Trypanosoma cruzi 13C-labeled O-Glycan standards for mass spectrometry

A solid-state nanopore-based single-molecule approach for label-free characterization of plant polysaccharides

Polysaccharides are important biomacromolecules existing in all plants, most of which are integrated into a fibrillar structure called the cell wall. In the absence of an effective methodology for polysaccharide analysis that arises from compositional heterogeneity and structural flexibility, our knowledge of cell wall architecture and function is greatly constrained. Here, we develop a single-molecule approach for identifying plant polysaccharides with acetylated modification levels. We designed a solid-state nanopore sensor supported by a free-standing SiN x membrane in fluidic cells. This device was able to detect cell wall polysaccharide xylans at concentrations as low as 5 ng/μL and discriminate xylans with hyperacetylated and unacetylated modifications. We further demonstrated the capability of this method in distinguishing arabinoxylan and glucuronoxylan in monocot and dicot plants. Combining the data for categorizing polysaccharide mixtures, our study establishes a single-molecule platform for polysaccharide analysis, opening a new avenue for understanding cell wall structures, and expanding polysaccharide applications.

Separation and Identification of Permethylated Glycan Isomers by Reversed Phase NanoLC-NSI-MSn

HPLC has been employed for decades to enhance detection sensitivity and quantification of complex analytes within biological mixtures. Among these analytes, glycans released from glycoproteins and glycolipids have been characterized as underivatized or fluorescently tagged derivatives by HPLC coupled to various detection methods. These approaches have proven extremely useful for profiling the structural diversity of glycoprotein and glycolipid glycosylation but require the availability of glycan standards and secondary orthogonal degradation strategies to validate structural assignments. A robust method for HPLC separation of glycans as their permethylated derivatives, coupled with in-line multidimensional ion fragmentation (MSn) to assign structural features independent of standards, would significantly enhance the depth of knowledge obtainable from biological samples. Here, we report an optimized workflow for LC-MS analysis of permethylated glycans that includes sample preparation, mobile phase optimization, and MSn method development to resolve structural isomers on-the-fly. We report baseline separation and MSn of isomeric N- and O-glycan structures, aided by supplementing mobile phases with Li+, which simplifies adduct heterogeneity and facilitates cross-ring fragmentation to obtain valuable monosaccharide linkage information. Our workflow has been adapted from standard proteomics-based workflows and, therefore, provides opportunities for laboratories with expertise in proteomics to acquire glycomic data with minimal deviation from existing buffer systems, chromatography media, and instrument configurations. Furthermore, our workflow does not require a mass spectrometer with high-resolution/accurate mass capabilities. The rapidly evolving appreciation of the biological significance of glycans for human health and disease requires the implementation of high-throughput methods to identify and quantify glycans harvested from sample sets of sufficient size to achieve appropriately powered statistical significance. The LC-MSn approach we report generates glycan isomeric separations and robust structural characterization and is amenable to autosampling with associated throughput enhancements.

Glycomics, Glycoproteomics, and Glycogenomics: An Inter-Taxa Evolutionary Perspective

Glycosylation is a highly diverse set of co- and posttranslational modifications of proteins. For mammalian glycoproteins, glycosylation is often site-, tissue-, and species-specific and diversified by microheterogeneity. Multitudinous biochemical, cellular, physiological, and organismic effects of their glycans have been revealed, either intrinsic to the carrier proteins or mediated by endogenous reader proteins with carbohydrate recognition domains. Furthermore, glycans frequently form the first line of access by or defense from foreign invaders, and new roles for nucleocytoplasmic glycosylation are blossoming. We now know enough to conclude that the same general principles apply in invertebrate animals and unicellular eukaryotes-different branches of which spawned the plants or fungi and animals. The two major driving forces for exploring the glycomes of invertebrates and protists are (i) to understand the biochemical basis of glycan-driven biology in these organisms, especially of pathogens, and (ii) to uncover the evolutionary relationships between glycans, their biosynthetic enzyme genes, and biological functions for new glycobiological insights. With an emphasis on emerging areas of protist glycobiology, here we offer an overview of glycan diversity and evolution, to promote future access to this treasure trove of glycobiological processes.

Synthesis of the hexasaccharide from Trypanosoma cruzi mucins with the Galp(1 → 2)Galf unit constructed with a superarmed thiogalactopyranosyl donor

Hexasaccharide β-D-Galp-(1→ 2)-[β-D-Galp-(1 → 3)]-β-D-Galp-(1 → 6)-[β-D-Galp-(1 → 2)-β-D-Galf-(1 → 4)]-D-GlcNAc (1) was found O-linked in mucins of Trypanosoma cruzi epimastigotes and metacyclic trypomatigotes. Studies on the biological pathways and functionalities of the mucin oligosaccharides are prompted in order to understand the interactions of these molecules with the insect host. Trisaccharide constituent β-D-Galp-(1 → 2)-β-D-Galf-(1 → 4)-D-GlcNAc was constructed from the reducing to the non-reducing end. We discuss the difficulties to introduce a Galp unit at the O-2 position of a partially protected galactofuranosyl unit which were overcome using an anchimerically superarmed donor. By this route and employing a [3 + 3] nitrilium convergent approach hexasaccharide 1 was synthesized in moderate yield.