Islet transplantation is an emerging treatment option for type 1 diabetes but its application is limited by the shortage of human pancreas donors. Characterization of the N- and O-glycan surface ...antigens that vary between human and genetically engineered porcine islet donors could shed light on targets of antibody mediated rejection.
N- and O-glycans were isolated from human and adult porcine islets and analyzed using matrix-assisted laser-desorption time-of-flight mass spectrometry (MALDI-TOF-MS) and electrospray ionization mass spectrometry (ESI-MS/MS).
A total of 57 porcine and 34 human N-glycans and 21 porcine and 14 human O-glycans were detected from cultured islets. Twenty-eight of which were detected only from porcine islets, which include novel xenoantigens such as high-mannose type N-glycans with core fucosylation and complex-type N-glycans with terminal neuraminic acid residues. Porcine islets have terminal N-glycolylneuraminic acid (NeuGc) residue in bi-antennary N-glycans and sialyl-Tn O-glycans. No galactose-α-1,3-galactose (α-Gal) or Sda epitope were detected on any of the islets.
These results provide important insights into the potential antigenic differences of N- and O-glycan profiles between human and porcine islets. Glycan differences may identify novel gene targets for genetic engineering to generate superior porcine islet donors.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Despite the fundamental roles of sialyl- and fucosyltransferases in mammalian physiology, there are few pharmacological tools to manipulate their function in a cellular setting. Although fluorinated ...analogs of the donor substrates are well-established transition state inhibitors of these enzymes, they are not membrane permeable. By exploiting promiscuous monosaccharide salvage pathways, we show that fluorinated analogs of sialic acid and fucose can be taken up and metabolized to the desired donor substrate-based inhibitors inside the cell. Because of the existence of metabolic feedback loops, they also act to prevent the de novo synthesis of the natural substrates, resulting in a global, family-wide shutdown of sialyl- and/or fucosyltransferases and remodeling of cell-surface glycans. As an example of the functional consequences, the inhibitors substantially reduce expression of the sialylated and fucosylated ligand sialyl Lewis X on myeloid cells, resulting in loss of selectin binding and impaired leukocyte rolling.
Most platelet membrane proteins are modified by mucin-type core 1-derived glycans (O-glycans). However, the biological importance of O-glycans in platelet clearance is unclear. Here, we generated ...mice with a hematopoietic cell-specific loss of O-glycans (HC C1galt1
−/−). These mice lack O-glycans on platelets and exhibit reduced peripheral platelet numbers. Platelets from HC C1galt1
−/− mice show reduced levels of α-2,3-linked sialic acids and increased accumulation in the liver relative to wild-type platelets. The preferential accumulation of HC C1galt1
−/− platelets in the liver was reduced in mice lacking the hepatic asialoglycoprotein receptor Ashwell–Morell receptor (AMR). However, we found that Kupffer cells are the primary cells phagocytosing HC C1galt1
−/− platelets in the liver. Our results demonstrate that hepatic AMR promotes preferential adherence to and phagocytosis of desialylated and/or HC C1galt1
−/− platelets by the Kupffer cell through its C-type lectin receptor CLEC4F. These findings provide insights into an essential role for core 1 O-glycosylation of platelets in their clearance in the liver.
Many pathogenic bacteria, including Streptococcus gordonii, possess a pathway for the cellular export of a single serine-rich-repeat protein that mediates the adhesion of bacteria to host cells and ...the extracellular matrix. This adhesin protein is O-glycosylated by several cytosolic glycosyltransferases and requires three accessory Sec proteins (Asp1–3) for export, but how the adhesin protein is processed for export is not well understood. Here, we report that the S. gordonii adhesin GspB is sequentially O-glycosylated by three enzymes (GtfA/B, Nss, and Gly) that attach N-acetylglucosamine and glucose to Ser/Thr residues. We also found that modified GspB is transferred from the last glycosyltransferase to the Asp1/2/3 complex. Crystal structures revealed that both Asp1 and Asp3 are related to carbohydrate-binding proteins, suggesting that they interact with carbohydrates and bind glycosylated adhesin, a notion that was supported by further analyses. We further observed that Asp1 also has an affinity for phospholipids, which is attenuated by Asp2. In summary, our findings support a model in which the GspB adhesin is sequentially glycosylated by GtfA/B, Nss, and Gly and then transferred to the Asp1/2/3 complex in which Asp1 mediates the interaction of the Asp1/2/3 complex with the lipid bilayer for targeting of matured GspB to the export machinery.
