| Summary: | 博士 === 國立陽明大學 === 微生物及免疫學研究所 === 101 === Glycosylation is an important post-translational modification process that modulates the structure and function of proteins, but its effect on the properties of plasma cells is largely unclear. The B cell maturation antigen (BCMA), an essential membrane protein for maintaining the survival of plasma cells, was identified as a glycoprotein only modified by a single N-glycan at Asn42 by click reactions with sugar analogs, fucyne and ManNAcyne, coupled with mass spectrometry analysis. Because BCMA was considered as an unglycosylated protein before, we examined and validated this finding by glycosidase treatment and point mutation. Glycopeptide analysis also showed the high mannose type and terminal sialic- and fucose-capped complex type glycosylations on BCMA at Asn42 only. We then investigated whether this sole N-glycan regulates the function of BCMA. We found that N-glycans on BCMA is capped by α2-3 and α2-6 sialylation and removal of all sialic acid by sialidase on plasma cells further promoted the ligand-mediated protection. This effect is associated with the increased surface retention of BCMA, leading to its elevated level and increased ligand binding on cell surface. Besides, the whole N-glycans and the fucosylation, but not sialylation, confer better binding of BCMA with ligands in an in vitro binding assay combined with different glycosidases treatments. This effect is not due to incorrect protein folding because circular dichroism analysis showed that the secondary structure between intact BCMA and mutated or glycosidase-treated BCMA was indistinguishable. Therefore, our results demonstrate the importance of N-glycosylation on BCMA in the regulation of functions of plasma cells.
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