CD42b; platelet glycoprotein Ib alpha chain; glycoprotein Ibalpha; GP-Ib alpha; GPIb-alpha; GPIbA; antigen CD42b-alpha; human platelet antigen 2; HPA-2 (GP1BA)

Function

• subunit of platelet glycoprotein 1B
• interacts with FLNB
• glycocalicin (approximately extracellular part), is cleaved by calpain during platelet lysis

Structure

• contains 6 LRR repeats (leucine-rich repeats)
• binding sites for von Willebrand factor & thrombin are in the amino-terminal part of the molecule

Compartment

membrane

Pathology

• allele B of is associated with susceptibility to nonarteritic anterior ischemic optic neuropathy
• defects in GP1BA are a cause of
  • Bernard-Soulier syndrome
  • benign Mediterranean macrothrombocytopenia
  • von Willebrand disease

Polymorphism

• associated with platelet-specific alloantigen Siba; Siba(-) has Thr-161 & Siba(+) has Met-161
• polymorphisms arise from a variable number of tandem repeats (NNTR) 13-amino acid repeats of S-E-P-A-P-S-P-T-T-P-E-P-T in the mucin-like macroglycopeptide (Pro/Thr-rich) domain
  • allele A contains four repeats starting at position 415
  • allele B contains three repeats
  • allele C contains two repeats
  • allele D contains one repeat

Laboratory

• HPA-2 type in blood

More general terms

• CD42
• leucine-rich repeat-containing protein (LRRC)
• phosphoprotein

More specific terms

• glycocalcin

Component of

• platelet glycoprotein 1b

Database

• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:2811
• OMIM: https://mirror.omim.org/entry/153670
• OMIM: https://mirror.omim.org/entry/177820
• OMIM: https://mirror.omim.org/entry/231200
• OMIM: https://mirror.omim.org/entry/258660
• OMIM: https://mirror.omim.org/entry/606672
• UniProt: http://www.uniprot.org/uniprot/P07359.html