| Structural highlights
Disease
GP1BA_HUMAN Genetic variations in GP1BA may be a cause of susceptibility to non-arteritic anterior ischemic optic neuropathy (NAION) [MIM:258660. NAION is an ocular disease due to ischemic injury to the optic nerve. It usually affects the optic disk and leads to visual loss and optic disk swelling of a pallid nature. Visual loss is usually sudden, or over a few days at most and is usually permanent, with some recovery possibly occurring within the first weeks or months. Patients with small disks having smaller or non-existent cups have an anatomical predisposition for non-arteritic anterior ischemic optic neuropathy. As an ischemic episode evolves, the swelling compromises circulation, with a spiral of ischemia resulting in further neuronal damage.[1] Defects in GP1BA are a cause of Bernard-Soulier syndrome (BSS) [MIM:231200; also known as giant platelet disease (GPD). BSS patients have unusually large platelets and have a clinical bleeding tendency.[2] [3] [4] [5] [6] [7] Defects in GP1BA are the cause of benign mediterranean macrothrombocytopenia (BMM) [MIM:153670; also known as autosomal dominant benign Bernard-Soulier syndrome. BMM is characterized by mild or no clinical symptoms, normal platelet function, and normal megakaryocyte count.[8] Defects in GP1BA are the cause of pseudo-von Willebrand disease (VWDP) [MIM:177820. A bleeding disorder is caused by an increased affinity of GP-Ib for soluble vWF resulting in impaired hemostatic function due to the removal of vWF from the circulation.[9] [10] [11] [12]
Function
GP1BA_HUMAN 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.
Publication Abstract from PubMed
Ectodomain shedding of glycoprotein (GP) Ibalpha is thought to mediate the clearance of activated, aged or damaged platelets. A monoclonal antibody, 5G6, has been developed recently to specifically bind to the GPIbalpha shedding cleavage site and to inhibit its shedding. However, the molecular mechanism underlying antigen recognition and inhibitory specificity is not clear. To elucidate the structural basis for 5G6 binding to GPIbalpha, we determined the crystal structure of 5G6 Fab fragment in complex with its epitope peptide KL10 (GPIbalpha residues 461-470, KLRGVLQGHL), to 2.4-A resolution. Key residues in both 5G6 and KL10 were mutated to validate their effects in antibody binding by using isothermal titration calorimetry. The 5G6 Fab-KL10 peptide complex structure confirmed the direct association of 5G6 with its target GPIbalpha residues and elucidated the molecular basis underlying its binding specificity and high affinity. The similar binding properties of 5G6 Fab fragment to GPIbalpha on human platelets as those to KL10 suggests that such an interaction may not be affected by the plasma membrane or nearby GPIbbeta. This structural information may facilitate further antibody optimization and humanization.
Structural basis for the specific inhibition of glycoprotein Ibalpha shedding by an inhibitory antibody.,Tao Y, Zhang X, Liang X, Zang J, Mo X, Li R Sci Rep. 2016 Apr 22;6:24789. doi: 10.1038/srep24789. PMID:27102061[13]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Salomon O, Rosenberg N, Steinberg DM, Huna-Baron R, Moisseiev J, Dardik R, Goldan O, Kurtz S, Ifrah A, Seligsohn U. Nonarteritic anterior ischemic optic neuropathy is associated with a specific platelet polymorphism located on the glycoprotein Ibalpha gene. Ophthalmology. 2004 Jan;111(1):184-8. PMID:14711733 doi:10.1016/j.ophtha.2003.05.006
- ↑ Miller JL, Lyle VA, Cunningham D. Mutation of leucine-57 to phenylalanine in a platelet glycoprotein Ib alpha leucine tandem repeat occurring in patients with an autosomal dominant variant of Bernard-Soulier disease. Blood. 1992 Jan 15;79(2):439-46. PMID:1730088
- ↑ Ware J, Russell SR, Marchese P, Murata M, Mazzucato M, De Marco L, Ruggeri ZM. Point mutation in a leucine-rich repeat of platelet glycoprotein Ib alpha resulting in the Bernard-Soulier syndrome. J Clin Invest. 1993 Sep;92(3):1213-20. PMID:7690774 doi:http://dx.doi.org/10.1172/JCI116692
- ↑ Simsek S, Noris P, Lozano M, Pico M, von dem Borne AE, Ribera A, Gallardo D. Cys209 Ser mutation in the platelet membrane glycoprotein Ib alpha gene is associated with Bernard-Soulier syndrome. Br J Haematol. 1994 Dec;88(4):839-44. PMID:7819107
- ↑ de la Salle C, Baas MJ, Lanza F, Schwartz A, Hanau D, Chevalier J, Gachet C, Briquel ME, Cazenave JP. A three-base deletion removing a leucine residue in a leucine-rich repeat of platelet glycoprotein Ib alpha associated with a variant of Bernard-Soulier syndrome (Nancy I). Br J Haematol. 1995 Feb;89(2):386-96. PMID:7873390
- ↑ Kenny D, Jonsson OG, Morateck PA, Montgomery RR. Naturally occurring mutations in glycoprotein Ibalpha that result in defective ligand binding and synthesis of a truncated protein. Blood. 1998 Jul 1;92(1):175-83. PMID:9639514
- ↑ Koskela S, Partanen J, Salmi TT, Kekomaki R. Molecular characterization of two mutations in platelet glycoprotein (GP) Ib alpha in two Finnish Bernard-Soulier syndrome families. Eur J Haematol. 1999 Mar;62(3):160-8. PMID:10089893
- ↑ Savoia A, Balduini CL, Savino M, Noris P, Del Vecchio M, Perrotta S, Belletti S, Poggi, Iolascon A. Autosomal dominant macrothrombocytopenia in Italy is most frequently a type of heterozygous Bernard-Soulier syndrome. Blood. 2001 Mar 1;97(5):1330-5. PMID:11222377
- ↑ Matsubara Y, Murata M, Sugita K, Ikeda Y. Identification of a novel point mutation in platelet glycoprotein Ibalpha, Gly to Ser at residue 233, in a Japanese family with platelet-type von Willebrand disease. J Thromb Haemost. 2003 Oct;1(10):2198-205. PMID:14521605
- ↑ Miller JL, Cunningham D, Lyle VA, Finch CN. Mutation in the gene encoding the alpha chain of platelet glycoprotein Ib in platelet-type von Willebrand disease. Proc Natl Acad Sci U S A. 1991 Jun 1;88(11):4761-5. PMID:2052556
- ↑ Murata M, Russell SR, Ruggeri ZM, Ware J. Expression of the phenotypic abnormality of platelet-type von Willebrand disease in a recombinant glycoprotein Ib alpha fragment. J Clin Invest. 1993 May;91(5):2133-7. PMID:8486780 doi:http://dx.doi.org/10.1172/JCI116438
- ↑ Russell SD, Roth GJ. Pseudo-von Willebrand disease: a mutation in the platelet glycoprotein Ib alpha gene associated with a hyperactive surface receptor. Blood. 1993 Apr 1;81(7):1787-91. PMID:8384898
- ↑ Tao Y, Zhang X, Liang X, Zang J, Mo X, Li R. Structural basis for the specific inhibition of glycoprotein Ibalpha shedding by an inhibitory antibody. Sci Rep. 2016 Apr 22;6:24789. doi: 10.1038/srep24789. PMID:27102061 doi:http://dx.doi.org/10.1038/srep24789
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