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Extracellular Vesicle Glycosylation, Glycans and the Glycocalyx

Revisado por el equipo editorial de ExaVeyra Sciences · Actualizado el 20 de octubre de 2026

Extracellular vesicle glycosylation is the set of sugar chains that coat every vesicle: N-glycans and O-glycans on membrane proteins, glycosphingolipids in the outer leaflet, and heparan sulfate on proteoglycans.¹ These exosome glycans form a dense glycocalyx, the outermost layer of the vesicle.²

This page describes how the vesicle glycome is built, how laboratories measure it, how lectins read its terminal sugars, and how changing it alters where vesicles go. Each finding is attributed to the study that reported it.

Extracellular vesicle glycosylation spans proteins, lipids and proteoglycans

Glycosylation is the most abundant and structurally diverse modification of proteins in eukaryotic cells, built by a large network of glycosylation enzymes.³ Gerlach and Griffin describe the vesicle glycome as the surface oligosaccharides and polysaccharides of vesicles together with the carbohydrate-binding proteins found on and inside them (Fig. 1).⁴

N-linked glycans attach to asparagine

N-glycans are built on asparagine from a shared core and are processed into high-mannose, hybrid and complex forms.³ Saraswat and colleagues mapped this layer in human urinary exosomes and identified 126 N-glycopeptides from 51 glycosylation sites on 37 glycoproteins.⁵

O-linked glycans extend from serine and threonine

Mucin-type O-glycans begin with N-acetylgalactosamine on serine or threonine and are often short chains capped by galactose and sialic acid.³ Desantis and colleagues found vesicles from equine amniotic mesenchymal cells enriched in O-glycans ending in Galβ1,3GalNAc compared with their parent cells.⁶

Glycosphingolipids carry glycans in the outer leaflet

Glycosphingolipids join a glycan headgroup to ceramide, and on vesicles their sugars face outward.¹ Lo and colleagues profiled vesicles from human embryonic stem cells and found globo-series glycosphingolipids, including SSEA3 and SSEA4 ceramides, which the vesicles transferred into monocytes and macrophages.⁷

Macrophages primed with these vesicles, or with synthetic globo-series glycosphingolipids, took on features of decidual macrophages.⁷ Decidual macrophages in first-trimester tissue also expressed globo-series glycosphingolipids, placing this vesicle glycan class in the biology of embryo implantation.⁷

Syndecans display heparan sulfate

Syndecans are heparan sulfate proteoglycans. Baietti and colleagues showed that syndecans and their cytoplasmic adaptor syntenin, bound directly to ALIX, support the inward budding of endosomal membranes that forms exosomes.⁸ These syntenin exosomes depended on heparan sulfate, syndecans, ALIX and ESCRTs, and influenced the trafficking of FGF signals.⁸

Roucourt and colleagues then found that heparanase, which trims the heparan sulfate chains on syndecans, stimulates this pathway. It raised the exosomal secretion of syntenin, syndecan and CD63 and promoted their budding into endosomes.⁹

Extracellular vesicles carry a conserved glycan signature

Batista and colleagues compared vesicles from several biological sources with their parent cell membranes using lectin microarrays.¹⁰ Vesicles were enriched in high-mannose glycans, polylactosamine, α2,6-linked sialic acid and complex N-glycans, and they excluded the terminal blood group A and B antigens.¹⁰

The authors read this pattern as evidence that vesicles emerge from a specific membrane microdomain, with glycosylation contributing to protein sorting.¹⁰ Liang and colleagues then showed that complex N-glycans direct glycoproteins into vesicles, and that changing the N-glycan sites of EWI-2 altered how much of it was recruited.¹¹

Desantis and colleagues found equine amniotic cell vesicles enriched in α2,3-linked sialoglycans and high-mannose N-glycans,⁶ and Shimoda and colleagues found that vesicles from human adipose mesenchymal stem cells bound sialic acid-binding lectins more strongly than their parent membranes did.¹²

Saraswat and colleagues noted that a conserved glycan signature had been reported for exosomes from urine, T cell lines and human milk.⁵ Their glycoproteomic map of urinary exosomes, described below, identified glycoproteins and sites that carry it.⁵

Sialic acid and other terminal motifs cap the glycan coat

N-acetylneuraminic acid (Neu5Ac) is a nine-carbon sugar acid with the formula C11H19NO9, carrying a carboxylic acid and an acetamido group on its ring (Fig. 2).¹³ It sits at the outer ends of N-glycans, O-glycans and gangliosides, so it is often the first sugar a binding protein meets.¹

