glycoprotein Ib

{{Short description|Protein found in platelets}}

File:Protein_GP1BA_PDB_1gwb.png

Glycoprotein Ib (GPIb), also known as CD42,{{cite journal | vauthors = Bode AP, Read MS, Reddick RL | title = Activation and adherence of lyophilized human platelets on canine vessel strips in the Baumgartner perfusion chamber | journal = The Journal of Laboratory and Clinical Medicine | volume = 133 | issue = 2 | pages = 200–211 | date = February 1999 | pmid = 9989772 | doi = 10.1016/S0022-2143(99)90013-6 }}

is a component of the GPIb-V-IX complex on platelets. The GPIb-V-IX complex binds von Willebrand factor, allowing platelet adhesion and platelet plug formation at sites of vascular injury. Glycoprotein Ibα (GPIbα) is the major ligand-binding subunit of the GPIb-V-IX complex. GPIbα is heavily glycosylated.{{cite journal | vauthors = Hollenhorst MA, Tiemeyer KH, Mahoney KE, Aoki K, Ishihara M, Lowery SC, Rangel-Angarita V, Bertozzi CR, Malaker SA | display-authors = 6 | title = Comprehensive analysis of platelet glycoprotein Ibα ectodomain glycosylation | journal = Journal of Thrombosis and Haemostasis | volume = 21 | issue = 4 | pages = 995–1009 | date = April 2023 | pmid = 36740532 | pmc = 10065957 | doi = 10.1016/j.jtha.2023.01.009 }}

It is deficient in the Bernard–Soulier syndrome. A gain-of-function mutation causes platelet-type von Willebrand disease.{{cite book | vauthors = McPherson RA, Pincus MR |title=Henry's Clinical Diagnosis and Management by Laboratory Methods |date=2007 |publisher=Saunders Elsevier |location=Philadelphia, Pa |isbn=978-1-4160-0287-1 |edition=21st | pages = 760–762}}

Autoantibodies against Ib/IX can be produced in immune thrombocytopenic purpura.{{cite journal | vauthors = McMillan R | title = The pathogenesis of chronic immune thrombocytopenic purpura | journal = Seminars in Hematology | volume = 44 | issue = 4 Suppl 5 | pages = S3–S11 | date = October 2007 | pmid = 18096470 | doi = 10.1053/j.seminhematol.2007.11.002 }}

Components include GP1BA and GP1BB.

It complexes with Glycoprotein IX.