N-glycosylation is a conserved enzymatic process in eukaryotes that begins in the endoplasmic reticulum, where a Glc3Man9GlcNAc2 precursor is transferred to a growing peptide chain, and continues in the Golgi apparatus, where mannose residues are trimmed and distinct terminal motifs are added. The resulting glycans influence protein folding, receptor-ligand binding and cell adhesion, and their alteration in humans underlies congenital disorders of glycosylation and lysosomal storage disease. Schistosomes display characteristic N-glycan motifs, including LacdiNAc, multi-fucosylated LacdiNAc and LacNAc, together with core β1-2xylose and α1-6fucose modifications that are absent from human glycans. Each schistosome species and life stage carries its own glycan signature, and as the larvae journey through the mammalian host, the profile changes dynamically: core xylose and fucosylated LacNAc decline while LacdiNAc rises, sex-specific glycans eventually distinguish adult females from males, and glycans on extracellular vesicles released by the parasite shift in parallel, mediating recognition by host C-type lectin receptors.

To probe whether this shifting sugar landscape matters for development, the team cultured newly transformed Schistosoma mansoni schistosomula in vitro for up to six weeks, mimicking the larval maturation that normally takes five to seven weeks inside the host. They remodelled the parasite N-glycome with two α-mannosidase inhibitors: kifunensine, which blocks α-mannosidase I and thereby prevents the removal of α1-2-linked mannose residues, and swainsonine, which inhibits Golgi α-mannosidase II as well as lysosomal and cytosolic α-mannosidases. A high-throughput imaging screen showed that neither compound had any overt toxicity: after 72 and 120 hours of exposure, the motility and phenotype scores of treated schistosomula clustered with negative controls, while parasites exposed to the known anti-schistosomal compounds auranofin and praziquantel scored aberrantly on both metrics.

The glycan analysis revealed how profoundly the inhibitors reshaped the parasite’s N-glycosylation. Newly transformed schistosomula carried a median of 84.9 percent complex N-glycans, but within the first week of culture the profile shifted markedly, with control parasites settling at roughly 60 percent complex and 30 percent oligomannose structures. Kifunensine treatment pushed oligomannose N-glycans to 72.2 percent at week one, dominated by structures with nine (M9) and eight (M8) mannose residues, and by week six oligomannose accounted for 93 percent of the profile. Swainsonine produced a different signature: oligomannose at 44.4 percent, hybrid N-glycans at 11.4 percent, and, strikingly, free N-glycans bearing only one core GlcNAc at 16.4 percent, an effect attributed to inhibition of cytosolic α-mannosidase. The inhibitors also suppressed the developmental motifs: in kifunensine-treated parasites, core xylose fell from 11.2 percent at week one to one percent or less from week three onwards, core fucose dropped from 24.1 percent to around three percent or less, the LacNAc motif dwindled and the rise of LacdiNAc was prevented entirely. Swainsonine had a milder effect on core modifications but clearly curtailed LacNAc and LacdiNAc, which sit mostly on complex glycans.

Western and lectin blotting confirmed that these mass spectrometric changes were reflected at the glycoprotein level. The lectin Concanavalin A, which binds strongly to high-mannose structures, detected additional glycoprotein bands in kifunensine-treated parasites at weeks three and six, while the monoclonal antibody 100-4G11, which recognises the trimannosyl core motif, revealed an intense band between 25 and 37 kilodaltons after swainsonine treatment. The team also corrected meticulously for human-derived N-glycans contaminating the parasite extracts, since the culture medium contains human serum and red blood cells, using sialylated marker structures to subtract the host contribution from each spectrum.

