Human red blood cell Wright antigens: A genetic and evolutionary perspective on glycophorin A band 3 interaction

The Wright (Wr(a)/Wr(b)) blood group polymorphism is defined by an allelic change (Lys658Glu) in the band 3 protein; nevertheless, the Wr(b) antigen apparently requires glycophorin A (GPA) for surface presentation. To gain insight into the structural basis for this protein-protein interaction and delineate its relationship with Wr(b) antigen expression, we investigated GPA and band 3 sequence polymorphisms occurring in rare humans and nonhuman primates. The lack of GPA or amino acid residues 59 through 71 of GPA results in the absence of Wr(b) from human red blood cells (RBCs) exhibiting the M(k)M(k), En(a-), or MiV phenotype. However, the SAT homozygous cells carried a Glu(658) form of band 3 and a hybrid glycophorin with the entire GPA extramembrane domain from residues 1 through 71, yet expressed no Wr(b) antigen. This finding suggests that formation of the Wr(b) antigenic structure is dependent on protein folding and that the transmembrane junction of GPA is important in maintaining the required conformation. Comparative analyses of GPA and band 3 homologues led to the identification in the interacting regions of conserved and dispensable amino acid residues that correlated with the Wr(b) positive or negative status on nonhuman primates. In particular, the chimpanzee RBCs cells expressed Wr(b) and the Glu(658) form of band 3, which is identical to humans, but their GPA contained the Gly rather than Arg residue at position 61. Taken together, the results suggest that (1) Arg(61) of GPA and the proposed Arg(61)-Glu(658) charge pair are not crucial for Wr(b) antigen exhibition and (2) the role of GPA for interaction with band 3, including Glu(658), probably involves a number of amino acid residues located in the alpha-helical region and transmembrane junction. (C) 1996 by The American Society of Hematology.