Cigarette smoking plays a major role in cardiovascular diseases. The acute effects of cigarette smoking produce central nervous system-mediated activation of the sympathetic nervous system. The ...overactive sympathetic nervous system stimulates the secretion of serotonin (5-HT) and catecholamine into blood at supraphysiological levels. The correlation between these pathological conditions induced by smoking and the increased risk of thrombosis has not been thoroughly investigated. The goal of our study was to explore cigarette smoking-associated changes in platelet biology mediated by elevated 5-HT and catecholamine levels in blood plasma.
Using blood samples collected from healthy nonsmokers and smokers (15 minutes after smoking), we determined that cigarette smoking increased the plasma 5-HT/catecholamine concentration by several fold and the percent aggregation of platelets 2-fold. Liquid chromatography-tandem mass spectrometry analysis of proteins eluted from platelet plasma membranes of smokers and nonsmokers demonstrated that GTPase-activating proteins and proteins participating in the actin cytoskeletal network were differentially and significantly elevated in smokers' platelet membranes compared with those of nonsmokers. Interestingly, Matrix-assisted laser desorption/ionization-mass spectrometry analyses of the glycans eluted from platelet plasma membranes of the smokers demonstrated that the level and structures of glycans are different from the nonsmokers' platelet surface glycans. Pharmacological blockade of 5-HT or catecholamine receptors counteracted the 5-HT/catecholamine-mediated aggregation and altered the level and composition of glycan on platelet surfaces.
Based on our findings, we propose that smoking-associated 5-HT/catecholamine signaling accelerates the trafficking dynamics of platelets, and this remodels the surface proteins and glycans and predisposes platelets to hyperactive levels. Smokers' platelets also had correspondingly higher resting concentrations of intracellular calcium and transglutaminase activity. These findings suggest a link among smoking, platelet 5-HT, catecholamine signaling, and their downstream effectors-including phospholipase C and inositol-1,4,5-triphosphate pathways-resulting in an increased tonic level of platelet activation in smokers.
Microbial interaction with the host through sensing receptors, including SIGNR1, sustains intestinal homeostasis against pathogenic inflammation. The newly discovered commensal Propionibacterium ...strain, P. UF1, regulates the intestinal immunity against pathogen challenge. However, the molecular events driving intestinal phagocytic cell response, including colonic dendritic cells (DCs), by this bacterium are still elusive. Here, we demonstrate that the glycosylation of bacterial large surface layer protein A (LspA) by protein O-mannosyltransferase 1 (Pmt1) regulates the interaction with SIGNR1, resulting in the control of DC transcriptomic and metabolomic machineries. Programmed DCs promote protective T cell response to intestinal Listeria infection and resist chemically induced colitis in mice. Thus, our findings may highlight a novel molecular mechanism by which commensal surface glycosylation interacting with SIGNR1 directs the intestinal homeostasis to potentially protect the host against proinflammatory signals inducing colonic tissue damage.
