glycoprotein IX platelet
The GP9 gene provides instructions for making a protein called glycoprotein IX (GPIX). This protein is one piece (subunit) of a protein complex called GPIb-IX-V, which plays a role in blood clotting. GPIb-IX-V is found on the surface of small cell fragments called platelets, which circulate in blood and are an essential component of blood clots. The complex can attach (bind) to a protein called von Willebrand factor, fitting together like a lock and its key. Von Willebrand factor is found on the inside surface of blood vessels, particularly when there is an injury. Binding of the GPIb-IX-V complex to von Willebrand factor allows platelets to stick to the blood vessel wall at the site of the injury. These platelets form clots, plugging holes in the blood vessels to help stop bleeding.
To form the GPIb-IX-V complex, GPIX interacts with other protein subunits called GPIb-alpha, GPIb-beta, and GPV, each of which is produced from a different gene. GPIX is essential for assembly of the complex at the platelet surface and helps stabilize the complex once it is formed.
At least 28 GP9 gene mutations have been found to cause Bernard-Soulier syndrome, a condition characterized by a reduced number of platelets that are larger than normal (macrothrombocytopenia) and excessive bleeding. These mutations lead to production of an altered GPIX subunit that is likely broken down too soon or that cannot get to the platelet surface. Lack of this subunit on the surface of platelets prevents formation of the GPIb-IX-V complex. Without GPIb-IX-V, platelets cannot come together at the site of an injury to form a clot, leading to the bleeding problems associated with Bernard-Soulier syndrome.
- glycoprotein 9
- glycoprotein IX (platelet)
- platelet glycoprotein IX precursor