CD42c GPIbβ (platelet glycosylation)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Lineage Restricted Molecule
Type 1 glycoprotein
Platelet
Megakaryocyte
Endothelium
Brain
Heart
24 / 24
160 / 160

Expression
CD42c is expressed and restricted on platelets and megakaryocytes.  Red blood cells, granulocytes, T cells and thymocytes do not express CD42c.  The CD42 complex is a major component of the platelet surface with 25,000 copies per platelet.  CD42c is also expressed in non-hematopoietic tissues such as endothelium, brain and heart.

Structure
MOLECULAR FAMILY NAME: Belongs to the mucin family.

CD42c is a β chain single-pass type-1 181 aa glycoprotein.  It contains an 122 aa extracellular domain which contains 1 24 aa tandem leucine-rich sequence flanked by 22 aa consensus sequences, 1 potential N-glycosylation site and 1 phosphorylation site at Ser166, a 25 aa transmembrane domain which participates in signaling through phosphorylation of its intracellular domain and and a 34 aa cytoplasmic domain.   CD42c belongs to the mucin family which is part of the leucine-rich repeat family.  CD42c forms a disulfide-linked heterodimer with an a chain CD42b and a b chain CD42c.  It forms a non-covalent linked complex with CD42a.  Unlike CD42b, which is rich in O-linked oligosaccharides, CD42c has only N-linked chains of the lactosamine type.

MOLECULAR MASS
Cell Type Unreduced Reduced Comment
Platelets 160 kDa 24 kDa (+145, CD42b [GPIba])

POST-TRANSCRIPTIONAL MODIFICATION

A 411 aa protein arising from a longer, unspliced transcript in endothelial cells has been described, however, the authenticity of this product has been questioned.

POST-TRANSLATIONAL MODIFICATION

There is 1 potential N-glycosylation site.  Acylation, primarily palmitoylation, of GPIb has been found.  There is a phosphorylation site at Ser166, which can be phosphorylated by cAMP dependent protein kinase.

Ligands
CD42c complex binds von Willebrand factor and thrombin.

LIGANDS AND MOLECULES ASSOCIATED WITH CD42c
Molecule Comment
CD42a CD42c is non-covalently linked with CD42a
CD42b CD42c forms a disulfide-linked heterodimer with CD42b
CD42d CD42c is non-covalently linked with CD42d



Function
CD42c combines with CD42b, CD42a and CD42d to form a complex which functions as a receptor for von Willebrand factor.  The complex mediates adhesion of platelets to subendothelial matrics, which are exposed upon damage to the endothelium, at high shear rates.  It also amplifies the platelet response to thrombin during platelet activation where thrombin is involved.  Phosphorylation of the Ser-166 in CD42c may regulate cytoskeleton interactions in platelets.

BIOCHEMICAL ACTIVITY

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

DISEASE RELEVANCE AND FUNCTION OF CD42c IN INTACT ANIMAL

Mutations of CD42c gives rise to Bernard-Soulier syndrome (BSS) which is a bleeding disorder with the presence of giant platelets and is characterized by the absence of the GPIb/IX/V CD42a-d complex.  So far mutations have been found in the genes encoding CD42a, CD42b and CD42c in patients with BSS.

Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD42c
Molecule Comment
GATA-1
Ets

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD42c
Molecule Comment
cAMP dependent protein kinase


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 2812P13224
Antibodies

Revised June 25, 2008


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