Structure-guided design of a high-affinity platelet integrin αIIbβ3 receptor antagonist that disrupts Mg²⁺ binding to the MIDAS. Sci Transl Med 2012 Mar 14;4(125):125ra32
Date
03/17/2012Pubmed ID
22422993Pubmed Central ID
PMC3390238DOI
10.1126/scitranslmed.3003576Scopus ID
2-s2.0-84863375270 (requires institutional sign-in at Scopus site) 68 CitationsAbstract
An integrin found on platelets, α(IIb)β(3) mediates platelet aggregation, and α(IIb)β(3) antagonists are effective antithrombotic agents in the clinic. Ligands bind to integrins in part by coordinating a magnesium ion (Mg(2+)) located in the β subunit metal ion-dependent adhesion site (MIDAS). Drugs patterned on the integrin ligand sequence Arg-Gly-Asp have a basic moiety that binds the α(IIb) subunit and a carboxyl group that coordinates the MIDAS Mg(2+) in the β(3) subunits. They induce conformational changes in the β(3) subunit that may have negative consequences such as exposing previously hidden epitopes and inducing the active conformation of the receptor. We recently reported an inhibitor of α(IIb)β(3) (RUC-1) that binds exclusively to the α(IIb) subunit; here, we report the structure-based design and synthesis of RUC-2, a RUC-1 derivative with a ~100-fold higher affinity. RUC-2 does not induce major conformational changes in β(3) as judged by monoclonal antibody binding, light scattering, gel chromatography, electron microscopy, and a receptor priming assay. X-ray crystallography of the RUC-2-α(IIb)β(3) headpiece complex in 1 mM calcium ion (Ca(2+))/5 mM Mg(2+) at 2.6 Å revealed that RUC-2 binds to α(IIb) the way RUC-1 does, but in addition, it binds to the β(3) MIDAS residue glutamic acid 220, thus displacing Mg(2+) from the MIDAS. When the Mg(2+) concentration was increased to 20 mM, however, Mg(2+) was identified in the MIDAS and RUC-2 was absent. RUC-2's ability to inhibit ligand binding and platelet aggregation was diminished by increasing the Mg(2+) concentration. Thus, RUC-2 inhibits ligand binding by a mechanism different from that of all other α(IIb)β(3) antagonists and may offer advantages as a therapeutic agent.
Author List
Zhu J, Choi WS, McCoy JG, Negri A, Zhu J, Naini S, Li J, Shen M, Huang W, Bougie D, Rasmussen M, Aster R, Thomas CJ, Filizola M, Springer TA, Coller BSAuthor
Jieqing Zhu PhD Assistant Professor, Associate Investigator in the Biochemistry department at BloodCenter of WisconsinMESH terms used to index this publication - Major topics in bold
AnimalsBinding Sites
Blood Platelets
Cell Adhesion
Collagen
Crystallography, X-Ray
Fibrinogen
Humans
Magnesium
Mice
Microscopy, Electron
Oligopeptides
Platelet Aggregation
Platelet Aggregation Inhibitors
Platelet Glycoprotein GPIIb-IIIa Complex
Protein Binding
Rats
Vitronectin
