GP-Ib, a surface membrane protein of platelets, participates in the formation of platelet plugs by binding to the A1 domain of vWF, which is already bound to the subendothelium. Two GP-Ib beta are disulfide-linked to one GP-Ib alpha. GP-IX is complexed with the GP-Ib heterodimer via a non covalent linkage (PubMed:17008541, PubMed:2070794). Interacts with FLNB (PubMed:9651345). Interacts with FLNA (via filamin repeats 4, 9, 12, 17, 19, 21, and 23) (PubMed:19828450). (Microbial infection) Interacts with Staphylococcus aureus protein SSL5. Glycocalicin is the product of a proteolytic cleavage/shedding, catalyzed by ADAM17, which releases most of the extracellular domain. Binding sites for vWF and thrombin are in this part of the protein. Position 161 is associated with platelet-specific alloantigen Siba (PubMed:1586750). Siba(-) has Thr-161 and Siba(+) has Met-161 (PubMed:1586750). Siba is involved in neonatal alloimmune thrombocytopenia (NATP) (PubMed:1586750, PubMed:7632942). Polymorphisms arise from a variable number of tandem 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 (PubMed:1577776, PubMed:7632942). Allele D contains one repeat starting at position 415, allele C contains two repeats, allele B (shown here) contains three repeats and allele A contains four repeats (PubMed:1577776). Allele B is associated with susceptibility to nonarteritic anterior ischemic optic neuropathy (PubMed:1577776). Disease susceptibility is associated with variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Platelet activation apparently involves disruption of the macromolecular complex of GP-Ib with the platelet glycoprotein IX (GP-IX) and dissociation of GP-Ib from the actin-binding protein.