Glycoprotein IIb/IIIa

In medicine, glycoprotein IIb/IIIa (GPIIb/IIIa, also known as integrin αIIbβ3) is an integrin complex found on platelets. It is a receptor for fibrinogen[1] and von Willebrand factor and aids platelet activation. The complex is formed via calcium-dependent association of gpIIb and gpIIIa, a required step in normal platelet aggregation and endothelial adherence.[2][3] Platelet activation by ADP (blocked by clopidogrel) leads to the aforementioned conformational change in platelet gpIIb/IIIa receptors that induces binding to fibrinogen.[1] The gpIIb/IIIa receptor is a target of several drugs including abciximab, eptifibatide, and tirofiban.

integrin, alpha 2b (platelet glycoprotein IIb of IIb/IIIa complex, antigen CD41)
Identifiers
SymbolITGA2B
Alt. symbolsGP2B
NCBI gene3674
HGNC6138
OMIM607759
RefSeqNM_000419
UniProtP08514
Other data
LocusChr. 17 q21.32
integrin, beta 3 (platelet glycoprotein IIIa, antigen CD61)
Identifiers
SymbolITGB3
Alt. symbolsGP3A
NCBI gene3690
HGNC6156
OMIM173470
RefSeqNM_000212
UniProtP05106
Other data
LocusChr. 17 q21.32

gpIIb/IIIa complex formation

Once platelets are activated, granules secrete clotting mediators, including both ADP and TXA2. These then bind their respective receptors on platelet surfaces, in both an autocrine and paracrine fashion (binds both itself and other platelets). The binding of these receptors result in a cascade of events resulting in an increase in intracellular calcium (e.g. via Gq receptor activation leading to Ca2+ release from platelet endoplasmic reticulum Ca2+ stores, which may activate PKC). Hence, this calcium increase triggers the calcium-dependent association of gpIIb and gpIIIa to form the activated membrane receptor complex gpIIb/IIIa, which is capable of binding fibrinogen (factor I), resulting in many platelets "sticking together" as they may connect to the same strands of fibrinogen, resulting in a clot. The coagulation cascade then follows to stabilize the clot, as thrombin (factor IIa) converts the soluble fibrinogen into insoluble fibrin strands. These strands are then cross-linked by factor XIII to form a stabilized blood clot.

Pathology

Defects in glycoprotein IIb/IIIa cause Glanzmann's thrombasthenia.[4]

Autoantibodies against IIb/IIIa can be produced in immune thrombocytopenic purpura.[5]

Medicine

Glycoprotein IIb/IIIa inhibitors can be used to prevent blood clots in an effort to decrease the risk of heart attack or stroke.

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See also

References
  1. Vickers JD (July 1999). "Binding of polymerizing fibrin to integrin alpha(IIb)beta(3) on chymotrypsin-treated rabbit platelets decreases phosphatidylinositol 4,5-bisphosphate and increases cytoskeletal actin". Platelets. 10 (4): 228–37. doi:10.1080/09537109976077. PMID 16801097.
  2. Calvete JJ (April 1995). "On the structure and function of platelet integrin alpha IIb beta 3, the fibrinogen receptor". Proceedings of the Society for Experimental Biology and Medicine. 208 (4): 346–60. doi:10.3181/00379727-208-43863a. PMID 7535429.
  3. Shattil SJ (August 1999). "Signaling through platelet integrin alpha IIb beta 3: inside-out, outside-in, and sideways". Thrombosis and Haemostasis. 82 (2): 318–25. PMID 10605720.
  4. Bellucci S, Caen J (September 2002). "Molecular basis of Glanzmann's Thrombasthenia and current strategies in treatment". Blood Reviews. 16 (3): 193–202. doi:10.1016/S0268-960X(02)00030-9. PMID 12163005.
  5. McMillan R (October 2007). "The pathogenesis of chronic immune thrombocytopenic purpura". Seminars in Hematology. 44 (4 Suppl 5): S3–S11. doi:10.1053/j.seminhematol.2007.11.002. PMID 18096470.


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