ABSTRACT

Purified protein 4.1 binds with 50-fold higher affinity to protein 4.1 depleted normal red cell membranes than to protein 4.1 depleted red cell membranes of Leach phenotype which lack Glycophorin C (GPC) and Glycophorin D (GPD). Experiments using purified protein 4.1 and p55 together with synthetic peptides corresponding to different regions of the cytoplasmic domain of Glycophorins C and D (GPC/D) demonstrate that protein 4.1 interacts directly with GPC through residues 82-98. They also show that p55 binds to GPC through residues 112-128. Since p55 also binds directly to protein 4.1 it is clear that protein 4.1 can bind to GPC through two different sites either directly through residues 82-98 or indirectly through p55. These results show that GPC and GPD provide major attachment sites for the red cell skeleton via protein 4.1 and that p55 is part of this complex.