An acidic modification of the cytoplasmic domain contributes to the charge heterogeneity of the MHC class I antigens.
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 Mr H2-Kk glycoprotein yields a 42 500 Mr glycopolypeptide initially, followed by production of a 39 000 Mr 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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Department of Biochemistry and Microbiology, Rutgers University, P. O. Box 231, New Brunswick, NJ 08903-0231, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D018929:Cell Culture Techniques; D003593:Cytoplasm / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism; D006183:H-2 Antigens / Q000737:chemistry* / Q000378:metabolism*; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D009439:Neuraminidase / Q000378:metabolism; D010206:Papain / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D055672:Static Electricity; D013997:Time Factors; D014407:Tumor Cells, Cultured
D006023:Glycoproteins; D006183:H-2 Antigens; D007143:Immunoglobulin Heavy Chains; D010446:Peptide Fragments; D020033:Protein Isoforms; D010768:Phosphoserine; D009439:Neuraminidase; D010206:Papain; D019158:N-Acetylneuraminic Acid