Topology and organization of human Rh (rhesus) blood group-related polypeptides

The Rh blood group antigens are associated with nonglycosylated human erythrocyte membrane proteins of molecular mass 30 kDa (the Rh30 polypeptides) and a glycoprotein of 40-100 kDa (the Rh glycoprotein). We have studied the topology of this family of proteins in the erythrocyte membrane. We confirmed the predicted cytosolic localization of the C and N termini of the Rh protein family. We located Lys-196 and Arg-323 of the Rh glycoprotein to the cytosol, and Glu-34 to the extracellular side of the plasma membrane in erythrocytes, by N-terminal sequencing of Rh glycoprotein peptides produced by proteolysis at the cytoplasmic or extracellular side of the membrane. We also show that a glycan chain is present on only one (Asn-37) of the three potential N-glycan addition sites in the Rh glycoprotein. Studies of the Rh glycoprotein fragments that co-immunoprecipitated with the Rh30 polypeptides suggest there is an interaction between the Rh30 polypeptides and amino acids 35-196 of the Rh glycoprotein. A model for the organization of the components of the Rh complex in the red cell membrane is proposed.