Alterations in membrane protein and phosphorylation pattern in beta-thalassemic red blood cells

The architecture and phosphorylation pattern of RBC membranes were studied in intact RBC and ghosts of patients with beta-thalassemia intermedia. Electron microscopic studies showed severe morphological alterations in ghosts from spx thalassemic patients. The polypeptide pattern obtained on SDS-PAGE revealed a fourfold increase in globin content of ghosts from spx patients. In addition, multiple protein bands were detected migrating below band 4.2, accompanied by alterations in the band 3 zone. When membrane protein phosphorylation was examined by SDS-PAGE and auto-radiography following incubation of intact RBC with [32P]Pi, a reduced labeling of the normally phosphorylated polypeptides was found in the thalassemic RBC. In addition, new phosphorylated peptides appeared in the region of band 3 and below band 4. On the other hand, phosphorylation of isolated membranes with [gamma-32P]ATP showed no major differences in the labeling of the major phosphorylated proteins. An analysis of the initial rate of spectrin-band 2.1 phosphorylation obtained by counting the excised bands from the SDS gels showed that there was a twofold increase in spectrin-band 2.1-phosphorylation rate catalyzed by cAMP-dependent protein-kinase in the thalassemic ghosts, although no differences were found in the extent of spectrin phosphorability. The results are consistent with major changes in membrane protein disposition in thalassemic RBC, most probably caused by the precipitation of excess globin chains.