Structural relationships between human erythrocyte sialoglycoproteins β and γ and abnormal sialoglycoproteins found in certain rare human erythrocyte variants lacking the Gerbich blood-group antigen(s)

1. The human erythrocyte membrane sialoglycoproteins β and γ are important for the maintenance of the discoid shape of the normal erythrocyte. In this paper we show that the human erythrocyte sialoglycoproteins β and γ (hereafter called β and γ) are structurally related. Rabbit antisera produced against purified β and β1 and rendered specific to the cytoplasmic portion of these proteins also react with the cytoplasmic portion of γ. Some human anti-Gerbich (Ge) sera react with the extracellular portion of both β and γ. This reactivity is shown to be directed towards a common epitope on β and γ. However, most anti-Ge sera do not react with β, but react with extracellular epitope only present on γ. 2. All individuals who lack the Ge antigens lack β and γ. In some cases abnormal sialoglycoproteins are present in the erythrocytes, and these are shown to be structurally related to β and γ. Rabbit antisera raised against the purified abnormal sialoglycoprotein from a Ge-negative erythrocyte type reacted with the cytoplasmic portion of both β and γ. 3. Unlike normal β and γ, the abnormal sialoglycoproteins found in Ge-negative erythrocytes migrate as a diffuse band on SDS/polyacrylamide-gel electrophoresis. Studies using endoglycosidases suggest that the diffuse nature of these bands results from carbohydrate heterogeneity and that the abnormal sialoglycoproteins contain N-glycosidically linked oligosaccharides with repeating lactosamine units. Such polylactosamine chains are not present on normal β or γ.