Investigation of glycan evolution based on a comprehensive analysis of glycosyltransferases using phylogenetic profiling

Concerted Regulation of Glycosylation Factors Sustains Tissue Identity and Function

Glycosylation is a fundamental cellular process affecting human development and health. Complex machinery establishes the glycan structures whose heterogeneity provides greater structural diversity than other post-translational modifications. Although known to present spatial and temporal diversity, the evolution of glycosylation and its role at the tissue-specific level is poorly understood. In this study, we combined genome and transcriptome profiles of healthy and diseased tissues to uncover novel insights into the complex role of glycosylation in humans. We constructed a catalogue of human glycosylation factors, including transferases, hydrolases and other genes directly involved in glycosylation. These were categorized as involved in N-, O- and lipid-linked glycosylation, glypiation, and glycosaminoglycan synthesis. Our data showed that these glycosylation factors constitute an ancient family of genes, where evolutionary constraints suppressed large gene duplications, except for genes involved in O-linked and lipid glycosylation. The transcriptome profiles of 30 healthy human tissues revealed tissue-specific expression patterns preserved across mammals. In addition, clusters of tightly co-expressed genes suggest a glycosylation code underlying tissue identity. Interestingly, several glycosylation factors showed tissue-specific profiles varying with age, suggesting a role in ageing-related disorders. In cancer, our analysis revealed that glycosylation factors are highly perturbed, at the genome and transcriptome levels, with a strong predominance of copy number alterations. Moreover, glycosylation factor dysregulation was associated with distinct cellular compositions of the tumor microenvironment, reinforcing the impact of glycosylation in modulating the immune system. Overall, this work provides genome-wide evidence that the glycosylation machinery is tightly regulated in healthy tissues and impaired in ageing and tumorigenesis, unveiling novel potential roles as prognostic biomarkers or therapeutic targets.

Bombyx mori β1,4-N-acetylgalactosaminyltransferase possesses relaxed donor substrate specificity in N-glycan synthesis

N-Glycosylation is one of the most important post-translational protein modifications in eukaryotic cells. Although more than 200 N-glycogenes contributing to N-glycan biosynthesis have been identified and characterized, the information on insect N-glycosylation is still limited. Here, focusing on insect N-glycosylation, we characterized Bombyx mori N-acetylgalactosaminyltransferase (BmGalNAcT) participating in complex N-glycan biosynthesis in mammals. BmGalNAcT localized at the Golgi and was ubiquitously expressed in every organ and in the developmental stage of the middle silk gland of fifth instar larvae. Analysis of recombinant BmGalNAcT expressed in Sf9 cells showed that BmGalNAcT transferred GalNAc to non-reducing terminals of GlcNAcβ1,2-R with β1,4-linkage. In addition, BmGalNAcT mediated transfer of galactose and N-acetylglucosamine residues but not transfer of either glucose or glucuronic acid from the UDP-sugar donor substrate to the N-glycan. Despite this tri-functional sugar transfer activity, however, most of the endogenous glycoproteins of insect cells were present without GalNAc, Gal, or GlcNAc residues at the non-reducing terminal of β1,2-GlcNAc residue(s). Moreover, overexpression of BmGalNAcT in insect cells had no effect on N-acetylgalactosaminylation, galactosylation, or N-acetylglucosaminylation of the major N-glycan during biosynthesis. These results suggested that B. mori has a novel multifunctional glycosyltransferase, but the N-glycosylation is highly and strictly regulated by the endogenous N-glycosylation machineries.

Genome-Wide Analysis of Whole Human Glycoside Hydrolases by Data-Driven Analysis in Silico

Glycans are involved in various metabolic processes via the functions of glycosyltransferases and glycoside hydrolases. Analysing the evolution of these enzymes is essential for improving the understanding of glycan metabolism and function. Based on our previous study of glycosyltransferases, we performed a genome-wide analysis of whole human glycoside hydrolases using the UniProt, BRENDA, CAZy and KEGG databases. Using cluster analysis, 319 human glycoside hydrolases were classified into four clusters based on their similarity to enzymes conserved in chordates or metazoans (Class 1), metazoans (Class 2), metazoans and plants (Class 3) and eukaryotes (Class 4). The eukaryote and metazoan clusters included N- and O-glycoside hydrolases, respectively. The significant abundance of disordered regions within the most conserved cluster indicated a role for disordered regions in the evolution of glycoside hydrolases. These results suggest that the biological diversity of multicellular organisms is related to the acquisition of N- and O-linked glycans.

Identifying adhesive components in a model tunicate

Tunicates populate a great variety of marine underwater substrates worldwide and represent a significant concern in marine shipping and aquaculture. Adhesives are secreted from the anterior papillae of their swimming larvae, which attach and metamorphose into permanently adhering, filter-feeding adults. We recently described the cellular composition of the sensory adhesive organ of the model tunicate Ciona intestinalis in great detail. Notably, the adhesive secretions of collocytes accumulate at the tip of the organ and contain glycoproteins. Here, we further explore the components of adhesive secretions and have screened for additional specificities that may influence adhesion or cohesion of the Ciona glue, including other carbohydrate moieties, catechols and substrate properties. We found a distinct set of sugar residues in the glue recognized by specific lectins with little overlap to other known marine adhesives. Surprisingly, we also detect catechol residues that likely originate from an adjacent cellular reservoir, the test cells. Furthermore, we provide information on substrate preferences where hydrophobicity outperforms charge in the attachment. Finally, we can influence the settlement process by the addition of hydrophilic heparin. The further analysis of tunicate adhesive strategies should provide a valuable knowledge source in designing physiological adhesives or green antifoulants. This article is part of the theme issue 'Transdisciplinary approaches to the study of adhesion and adhesives in biological systems'.