Congenital disorder of glycosylation (PMM2-CDG) results from mutations in pmm2, which encodes the phosphomannomutase (Pmm) that converts mannose-6-phosphate (M6P) to mannose-1-phosphate (M1P). ...Patients have wide-spectrum clinical abnormalities associated with impaired protein N-glycosylation. Although it has been widely proposed that Pmm2 deficiency depletes M1P, a precursor of GDP-mannose, and consequently suppresses lipid-linked oligosaccharide (LLO) levels needed for N-glycosylation, these deficiencies have not been demonstrated in patients or any animal model. Here we report a morpholino-based PMM2-CDG model in zebrafish. Morphant embryos had developmental abnormalities consistent with PMM2-CDG patients, including craniofacial defects and impaired motility associated with altered motor neurogenesis within the spinal cord. Significantly, global N-linked glycosylation and LLO levels were reduced in pmm2 morphants. Although M1P and GDP-mannose were below reliable detection/quantification limits, Pmm2 depletion unexpectedly caused accumulation of M6P, shown earlier to promote LLO cleavage in vitro. In pmm2 morphants, the free glycan by-products of LLO cleavage increased nearly twofold. Suppression of the M6P-synthesizing enzyme mannose phosphate isomerase within the pmm2 background normalized M6P levels and certain aspects of the craniofacial phenotype and abrogated pmm2-dependent LLO cleavage. In summary, we report the first zebrafish model of PMM2-CDG and uncover novel cellular insights not possible with other systems, including an M6P accumulation mechanism for underglycosylation.
•DFG-5 α-1,6-mannase associates with cell wall glycoproteins. This association is dependent upon N-linked galactomannans.•DFG-5 recognizes the α-1,6-backbone of the N-linked galactomannans and has ...enzymatic activity.•DFG-5 discriminates between cell wall glycoproteins and secreted glycoproteins.•By cleaving the N-linked galactomannans on cell wall glycoproteins, DFG-5 targets them for incorporation into the cell wall.•Secreted glycoproteins are not recognized by DFG-5 and are released into the growth medium.
The formation of a cell wall is vital for the survival and growth of a fungal cell. Fungi express members of the GH76 family of α-1,6-mannanases which play an important role in cell wall biogenesis. In this report we characterize the Neurospora crassa DFG-5 α-1,6-mannanase and demonstrate that it binds to the α-1,6-mannose backbone of an N-linked galactomannan found on cell wall glycoproteins. We show that DFG-5 has an enzymatic activity and provide evidence that it processes the α-1,6-mannose backbone of the N-linked galactomannan. Site-directed mutagenesis and complementation experiments show that D116 and D117 are located at the DFG-5 active site. D76 and E130, which are located in a groove on the opposite side of the protein, are also important for enzyme function. Cell wall glycoproteins co-purify with DFG-5 demonstrating a specific association between DFG-5 and cell wall glycoproteins. DFG-5 is able to discriminate between cell wall and secreted glycoproteins, and does not bind to the N-linked galactomannans present on secreted glycoproteins. DFG-5 plays a key role in targeting extracellular glycoproteins to their final destinations. By processing the galactomannans on cell wall proteins, DFG-5 targets them for cell wall incorporation by lichenin transferases. The N-linked galactomannans on secreted proteins are not processed by DFG-5, which targets these proteins for release into the extracellular medium.
Many pathogenic bacteria, including Streptococcus gordonii, possess a pathway for the cellular export of a single serine-rich-repeat protein that mediates the adhesion of bacteria to host cells and ...the extracellular matrix. This adhesin protein is O-glycosylated by several cytosolic glycosyltransferases and requires three accessory Sec proteins (Asp1–3) for export, but how the adhesin protein is processed for export is not well understood. Here, in this paper, we report that the S. gordonii adhesin GspB is sequentially O-glycosylated by three enzymes (GtfA/B, Nss, and Gly) that attach N-acetylglucosamine and glucose to Ser/Thr residues. We also found that modified GspB is transferred from the last glycosyltransferase to the Asp1/2/3 complex. Crystal structures revealed that both Asp1 and Asp3 are related to carbohydrate-binding proteins, suggesting that they interact with carbohydrates and bind glycosylated adhesin, a notion that was supported by further analyses. We further observed that Asp1 also has an affinity for phospholipids, which is attenuated by Asp2. In summary, our findings support a model in which the GspB adhesin is sequentially glycosylated by GtfA/B, Nss, and Gly and then transferred to the Asp1/2/3 complex in which Asp1 mediates the interaction of the Asp1/2/3 complex with the lipid bilayer for targeting of matured GspB to the export machinery.
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