Perhaps the most consequential finding emerged from the microscopy. By week four, a subset of continuously kifunensine-treated schistosomula developed local oedema: the body became locally bloated and darkened by what appeared to be accumulated hemozoin in the gut. The phenotype affected 8.2 percent of parasites at week four, rising to 21.9 percent at week six, compared with only 3.4 percent in controls, and it appeared consistently across three biological replicates. Confocal imaging with live dyes for nuclei, actin and cell membranes confirmed the gut disorganisation and revealed similar, subtler alterations in swainsonine-treated parasites that brightfield microscopy had missed. Normal developmental landmarks, including oral and ventral suckers, oesophagus, muscle layer, tegument and the beginnings of sexual dimorphism, were nonetheless evident in all conditions by week six.

Crucially, the team also discontinued the inhibitor treatment after the first week. The N-glycan profiles of both kifunensine- and swainsonine-treated parasites then recovered, returning to a pattern similar to controls by week three, and no oedema or other visible abnormality appeared at week four or later. This temporal dissociation is telling: sustained glycan perturbation during the larval maturation period disturbed development, whereas a brief glycan shift confined to the first week did not. The authors suggest that the oedema could stem from altered N-glycosylation of cell adhesion proteins such as E-cadherin and integrins, whose adhesive functions are known to depend on their glycan type, or from disruption of the digestive function of the schistosome gut, whose glycoproteins carry highly complex N-glycans. Differentiation of mammalian intestinal epithelial cells is itself accompanied by a decrease in highly mannosylated structures and upregulation of Golgi α-mannosidases, hinting that mannose trimming is a signal for tissue organisation in the parasite as well.

The study builds on the team’s earlier work showing that the same inhibitors remodelled the N-glycans of adult schistosomes without apparent harm, and it now extends glycan remodelling to the larval stage, where development is most extensive and the glycan profile changes most dynamically. The in vitro maturation of the control parasites closely mirrored previously published in vivo glycan profiles, with LacdiNAc rising, core xylosylated structures disappearing and core-fucosylated glycans declining, validating the culture system as a model for intra-mammalian development.

Yet the rapid recovery of the glycan profile after treatment withdrawal also exposes a limitation: chemical α-mannosidase inhibition is not suited for long-term co-culture experiments or in vivo studies, because the parasite simply restores its normal glycans once the compound is gone. The authors therefore point toward more durable glycoengineering approaches, including RNA interference to knock down glycosylation enzymes in a species-specific manner, and CRISPR-Cas9 genome editing, which has already been applied to schistosomula, adult worms and eggs, to create parasites with permanently altered glycan profiles. Such tools would also allow selective manipulation of individual motifs or of other glycan classes, such as O-glycans and glycosphingolipids, which broad-spectrum inhibitors cannot achieve.

For a field urgently seeking prophylactic vaccines and drugs against a parasite that evades and modulates host immunity with remarkable sophistication, glyco-remodelled live schistosomes now provide an attractive experimental platform. By tuning the parasite’s sugar coat and watching development falter or recover, researchers can begin to assign functional roles to individual glycans in larval survival, immune recognition and host interaction, exposing tentative glycan-based targets for the next generation of schistosomiasis control strategies and, potentially, for other neglected tropical diseases at large.

Subject of Research: Chemical inhibition of α-mannosidase in S. mansoni schistosomula leads to reshaped N-glycosylation associated with developmental alterations

Article Title: Chemical inhibition of α-mannosidase in S. mansoni schistosomula leads to reshaped N-glycosylation associated with developmental alterations

Article References: Kuhlemaijer, E. B., Veldhuizen, T., Hoekstra, Q. C. A., Umbach, J. A., Niezen, M. J., Forde-Thomas, J. E., Rinaldi, G., Hoffmann, K. F., van Diepen, A., & Hokke, C. H. (2026). Chemical inhibition of α-mannosidase in S. mansoni schistosomula leads to reshaped N-glycosylation associated with developmental alterations. Frontiers in Parasitology, 5, Article 1930872. https://doi.org/10.3389/fpara.2026.1930872

Image Credits: AI Generated

DOI: 10.3389/fpara.2026.1930872

Keywords: Chemical, inhibition, mannosidase, mansoni, schistosomula, leads, reshaped, N-glycosylation, associated, developmental, alterations, scientific research

