Probing human white blood cells for a novel type of protein N-glycosylation (#022)
Mammalian asparagine (N)-glycosylation covers three well-established classes of high mannose, hybrid and complex type glycans expressed on membrane or secreted glycoproteins. We have recently proposed paucimannosylation (Fuc0-1Man1-3GlcNAc2) as an unconventional N-glycan class in human neutrophils [1,2]. Despite their suggested immuno-functions, the presence of these truncated N-glycoproteins in other white blood cells has received little attention. We here explore the expression of paucimannosylation across multiple white blood cell types involved in the innate and adaptive immune response. Utilising PGC-LC-MS/MS, the N-glycomes of neutrophils, lymphocytes, monocytes and platelets isolated from whole blood of a healthy individual were profiled. Existing glycome data of white blood cells from multiple donors deposited in the Consortium for Functional Glycomics repository were also reinterpreted for the existence of these novel structures. In both approaches, paucimannosidic N-glycans were found to be highly enriched in the granulocytes i.e. eosinophils and neutrophils relative to the other immune cells in the myeloid and lymphoid lineages. Paucimannosidic glycoproteins were confirmed in isolated neutrophils with immunofluorescence using paucimannose-recognising antibodies. Co-localisation of paucimannosidic epitopes with β-hexosaminidase A and myeloperoxidase yielded clues to their subcellular localisation in the azurophilic granules of the neutrophil. Collectively, this suggests that protein paucimannosylation is a granulocyte-enriched glycosylation feature arising from cell-specific mechanisms during granulopoiesis. This map of protein paucimannosylation in white blood cells is important to understand the immunological role(s) of this novel class of human glycoproteins.
- Thaysen-Andersen, M., Venkatakrishnan, V., Loke, I., Laurini, C., Diestel, S., Parker, B.L., Packer, N.H., 2015. Human Neutrophils Secrete Bioactive Paucimannosidic Proteins from Azurophilic Granules into Pathogen-Infected Sputum. Journal of Biological Chemistry 290 (14), 8789-8802.
- Loke, I., Packer, N.H., Thaysen-Andersen, M., 2015. Complementary LC-MS/MS-Based N-Glycan, N-Glycopeptide, and Intact N-Glycoprotein Profiling Reveals Unconventional Asn71-Glycosylation of Human Neutrophil Cathepsin G. Biomolecules 5 (3), 1832-1854.