The PDZ domain, also known as the GLGF repeat/DHR domain, is an approximately 90-amino
acid motif discovered in a recently identified family of
proteins termed MAGUKs (
membrane-associated guanylate kinase homologues). Sequence comparison analysis has since identified PDZ domains in over 50
proteins. Like SH2 and SH3 domains, the PDZ domains mediate specific
protein-
protein interactions, whose specificities appear to be dictated by the primary structure of the PDZ domain as well as its binding target. Using
recombinant fusion proteins and a blot overlay assay, we show that a single copy of the PDZ domain in human erythrocyte p55 binds to the carboxyl terminus of the cytoplasmic domain of human erythroid
glycophorin C. Deletion mutagenesis of 21
amino acids at the amino terminus of the p55 PDZ domain completely abrogates its binding activity for
glycophorin C. Using an
alanine scan and surface plasmon resonance technique, we identify residues in the cytoplasmic domain of
glycophorin C that are critical for its interaction with the PDZ domain. The recognition specificity of the p55 PDZ domain appears to be unique, since the three PDZ domains of hDlg (human lymphocyte homologue of the Drosophila discs large
tumor suppressor) do not bind the cytoplasmic domain of
glycophorin C. Taken together with our previous studies, these results complete the identification of interacting domains in the ternary complex between p55,
glycophorin C, and
protein 4.1. Implications of these findings are discussed in terms of binding specificity and the regulation of cytoskeleton-membrane interactions.