The spike protein is the multimeric engine of coronavirus entry. Its larger S1 subunit carries the receptor-binding machinery that latches onto ACE2 on the surface of human cells, while the smaller S2 subunit is the fusogenic core that, once triggered, refolds to drive merger of the viral envelope with the host cell membrane. Between these two subunits sits a polybasic cleavage motif, the RRAR sequence that distinguishes SARS-CoV-2 from many related coronaviruses and that is recognised and cut by furin and other proprotein convertases within the producing cell. This cleavage event, termed priming, is not decorative: it pre-activates the spike so that the virus is poised for rapid membrane fusion upon receptor engagement, a property widely credited with contributing to efficient human-to-human transmission.

What makes the region around the cleavage site chemically complex is that the spike is one of the most heavily glycosylated proteins known in virology, carrying 22 N-linked glycans per protomer. These carbohydrates serve the canonical functions of shielding immunodominant epitopes and escorting the protein through the folding and quality-control machinery of the endoplasmic reticulum and Golgi apparatus. But several of the glycosylation sequons sit remarkably close to the S1/S2 junction, raising a long-standing question: do these sugars physically modulate access of furin to the polybasic motif, and if so, does removing them cripple the entry functions of the spike?

To answer this, Muriel Lavie, Emma Louvet, Jules Patron, Xavier Hanoulle and Sandrine Belouzard systematically mutated the asparagine residues at positions 603, 616 and 657, individually and in combination, thereby ablating the corresponding N-glycans without otherwise altering the spike sequence. They then measured three tightly linked readouts in cell systems: the efficiency with which the spike was cleaved into its S1 and S2 subunits, the capacity of the processed spike to mediate cell–cell fusion, and its ability to support entry of pseudotyped particles into target cells expressing ACE2. The comparative dimension of the design is what gives the work its evolutionary punch, because the same mutant panel was assessed on two distinct genetic backgrounds: the D614 variant and its G614 descendant that rapidly became globally dominant in 2020, and the XBB.1.5 Omicron variant that circulated widely in 2023.

The first major finding concerns a compensatory basic residue. When the three glycans were removed simultaneously, cleavage of the spike did not simply collapse; instead, the authors found that processing of the glycan-deficient spike became dependent on arginine at position 634, a basic residue lying within the cleavage-proximal region. In other words, the loss of the sugar shield exposed a functional redundancy in the local sequence: with the glycans gone, the enzymatic machinery that processes the spike leans on the R634 residue to achieve productive cutting. This interplay between carbohydrate occupancy and a specific cationic side chain underscores how finely balanced the protease-recognition landscape around the S1/S2 junction really is, and it suggests that the local electrostatic and steric environment — not merely the canonical RRAR motif — determines whether priming occurs efficiently.

The second finding is that on the D614 and G614 backgrounds, the glycans at 603, 616 and 657 and the R634 residue are each required for full fusion and entry competence. Mutating these positions on those variants produced measurable deficits in both cell–cell fusion assays and pseudotype entry, indicating that the glycan cluster and the compensatory basic residue act in concert to maintain the entry functions that follow successful cleavage. The consistency across D614 and G614 is notable because the G614 substitution itself is known to stabilise the spike and increase its incorporation into virions; the new data indicate that even on that stabilised backbone, the cleavage-site glycans remain non-negotiable structural elements.

The picture changes, however, when the same experiments are repeated on XBB.1.5. In the Omicron background, mutations of the three glycosylation sites and of R634 had a milder impact on spike processing and entry functions than they did in the ancestral variants. The authors conclude from this pattern that the functional roles of N603, N616, N657 and R634 have evolved alongside the circulating variants. This is a subtle but important point for evolutionary virology: Omicron lineages accumulated dozens of changes across the spike, including extensive remodeling of the receptor-binding domain and adjustments near the S1/S2 region, and the new results show that these changes have partially uncoupled entry competence from the glycan-and-arginine dependency that governed earlier forms of the virus.

