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)

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Abstract
1. The human erythrocyte membrane sialoglycoproteins .beta. and .gamma. are important for the maintenance of the discoid shape of the normal erythrocyte. In this paper we show that the human erythrocyte sialoglycoproteins .beta. and .gamma. (hereafter called .beta. and .gamma.) are structurally related. Rabbit antisera produced against purified .beta. and .beta.1 and rendered specific to the cytoplasmic portion of these proteins also react with the cytoplasmic portion of .gamma.. Some human anti-Gerbich (Ge) sera react with the extracellular portion of both .beta. and .gamma.. This reactivity is shown to be directed towards a common epitope on .beta. and .gamma.. However, most anti-Ge sera do not react with .beta., but react with an extracellular epitope only present on .gamma.. 2. All individuals who lack the Ge antigens lack .beta. and .gamma.. In some cases abnormal sialoglycoproteins are present in the erythrocytes, and these are shown to be structurally related to .beta. and .gamma.. Rabbit antisera raised against the purified abnormal sialoglycoprotein from a Ge-negative erythrocyte type reacted with the cytoplasmic portion of both .beta. and .gamma.. 3. Unlike normal .beta. and .gamma., 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 .beta. or .gamma.