• GPIba
• GPIbalpha
• Glycocalicin

MAJOR LINKS FOR CD42b  

• NCBI LocusLink Record: 2811
• Mendelian Inheritance in Man (OMIM): 231200
• SwissProt annotated protein record: P07359

• The CD42a-d-complex serves as receptor for von Willebrand factor (vWf) and thrombin
• The actual binding site for vWf and thrombin lies on CD42b (GPIbalpha)**

CELLULAR FUNCTION OF CD42b  

• The complex mediates adhesion of platelets to subendothelial matrices (exposed upon damage to the endothelium) at high shear rates
• The cytoplasmic region is associated via actin-binding protein (filamin) with the cytoskeleton**
• It also amplifies the platelet response to thrombin during platelet activation where thrombin is involved

DISEASE RELEVANCE OF CD42b AND FUNCTION OF CD42b IN INTACT ANIMAL  

• Absence of 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**
• Mutations in the double-loop region enhancing binding to von Willebrand factor have been found in Platelet-type (Pseudo) von Willebrand's disease, characterized by reduced plasma vWf high multimers but normal platelet multimers, and thrombocytopenia
• The CD42b carries a single amino-acid polymorphism (Met145Thr), resulting in the Ko (Syp, HPA-2) alloantigen system. CD42b mouse monoclonal antibodies (MoAbs) are used for detection of auto-and allo-platelet antibodies with the MAIPA assay**

• Families in which CD42b is a member
  • CD42b-->Mucins

MOLECULAR STRUCTURE OF CD42b  

• Heterodimer composed of an alpha chain (CD42b) and a beta chain (CD42c) linked by a disulfide bond. It forms a non-covalent linked complex with CD42a and d
• NH2-terminal extracellular region of approximately 481 amino acids, a transmembrane segment of approximately 29 amino acids and an intracellular region of 100 amino acids. The extracellular region contains seven tandem leucine-rich glycoprotein repeat sequences of 24 amino acids, flanked by consensus flanking sequences of 22 amino acids**
• There are two hydrophilic regions, one extensively O-glycosylated
• There are several polymorphisms including the Thr145-Met and a size polymorphism involving 1,2,3 or 4 copies of a 13 amino acid segment in the highly O-glycosylated region, each containing 5 putative O-glycosylation sites. The 4 repeat version is so far found exclusively in East Asian populations and the 3 repeat version in Caucasian**

MOLECULAR MASS OF CD42b  

POST-TRANSCRIPTIONAL MODIFICATION OF CD42b   - No information

POST-TRANSLATIONAL MODIFICATION OF CD42b  

• There are four potential N-glycosylation sites and many (approximately 43) O-glycosylation sites
• Acylation, primarily palmitoylation, of GPIb has been found
• Three tyrosine residues (Tyr276, 278 & 279) are sulfated

SUBSTRATES FOR CD42b   - No information

ENZYMES WHICH MODIFY CD42b  

LIGANDS FOR CD42b AND MOLECULES ASSOCIATED WITH CD42b  

• Expression restricted to platelets and megakaryocytes

SELECTION OF OTHER CD42b-SPECIFIC REFERENCE MAB  

REVIEWS

PRIMARY CITATIONS

1. Clemetson KJ,McGregor JL,James E,Dechavanne M,Luscher EF Characterization of the platelet membrane glycoprotein abnormalities in Bernard-Soulier syndrome and comparison with normal by surface-labeling techniques and high-resolution two-dimensional gel electrophoresis. J Clin Invest 1982 70:304 PubMed

2. Fox JE,Aggerbeck LP,Berndt MC Structure of the glycoprotein Ib.IX complex from platelet membranes. J Biol Chem 1988 263:4882 PubMed

3. Kuijpers RW,Ouwehand WH,Bleeker PM,Christie D,von dem Borne AE Localization of the platelet-specific HPA-2 (Ko) alloantigens on the N- terminal globular fragment of platelet glycoprotein Ib alpha. Blood 1992 79:283 PubMed

4. Lopez JA,Chung DW,Fujikawa K,Hagen FS,Papayannopoulou T,Roth GJ Cloning of the alpha chain of human platelet glycoprotein Ib: a transmembrane protein with homology to leucine-rich alpha 2- glycoprotein. Proc Natl Acad Sci U S A 1987 84:5615 PubMed

5. Miller JL,Castella A Platelet-type von Willebrand's disease: characterization of a new bleeding disorder. Blood 1982 60:790 PubMed

6. Muszbek L,Laposata M Glycoprotein Ib and glycoprotein IX in human platelets are acylated with palmitic acid through thioester linkages. J Biol Chem 1989 264:9716 PubMed

7. Nurden AT,Dupuis D,Kunicki TJ,Caen JP Analysis of the glycoprotein and protein composition of Bernard-Soulier platelets by single and two-dimensional sodium dodecyl sulfate- polyacrylamide gel electrophoresis. J Clin Invest 1981 67:1431 PubMed

8. Schick PK,Walker J The acylation of megakaryocyte proteins: glycoprotein IX is primarily myristoylated while glycoprotein Ib is palmitoylated. Blood 1996 87:1377 PubMed

9. Weiss HJ,Meyer D,Rabinowitz R,Pietu G,Girma JP,Vicic WJ,Rogers J Pseudo-von Willebrand's disease. An intrinsic platelet defect with aggregation by unmodified human factor VIII/von Willebrand factor and enhanced adsorption of its high-molecular-weight multimers. N Engl J Med 1982 306:326 PubMed

WWW RESOURCES

Portions copyright by Garland Press and by the International Workshops on Human Leukocyte Differentiation Antigens; used with permission

Modified 10/14/99   mpr@mail.nih.gov