Background: Trefoil factor 2 (TFF2) forms complexes with MUC6 and is concertedly secreted by deep gastric glands. Results: TFF2 is a lectin that binds to ␣-GlcNAc-capped MUC6 O-glycans with antibiotic activity against Helicobacter pylori. Conclusion: There may be a functional link between mucin glycans and TFF2 in H. pylori defense. Significance: The findings impact in development of defense strategies against H. pylori and in TFF2 receptor-mediated cell signaling.

The post-translational modification of proteins with O-GlcNAc is involved in various cellular processes including signal transduction, transcription, translation, and nuclear transport. This transient protein modification enables cells or tissues to adapt to nutrient conditions or stress. O-Glycosylation of the 26 S proteasome ATPase subunit Rpt2 is known to influence the stability of proteins by reducing their proteasome-dependent degradation. In contrast, knowledge of the sites of O-GlcNAcylation on the subunits of the catalytic core of the 26 S proteasome, the 20 S proteasome, and the impact on proteasome activity is very limited. This is predominantly because O-GlcNAc modifications are often substoichiometric and because 20 S proteasomes represent a complex protein mixture of different subtypes. Therefore, identification of O-GlcNAcylation sites on proteasome subunits essentially requires effective enrichment strategies. Here we describe an adapted β-elimination-based derivatization method of O-GlcNAc peptides using a novel biotin-cystamine tag. The specificity of the reaction was increased by differential isotopic labeling with either “light” biotin-cystamine or deuterated “heavy” biotin-cystamine. The enriched peptides were analyzed by LC-MALDI-TOF/TOF-MS and relatively quantified. The method was optimized using bovine α-crystallin and then applied to murine 20 S proteasomes isolated from spleen and brain and murine Hsp90 isolated from liver. Using this approach, we identified five novel and one known O-GlcNAc sites within the murine 20 S proteasome core complex that are located on five different subunits and in addition two novel O-GlcNAc sites on murine Hsp90β, of which one corresponds to a previously described phosphorylation site.

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Background: Absent microheterogeneity of LacdiNAc N-glycan on human gastric TFF2 points to high stringency control mechanism. Results: Single intact TFF domains of TFF2 control the ␤4-GalNAc transfer to terminal GlcNAc residues as conformational determinants. Conclusion:The role of a hydrophobic patch is hypothesized to form the essential part of the determinant. Significance: The restricted expression of LacdiNAc on extracellular matrix proteins relates to important biological processes.