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Site-specific profiling of structure and function of IgM B cell receptor glycans

ABSTRACT: Although N-linked glycans play pivotal roles in the regulation of antibody effector functions, little is known about the composition and functional impact of glycans expressed by human B cell receptors (BCRs), likely due to technical challenges. Here, we describe the site-specific glycosylation profiles of all four N-linked glycosylation-sites of human IgM BCRs from primary naive and memory B cells. We show that the BCR glycans have not undergone structural changes during the transition from naive to memory cells. Moreover, using B cell lines expressing well-defined BCRs, we show that individual glycosylation sites are non-essential for cell-surface expression, and that the absence of the IgM BCR N209 glycan reduces the antigen-binding capacity of B cells. Collectively, these findings shows high conservation of IgM BCR glycosylation across IgM BCR B cell subsets and indicate a limited contribution to BCR expression and function, suggesting BCR glycans may have evolved to support IgM antibody functions.

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ORGANISM(S): Homo Sapiens (human)

TISSUE(S): B Cell, Cell Culture, Blood

SUBMITTER: Rayman Tjokrodirijo

LAB HEAD: Peter A. van Veelen

PROVIDER: PXD062559 | Pride | 2025-12-09

REPOSITORIES: Pride

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Project description:Majority of B cell malignancies originate in the germinal centers (GCs), where B cells undergo activation to mutationally diversify their antibody genes and switch from the default Immunoglobulin M (IgM) or IgD B cell receptor (BCR) to IgG, IgA or IgE BCR isotypes. Similar to normal B cells, malignant B cells rely on signals emanating from the BCR for their survival and growth. While studies have primarily focused on elucidating the functions of IgM-mediated signaling in lymphoma pathogenesis, GC-derived lymphomas also express IgG and IgA BCR isotypes that greatly differ from IgM in their signaling potential. How these distinct non-IgM BCRs contribute to the pathogenesis of B cell malignancies is not well understood. Interestingly, B cell lymphoma patients expressing IgG BCR isotypes show better prognosis and survival than those expressing IgM BCR isotype. Consistent with this, we show that Diffuse Large B Cell Lymphoma (DLBCL) patients with higher IgG1 expression are associated with lower stages of disease than those with higher IgM expression. To directly test the roles of distinct BCR isotypes, we developed isogenic lymphoma cells that either express IgM or IgG1 BCRs. Interestingly, the IgG1-switched lymphoma cells fail to form tumors in mice whereas their IgM counterparts establish aggressive tumors. Moreover, co-transplantation of IgG1 and IgM expressing human and mouse lymphoma cells leads to emergence of tumors expressing IgM (and not IgG1), demonstrating that IgM BCRs are strongly favored over IgG1. Mechanistically, IgG1 expressing lymphoma cells and non-malignant activated B cells have reduced survival which is associated with a dysfunctional mitochondrial state triggered by stronger calcium responses in IgG1 in comparison to IgM cells. Genetic reversal of IgG1 to IgM or pharmacological dampening of the calcium signaling is sufficient to correct the mitochondrial defects and rescue the survival of IgG1 B cells. Our findings demonstrate that distinct BCR isotypes are inherently unique in their activities and can differentially impact B cell lymphoma pathogenesis.

Project description:Human noroviruses, globally the main cause of viral gastroenteritis, show strain specific affinity for histo-blood group antigens (HBGA) and can successfully be propagated ex vivo in human intestinal enteroids (HIEs). HIEs established from jejunal stem cells of individuals with different ABO, Lewis and secretor geno- and phenotypes, show varying susceptibility to such infections. Using bottom-up glycoproteomic approaches we have defined and compared the N-linked glycans of glycoproteins of seven jejunal HIEs. Membrane proteins were extracted, trypsin digested, and glycopeptides enriched by hydrophilic interaction liquid chromatography and analyzed by nanoLC-MS/MS. The Byonic software was used for glycopeptide identification followed by hands-on verifications and interpretations. Glycan structures and attachment sites were identified from MS 2 spectra obtained by higher-energy collision dissociation through analysis of diagnostic saccharide oxonium ions (B-ions), stepwise glycosidic fragmentation of the glycans (Y-ions), and peptide sequence ions (b- and y-ions). Altogether 694 unique glycopeptides from 93 glycoproteins were identified. The N-glycans encompassed pauci- and oligomannose, hybrid- and complex-type structures. Notably, polyfucosylated HBGA-containing glycopeptides of the four glycoproteins tetraspanin-8, carcinoembryonic antigen-related cell adhesion molecule 5, sucrose-isomaltase and aminopeptidase N were especially prominent and were characterized in detail and related to donor ABO, Lewis and secretor types of each HIE. Virtually no sialylated N-glycans were identified for these glycoproteins suggesting that terminal sialylation was infrequent compared to fucosylation and HBGA biosynthesis. This approach gives unique site-specific information on the structural complexity of N-linked glycans of glycoproteins of human HIEs and provides a platform for future studies on the role of host glycoproteins in gastrointestinal infectious diseases.

			Action	DRS
	Byonic_result_files.zip	Other
	E20232000259a.raw	Raw
	E20232000260a.raw	Raw
	E20232000261a.raw	Raw
	E20232000262a.raw	Raw

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Site-specific profiling of structure and function of IgM B cell receptor glycans

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