Abstract
Polypeptide phosphorylation and sialylation of the glycan moieties contribute to the charge heterogeneity of the class I major histocompatibility complex glycoproteins. The present study demonstrates that a unique acidic modification unrelated to phosphorylation or glycosylation also affects the charge heterogeneity of the H2-Kk heavy chain of BW5147 lymphoma cells. In vitro cultivation of BW5147 cells results in changes in charge heterogeneity of the H2-Kk heavy chains due to the unique acidic modification. Sequential papain digestion of the 45 000 M r H2-Kk glycoprotein yields a 42 500 M r glycopolypeptide initially, followed by production of a 39 000 M r glycopolypeptide. Results from experiments designed to localize and characterize the novel acidic modification suggest that the modification resides in the segment of the H2-Kk polypeptide located between the two papain cleavage sites. This portion of the polypeptide consists of the transmembrane region and part of the cytoplasmic domain of the H2-Kk heavy chain. At steady state, 25% of the total cell surface H2-Kk possesses this modification. In addition, the modification is mutually exclusive with the phosphorylation of the H2-Kk heavy chain at Ser-333. The possible biological significance of the novel modification of class I antigens is discussed.
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Received: 27 May 1997 / Revised: 10 September 1997
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Balomenos, D., Poretz, R. An acidic modification of the cytoplasmic domain contributes to the charge heterogeneity of the MHC class I antigens. Immunogenetics 47, 381–389 (1998). https://doi.org/10.1007/s002510050373
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DOI: https://doi.org/10.1007/s002510050373