Allotype-Specific Glycosylation and Cellular Localization of Human Leukocyte Antigen Class I Proteins

Presentation of antigens by human leukocyte antigen (HLA) complexes at the cell surface is a key process in the immune response. The alpha-chain, containing the peptide-binding groove, is one of the most polymorphic proteins in the proteome. All HLA class I alpha-chains carry a conserved N-glycosylation site, but little is known about its nature and function. Here, we report an in-depth characterization of N-glycosylation features of HLA class I molecules. We observe that different HLA-A alpha-chains carry similar glycosylation, distinctly different from the HLA-B, HLA-C, and HLA-F alpha-chains. Although HLA-A displays the broadest variety of glycan characteristics, HLA-B alpha-chains carry mostly mature glycans, and HLA-C and HLA-F alpha-chains carry predominantly high-mannose glycans. We expected these glycosylation features to be directly linked to cellular localization of the HLA complexes. Indeed, analyzing HLA class I complexes from crude plasma and inner membrane-enriched fractions confirmed that most HLA-B complexes can be found at the plasma membrane, while most HLA-C and HLA-F molecules reside in the endoplasmic reticulum and Golgi membrane, and HLA-A molecules are more equally distributed over these cellular compartments. This allotype-specific cellular distribution of HLA molecules should be taken into account when analyzing peptide antigen presentation by immunopeptidomics.

Automated summary

The study analyzed in depth the N-glycosylation features of HLA class I molecules, finding that HLA-A alpha-chains have distinct glycosylation patterns compared to HLA-B, HLA-C, and HLA-F. The cellular distribution of HLA molecules varies based on their glycosylation features, with HLA-B predominantly found at the plasma membrane, and HLA-C and HLA-F mainly located in the endoplasmic reticulum and Golgi membrane. The findings highlight the importance of considering allotype-specific cellular distribution when analyzing peptide antigen presentation in immunopeptidomics.