Glycoproteins of Platelet Membranes from Glanzmann's Thrombasthenia. A Comparison with Normal Using Carbohydrate-Specific or Protein-Specific Labelling Techniques and High-Resolution Two-Dimensional Gel Electrophoresis

Abstract

Platelets from Glanzmann's thrombasthenia patients and from normal donors were surface labelled by techniques specific for sugars (terminal sialic acid, penultimate galactose/N-acetylgalactosamine) and proteins (tyrosine-histidine residues). These labelled platelets were solubilized in sodium dodecyl sulphate and separated on a two-dimensional electrophoretic system [O'Farrell, P. H. (1975) J . Biol. Chem. 250,4007 -4021 ] first according to their isoelectric point (PI) and then according to their molecular weight. In addition, unlabelled sodiumdodecyl-sulphate-solubilized platelets were separated on a two-dimensional polyacrylamide gel and the glycoproteins were identified by binding of 12sI-labelled Lens culinaris lectin (specific for mannose and glucose). In one Glanzmann's thrombasthenia patient glycoproteins IIbAl and IIIaAl were absent and in two others lower amounts of two glycoproteins were found in positions similar or close to these two membrane glycoproteins. The terminal sialic acid moieties of major glycoproteins (IbAl, IbBl and IIIbAI) were more intensely labelled in Glanzmann's thrombasthenia than in normals and these glycoproteins had an altered PI. A glycoprotein tentatively designated as Ic/IIa(?) had an altered PI and was labelled more intensely in Glanzmann's thrombasthenia platelets than in normals. A number of low-molecular-weight glycoproteins (IVa, IVb, VII) and one highmolecular weight glycoprotein normally found in platelets of healthy donors were reproducibly not detected in Glanzmann's thrombasthenia platelets. These results obtained by a combination of highly sensitive techniques strongly indicate that in Glanzmann's throinbasthenia the absence or reduction of two major membrane glycoproteins (IIbA1, IIIaA1) is not the only defect but that there appears to be a profound perturbation of the platelet membrane surface.

Drosophila position-specific antigens resemble the vertebrate fibronectin-receptor family.

“…Gpl 10 has a tendency to dimerize, as was also observed for the platelet receptor 3 subunit, IHa (McGregor et al, 1981; J.J.Calvete, J.L.McGregor and J.Gonzalez-Rodrigues, submitted).…”

Reduced surface expression and binding of fibronectin by thrombin-stimulated thrombasthenic platelets.

“…In addition, the autosomal recessive pattern of inheritence of thrombasthenia and the frequency of a specific membrane glycoprotein deficiency in this disorder (16), suggest that this disease may represent a deletion in a specific platelet membrane protein. Nevertheless, other studies have suggested a more global defect in platelet membrane proteins (20), and these data point to a second functional molecular defect in these platelets as well.…”

A murine monoclonal antibody that completely blocks the binding of fibrinogen to platelets produces a thrombasthenic-like state in normal platelets and binds to glycoproteins IIb and/or IIIa.

“…As these patients' platelets are deficient in the membrane glycoproteins GPIIb and GPIIIa (16,17) and as there is evidence that these glycoproteins complex together in association with fibrinogen (18), the GPIIb/IIIa complex has been tentatively identified as the fibrinogen receptor. Controversy persists, however, since it has been reported that thrombasthenic platelets have abnormalities in other surface glycoproteins (19) and one group has proposed that thrombasthenic platelets do indeed have receptors for fibrinogen, but are unable to expose them in response to agonist activation (20).…”