jia-huai (2015) Transmembrane signaling: A multiplex problem with converging solutions. Prog Biophys Mol Biol 118:87-8|
|Finci, L; Zhang, Y; Meijers, R et al. (2015) Signaling mechanism of the netrin-1 receptor DCC in axon guidance. Prog Biophys Mol Biol 118:153-60|
|Zhu, Jianghai; Zhu, Jieqing; Bougie, Daniel W et al. (2015) Structural basis for quinine-dependent antibody binding to platelet integrin Î±IIbÎ²3. Blood 126:2138-45|
|Chen, Xinping; Zhao, Chunyue; Li, Xiaolong et al. (2015) Terazosin activates Pgk1 and Hsp90 to promote stress resistance. Nat Chem Biol 11:19-25|
|Xia, Wei; Springer, Timothy A (2014) Metal ion and ligand binding of integrin Î±5Î²1. Proc Natl Acad Sci U S A 111:17863-8|
|Blenner, Mark A; Dong, Xianchi; Springer, Timothy A (2014) Structural basis of regulation of von Willebrand factor binding to glycoprotein Ib. J Biol Chem 289:5565-79|
|OuYang, Bo; Chou, James J (2014) The minimalist architectures of viroporins and their therapeutic implications. Biochim Biophys Acta 1838:1058-67|
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