CD42a GP9 (glycoprotein 9), GPIX (platelet glycoprotein)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Lineage Restricted Molecule
Type 1 glycoprotein
Platelet
Megakaryocyte
17 / 17
22 / 22

Expression
CD42a expression is restricted on platelets and megakaryocytes. Red blood cells, granulocytes, T cells and thymocytes do not express CD42a.  The CD42a complex is a major component of the platelet surface with 25,000 copies per platelet.


Structure
MOLECULAR FAMILY NAME: Belongs to the mucin family.

CD42a is a single-pass type-1 165 aa glycoprotein.  It contains an 134 aa N-terminal extracellular domain which contains 1 24 aa leucine-rich repeat sequence flanked by 22 aa consensus flanking sequences and  a N-glycoyslation site that may be myristoylated, a 20 aa transmembrane domain and a 6 aa cytoplasmic domain.  The mucin family belongs to the leucine-rich repeat family.  CD42a is a small membrane glycoprotein found on the surface of human platelets.  CD42a forms a non-covalent linked complex with CD42ba, cb and d.   

MOLECULAR MASS
Cell Type Unreduced Reduced Comment
Platelets 22 kDa 17-22 kDa

POST-TRANSCRIPTIONAL MODIFICATION: No information.

POST-TRANSLATIONAL MODIFICATION

CD42a has 1 N-glycosylation site and the protein may be myristolated.

Ligands
CD42a binds to von Willebrand factor and thrombin.

LIGANDS AND MOLECULES ASSOCIATED WITH CD42a
Molecule Comment
CD42b Forms non-covalent complex with CD42a
CD42c Forms non-covalent complex with CD42a
CD42d Forms non-covalent complex with CD42a




Function
CD42a combines with CD42b, CD42c and CD42d to form the CD42 complex.  It functions as a receptor for von Willebrand factor and as a vWF-dependent adhesion receptor thus mediating adhesion of platelets at high sheer rates to vWF in the subendothelial matrices that are exposed when damage to the endothelium occurs.  When thrombin is present, the CD42 complex amplifies the response to thrombin during platelet activation.   

BIOCHEMICAL ACTIVITY

The CD42a-d complex serves as receptor for von Willebrand factor (vWf) and thrombin. 

DISEASE RELEVANCE AND FUNCTION OF CD42a IN INTACT ANIMAL

Mutations in the CD42 complex leads to the Bernard Soulier syndrome (BSS), which is a bleeding disorder characterized by thrombocytopenia and giant platelets.  So far, mutations have been found in the genes encoding CD42a, CD42b and CD42c in patients with BSS.  CD42a mouse monoclonal antibodies are used for the detection of auto-anti-platelet antibodies with the monoclonal antibody-specific immobilization of platelet antibodies (MAIPA).

Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD42a
 
Molecule Comment
GATA-1
Ets

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD42a: No information.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 2815P14770
Antibodies
ALMA.16   View Reactivity
GRP-P   View Reactivity

Revised June 25, 2008


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