The carboxylic acid gives sialic acid a negative charge at physiological pH. Williams and colleagues measured a change in vesicle surface charge after neuraminidase removed terminal sialic acid, linking this sugar directly to the electrostatic character of the vesicle.¹⁴

The linkage of sialic acid to the sugar beneath it shapes recognition. Batista and colleagues found α2,6-linked sialic acid enriched on vesicles,¹⁰ and Saunderson and colleagues traced vesicle capture by the macrophage lectin CD169 to α2,3-linked sialic acid.¹⁵

Kundu and colleagues used a sialyltransferase to add azide-tagged sialic acids to exosomal glycans. The azide tags served as handles for attaching biotin, proteins or fluorophores by click chemistry.¹⁶ Labeling exosomes from different sources in this way revealed diverse glycosylation patterns between them.¹⁶

Lectin arrays, mass spectrometry and glycosidases measure exosome glycans

Gerlach and Griffin note that the small size of vesicles and the low yield from physiological samples make the glycome technically demanding to read.⁴ Williams and colleagues reviewed the glycomics methods applied to vesicles, which fall into three groups.¹

• Lectin arrays: binding profiles of intact vesicles, reporting their terminal glycan motifs.¹⁰
• Mass spectrometry: compositions, structures and attachment sites of released glycans and glycopeptides.⁵
• Glycosidase treatment: removal of N-glycans or sialic acid to test what each contributes to binding and uptake.¹⁴

Lectin arrays profile intact vesicles

Echevarria and colleagues screened lectin arrays and found three lectins that bound urinary vesicles with little or residual binding to urine matrix proteins. They built a bead-based method for lectin-based isolation of vesicles from urine on that result.¹⁷

Desantis and colleagues spotted cells and their vesicles directly onto microarray slides and probed them with a panel of 14 biotinylated lectins. Every lectin bound both samples, indicating that N-linked and O-linked glycans were present on the vesicles and the cells.⁶

Shimoda and colleagues used an evanescent-field lectin array to follow mesenchymal stem cell vesicles through osteogenic differentiation. Vesicles from differentiated cells bound fucose- and mannose-binding lectins more strongly, while their size, shape and marker proteins changed little.¹⁸

A later study from the same group compared vesicles by cell type, size and isolation method on a lectin microarray. Lectin-binding patterns depended on vesicle size and isolation method, which suggests that surface glycans can index vesicle heterogeneity.¹⁹

Mass spectrometry resolves structures and sites

Saraswat and colleagues combined tandem mass spectrometry of enriched glycopeptides with MALDI analysis of released glycans from urinary exosomes. They proposed structures for 87 N-glycopeptides and identified 66 unmodified N-glycan compositions, plus 13 sulfated or phosphorylated glycans.⁵

Glycosidases test what each glycan does

Glycosidases remove defined parts of the coat so their role can be tested. Williams and colleagues treated vesicles from two mouse liver cell lines with PNGase F, which releases N-glycans, and with neuraminidase, which cleaves terminal sialic acids.¹⁴

Terminal sugars determine which lectin binds a vesicle

Each lectin family reads a different terminal motif (Fig. 3). Galectins share carbohydrate recognition domains with affinity for small β-galactosides, and Seetharaman and colleagues solved the human galectin-3 domain bound to lactose and N-acetyllactosamine at 2.1 Å resolution (Fig. 4).²⁰

Galectin-3 pairs that single domain with an N-terminal domain through which it self-associates, which lets it bind multivalent glycan ligands.²¹ Barrès and colleagues found galectin-5 bound to the surface of rat reticulocyte exosomes, and adding galectin-5 reduced vesicle uptake by macrophages.²²

In the same study, the polylactosamine-rich glycoprotein Lamp2 left maturing reticulocytes on exosomes, consistent with galectin-5 sorting galactose-bearing glycoconjugates into vesicles.²² Polylactosamine is also one of the glycan motifs Batista and colleagues found enriched on vesicles.¹⁰

The dendritic cell receptor DC-SIGN binds high-mannose oligosaccharides and fucosylated blood group antigens, and it mediates endocytosis, releasing its ligand at endosomal pH.²³ Kuipers and colleagues found that DC-SIGN mediated most uptake of Schistosoma mansoni vesicles by human dendritic cells, whose surface N-glycans carried Lewis X.²⁴

Siglecs are sialic acid-binding immunoglobulin-like lectins. May and colleagues solved the N-terminal domain of sialoadhesin, also called Siglec-1 or CD169, bound to 3’-sialyllactose, and identified three residues conserved across the family as the core of the sialic acid-binding site (Fig. 5).²⁵

