Glycophorins A (GPA) and B (GPB) are single pass membrane sialoglycoproteins. GPA and GPB provide the cells with a large mucin like surface, which maybe provides a barrier to cell fusion. Glycophorin A is the major intrinsic membrane protein of the erythrocyte. The N-terminal glycosylated segment, which lies outside the erythrocyte membrane, has MN blood group receptors and also binds influenza virus.