Mechanistically, the results fit a model in which the upstream glycans act as steric modulators of furin accessibility. Bulky N-linked carbohydrates projecting from the peptide backbone around residues 603 to 657 can either occlude or funnel the protease toward the polybasic motif, depending on their precise position and occupancy. Removing them appears to perturb the local conformation in a way that shifts the burden of recognition onto nearby basic residues such as R634. At the same time, the glycans’ contribution to fusion and entry in D614 and G614 suggests they do more than merely regulate cleavage access; they may help stabilise the metastable pre-fusion architecture that the S2 subunit must maintain until the moment of triggering. Their reduced importance in XBB.1.5 implies that other sequence features of the Omicron spike have taken over some of that stabilising or presenting role.

The work also carries implications that extend beyond SARS-CoV-2 itself. The dependence of proteolytic priming on glycan context echoes findings in other enveloped viruses, where carbohydrates adjacent to cleavage sites modulate activation of fusion proteins. For coronavirus surveillance, the message is that mutations at N-glycosylation sequons near the S1/S2 boundary should not be dismissed as neutral surface noise; depending on the genetic background in which they appear, they can reshape how efficiently the spike is primed and how readily the virus enters cells. Conversely, the variant-dependent behaviour means that any prediction of a glycan mutation’s effect must account for the rest of the spike sequence — a caution against interpreting such changes in isolation.

For therapeutic and vaccine design, the study adds a further layer of nuance. Glycan-shielded regions of the spike are notoriously difficult targets for antibody-based countermeasures, but understanding which sugars are functionally load-bearing, and how their roles shift between variants, can inform the design of stabilized immunogens and small molecules that target the cleavage-proximal region. The Lille team’s findings, supported by the region Hauts-de-France through the REACT’EU programme and conducted with the imaging facilities of the BioImaging Center Lille Nord-de-France, reinforce a theme that has run through coronavirus structural biology since the pandemic began: the spike is not a static target but a dynamically glycosylated, protease-regulated machine, and its evolution must be read through that lens. As SARS-CoV-2 continues to diversify, the sugar chains flanking its activation switch may yet prove to be among the quiet arbiters of which variants rise and which fade.

Subject of Research: Role of N-glycans near the SARS-CoV-2 spike furin cleavage site in spike processing and viral entry

Article Title: Glycans located upstream of the furin cleavage site in SARS-CoV-2 Spike protein influence its processing and functions

Article References: Lavie, M., Louvet, E., Patron, J., Hanoulle, X., & Belouzard, S. (2026). Glycans located upstream of the furin cleavage site in SARS-CoV-2 Spike protein influence its processing and functions. Scientific Reports. https://doi.org/10.1038/s41598-026-70382-z

Image Credits: AI Generated

DOI: 10.1038/s41598-026-70382-z

Keywords: SARS-CoV-2, spike glycoprotein, furin cleavage, N-glycosylation, S1/S2 processing, membrane fusion, viral entry, D614G, Omicron XBB.1.5, glycan shield, R634, Scientific Reports

A team led by Jian-Feng Li at Sun Yat-sen University in Guangzhou, working with collaborators at South China Agricultural University, the Chinese University of Hong Kong and the University of Macau, identified two paralogous chitinases in the model plant Arabidopsis thaliana that they named MIC1 and MIC2. Both genes are induced by chitin and by other microbe-associated molecular patterns, including the bacterial flagellin-derived peptide flg22 and the elongation factor Tu-derived peptide elf18. Both proteins are secreted into the apoplast, the fluid-filled space outside the plant cell membrane where fungal contact first occurs, and both possess direct antifungal activity in vitro, breaking down chitin in the fungal cell wall itself. On the surface, the two enzymes look like redundant copies of the same tool.

