Unraveling the sequence of cytosolic reactions in the export of GspB adhesin from Streptococcus gordonii.

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.

High-mannose type N-glycans with core fucosylation and complex-type N-glycans with terminal neuraminic acid residues are unique to porcine islets.

OBJECTIVES: 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. METHODS: 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). RESULTS: 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. CONCLUSIONS: 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.

Cigarette Smoking-Associated Alterations in Serotonin/Adrenalin Signaling Pathways of Platelets.

BACKGROUND: 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. METHODS AND RESULTS: 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. CONCLUSIONS: 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.