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 glycopruteins were identified by binding of ¹²⁵I-labelled Lens culinaris lectin (specific for mannose and glucose). In one Glanzmann's thrombasthenia patient glycoproteins IIbA1 and IIIaA1 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 (IbA1, IbB1 and IIIbA1) 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 thrombasthenia 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.