Recruiting the host's immune system to target Helicobacter pylori's surface glycans.

Due to the increased prevalence of bacterial strains that are resistant to existing antibiotics, there is an urgent need for new antibacterial strategies. Bacterial glycans are an attractive target for new treatments, as they are frequently linked to pathogenesis and contain distinctive structures that are absent in humans. We set out to develop a novel targeting strategy based on surface glycans present on the gastric pathogen Helicobacter pylori (Hp). In this study, metabolic labeling of bacterial glycans with an azide-containing sugar allowed selective delivery of immune stimulants to azide-covered Hp. We established that Hp's surface glycans are labeled by treatment with the metabolic substrate peracetylated N-azidoacetylglucosamine (Ac4 GlcNAz). By contrast, mammalian cells treated with Ac4 GlcNAz exhibited no incorporation of the chemical label within extracellular glycans. We further demonstrated that the Staudinger ligation between azides and phosphines proceeds under acidic conditions with only a small loss of efficiency. We then targeted azide-covered Hp with phosphines conjugated to the immune stimulant 2,4-dinitrophenyl (DNP), a compound capable of directing a host immune response against these cells. Finally, we report that immune effector cells catalyze selective damage in vitro to DNP-covered Hp in the presence of anti-DNP antibodies. The technology reported herein represents a novel strategy to target Hp based on its glycans.

C-terminal methylation of truncated neuropeptides: an enzyme-assisted extraction artifact involving methanol.

Neuropeptides are the largest class of signaling molecules used by nervous systems. Today, neuropeptide discovery commonly involves chemical extraction from a tissue source followed by mass spectrometric characterization. Ideally, the extraction procedure accurately preserves the sequence and any inherent modifications of the native peptides. Here, we present data showing that this is not always true. Specifically, we present evidence showing that, in the lobster Homarus americanus, the orcokinin family members, NFDEIDRSGFG-OMe and SSEDMDRLGFG-OMe, are non-native peptides generated from full-length orcokinin precursors as the result of a highly selective peptide modification (peptide truncation with C-terminal methylation) that occurs during extraction. These peptides were observed by MALDI-FTMS and LC-Q-TOFMS analyses when eyestalk ganglia were extracted in a methanolic solvent, but not when tissues were dissected, co-crystallized with matrix, and analyzed directly with methanol excluded from the sample preparation. The identity of NFDEIDRSGFG-OMe was established using MALDI-FTMS/SORI-CID, LC-Q-TOFMS/MS, and comparison with a peptide standard. Extraction substituting deuterated methanol for methanol confirmed that the latter is the source of the C-terminal methyl group, and MS/MS confirmed the C-terminal localization of the added CD3. Surprisingly, NFDEIDRSGFG-OMe is not produced via a chemical acid-catalyzed esterification. Instead, the methylated peptide appears to result from proteolytic truncation in the presence of methanol, as evidenced by a reduction in conversion with the addition of a protease-inhibitor cocktail; heat effectively eliminated the conversion. This unusual and highly specific extraction-derived peptide conversion exemplifies the need to consider both chemical and biochemical processes that may modify the structure of endogenous neuropeptides.