Siglec-1 is expressed by a subpopulation of macrophages and binds glycoconjugate ligands in a sialic acid-dependent manner.²⁶ Saunderson and colleagues showed that CD169 macrophages in the spleen marginal zone and lymph node subcapsular sinus capture B cell exosomes through their α2,3-linked sialic acids.¹⁵

In CD169-deficient mice, exosomes passed deeper into the lymph node paracortex and reached other splenic macrophages.¹⁵ Shimoda and colleagues likewise reported that Siglecs took part in the uptake of mesenchymal stem cell exosomes, which reached lymph nodes after injection under the skin of mice.¹²

Removing glycans changes vesicle uptake and biodistribution

Williams and colleagues found by flow cytometry that cells took up vesicles treated with PNGase F or neuraminidase with higher affinity than untreated vesicles.¹⁴ High-content screening showed that different cell types preferred different glycosylation states.¹⁴

The authors concluded that glycans tune uptake through charge, through direct glycan recognition, or both.¹⁴ Shimoda and colleagues glycoengineered vesicles with four distinct surface glycan patterns and found that cellular uptake and in vivo biodistribution both depended on the glycan profile.¹⁹

Royo and colleagues followed radiolabeled vesicles from mouse liver cells by positron emission tomography. Intravenous vesicles gathered quickly in the liver, and after neuraminidase removed terminal sialic acid, more of them accumulated in the lungs.²⁷

When the same vesicles were injected into the hock, the neuraminidase-treated ones distributed better to the axillary lymph nodes.²⁷ Kundu and colleagues, using sialic acid-tagged exosomes, identified macropinocytosis as the main uptake route, with other endocytic pathways contributing for specific exosomes.¹⁶

Tetraspanin and integrin glycosylation sits within the vesicle coat

The tetraspanin CD63 is a cell surface glycoprotein known to form complexes with integrins.²⁸ Its glycans and those of its integrin partners therefore sit inside the same coat that lectins read, alongside the glycolipids and proteoglycans of the vesicle membrane.¹

EWI-2 is a major partner of the tetraspanins CD9 and CD81.²⁹ Liang and colleagues showed that its recruitment into vesicles depends on its N-linked glycosylation sites, direct evidence that glycans help select which tetraspanin-associated proteins a vesicle carries.¹¹

Zheng and colleagues inserted a glycosylation domain into the large extracellular loop of CD63 and co-expressed fucosyltransferase VII or IX. The resulting vesicles displayed sialyl Lewis X or Lewis X and targeted activated endothelial cells or dendritic cells, respectively.²

Isogai and colleagues found that integrin β1 on small vesicles carried more highly branched complex N-glycans and more sialic acid than the same integrin in the parent cells.³⁰ Knocking out MGAT5, the enzyme that builds the branched N-glycans, or the sialyltransferase ST6GAL1 reduced vesicle binding to laminin.³⁰

The authors traced part of this effect to a single site. The N-glycan at asparagine 269, in the I-like domain of integrin β1, maintained the activated conformation of the integrin and enhanced laminin binding.³⁰

Some glycans define vesicle populations of their own. Tokoro and Kizuka found the neural glycan HNK-1 and its enzyme GlcAT-P in vesicles distinct from the tetraspanin-rich subtype, and these vesicles transferred HNK-1 to recipient cells.³¹

The exosome glycocalyx forms the outer interface of the vesicle

Wang and colleagues reviewed the vesicle surface as a composite of proteins, lipids and glycocalyx elements that governs targeting of recipient cells and selective cargo delivery.³² Its outermost glycan layer is the interface every receiving cell and soluble lectin meets first.²

Shurer and colleagues showed that mucin biopolymers and long polysaccharides generate entropic forces that favor curved membrane projections, and specific glycocalyx compositions drove the secretion of extracellular vesicles.³³ A polymer brush model predicted how polymer size and density shape these membrane forms.³³

Glycoengineering acts on this exposed layer. The display of sialyl Lewis X on CD63 and the enzymatic labeling of exosomal sialic acids both work by rewriting the glycocalyx directly.^2,16 Shimoda and colleagues proposed surface glycans as an index of vesicle heterogeneity, making this layer a descriptor of a preparation as well as a handle on it.¹⁹

Where to go from here

The uptake and cargo delivery reference follows vesicles after a lectin or receptor has bound them, and the lipidome reference covers the membrane that carries the glycolipids described here. The surface receptor chemistry and CD63 references describe the glycoproteins at the center of the coat.

The MISEV2023 quality reference explains how vesicle preparations are characterized. Verified practices can request lot-specific characterization data with the certificate of analysis, and our team is glad to discuss how a vesicle preparation was analyzed.