Biosynthesis and Processing of Platelet GPIIb-IIIa in Human Megal ryocytes
نویسندگان
چکیده
Platelet membrane glycoprotein IIb-IIIa forms a calcium-dependent heterodimer and constitutes the fibrinogen receptor on stimulated platelets. GPIIb is a two-chain protein containing disulfide-linked ~t and 13 subunits. GPIIIa is a single chain protein. These proteins are synthesized in the bone marrow by megakaryocytes, but the study of their synthesis has been hampered by the difficulty in obtaining enriched population of megakaryocytes in large numbers. To examine the biosynthesis and processing of GPWo-IIIa, purified human megakaryocytes were isolated from liquid cultures of cryopreserved lenkocytes stem cell concentrates from patients with chronic myelogenous leukemia. Immunoprecipitation of [35S]methionine pulse-chase-labeled cell extracts by antibodies specific for the tx or 13 subunits of GPIIb indicated that GPIIb was derived from a precursor of Mr 130,000 that contains the tx and 13 subunits. This precursor was converted to GPIIb with a half-life of 4-5 h. No precursor form of GPHIa was detected. The glycosylation of GPI~-I I Ia was examined in megakaryocytes by metabolic labeling in the presence of tunicamycin, monensin, or treatment with endoglycosidase H. The polypeptide backbones of the GPIIb and the GPIIIa have molecular masses of 120 and 90 kD, respectively. High-mannose oligosaccharides are added to these polypeptide backbones co-translationally. The GPIIb precursor is then processed with conversion of highmannose to complex type carbohydrates yielding the mature subunits GPIIb0t (M~ 116,000) and GPI]bl3 (Mr 25,000). No posttranslational processing of GPRIa was
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Biosynthesis and processing of platelet GPIIb-IIIa in human megakaryocytes
Platelet membrane glycoprotein IIb-IIIa forms a calcium-dependent heterodimer and constitutes the fibrinogen receptor on stimulated platelets. GPIIb is a two-chain protein containing disulfide-linked alpha and beta subunits. GPIIIa is a single chain protein. These proteins are synthesized in the bone marrow by megakaryocytes, but the study of their synthesis has been hampered by the difficulty ...
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The platelet membrane glycoproteins GPIIb and GPIIIa form a calcium-dependent heterodimer that functions as a receptor for adhesive proteins on stimulated platelets. In this study, we have investigated the kinetics of the assembly reaction that result in GPIIb-IIIa dimerization. Pulse-chase experiments analysis performed on human megakaryocytes obtained from liquid cultures of chronic myelogeno...
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Platelet GpIIb/IIIa is a member of the integrin family of structurally related adhesion receptors, and adhesive proteins, such as fibrinogen. Ligand binding requires platelet activation by an agonist to convert the receptor to a state where it is capable to bind the ligand. In addition to this a modification, induction of the surface expression and ligand-binding function of an additional pool ...
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