The resemblance is deceptive. When the researchers generated CRISPR/Cas9 knockout mutants, the two paralogs pulled in opposite directions. Plants lacking MIC1 became markedly more resistant to the grey mould pathogen Botrytis cinerea and to the vascular wilt fungus Verticillium dahliae, while plants lacking MIC2 became more susceptible. The team also showed that the single mutants and the mic1 mic2 double mutant grow normally under standard conditions, which means the antagonistic effects of these enzymes are specific to immune outcomes rather than general developmental defects. The picture that emerged is of two enzymes with the same substrate but opposing roles in tuning the immune response.

The key to this antagonism lies in the products of chitin digestion. Chitin is a polymer of N-acetylglucosamine units, conventionally abbreviated NAG, and the length of the oligomers released by hydrolysis determines their biological meaning. Using high-performance liquid chromatography to track the fate of defined chitin oligomers, the researchers found that MIC2 cleaves long chitin chains into intermediate fragments, principally NAG4 to NAG6, which are precisely the sizes that plant chitin receptors recognize as immunogenic elicitors. These fragments activate mitogen-activated protein kinase signalling, a canonical early readout of chitin-triggered immunity, and pretreatment with NAG4 primed Arabidopsis leaves for enhanced resistance against B. cinerea. MIC2, in other words, is an alarm bell: it chews the fungal wall in a way that generates the molecular signals that rally the plant’s defenses.

MIC1 does the opposite. Rather than stopping at immunogenic intermediates, MIC1 processes chitin all the way down to NAG2 dimers and NAG1 monomers, fragments that are too short to activate receptor signalling. In seedling assays, exogenous chitin normally inhibits root growth, a visible manifestation of constitutive chitin signalling, and MIC1 is the enzyme responsible for preventing this self-inflicted damage. When the researchers tested additional Arabidopsis chitinases from other clades, they found that the MIC1-like degradation pattern, exemplified by the clade IV enzyme chitIV1, is functionally conserved, and that deleting whole clusters of MIC1-like genes reproduced the chitin-hypersensitive growth phenotype. MIC1 and its relatives therefore act as a molecular off-switch, extinguishing the growth-inhibitory signal once the immune alarm has sounded.

What makes one enzyme stop at immunogenic fragments while its near-identical paralog grinds chitin to dust? The answer, uncovered through a combination of mass spectrometry, PNGase digestion assays and site-directed mutagenesis, is N-glycosylation, the attachment of sugar chains to asparagine residues of secreted proteins. Both MIC1 and MIC2 carry N-glycans, and these modifications are not decorative: glycosylation-deficient variants of either protein failed to be secreted efficiently into the apoplast, and a glycosylation-deficient MIC2 could no longer complement the enhanced susceptibility of mic1 mic2 double mutants to B. cinerea. Glycosylation is thus required for these enzymes to reach their site of action at all.

But one glycan does far more than ensure secretion. Mass spectrometry mapped three N-glycosylation sites on MIC1 and two on MIC2, and the decisive difference came down to a single residue: asparagine 137 in MIC1. When the researchers swapped variable segments between the two proteins to create chimeric enzymes, the exchange that transferred the MIC1 region containing Asn137 into MIC2 converted MIC2 into a MIC1-like enzyme, digesting NAG7 into more dimers and monomers and fewer immunogenic pentamers and tetramers. Conversely, the corresponding chimeric version of MIC1 lost its characteristic band shift and behaved more like MIC2. In complementation tests, the chimeric MIC2 carrying the MIC1 glycosylation region partially suppressed chitin-induced growth inhibition, whereas wild-type MIC2 did not, and it slightly increased susceptibility to B. cinerea instead of restoring resistance. Removing the Asn137 glycan from MIC1 converted it into a MIC2-like enzyme, demonstrating that this one sugar attachment dictates the chitinolytic specificity of the entire protein.

Structural modelling with AlphaFold showed that MIC1 and MIC2 are highly similar in sequence and fold, with their catalytic glutamates aligned and their glycosylation sites positioned on surface loops, including the Loop III region implicated in substrate handling in GH19 family chitinases. The Asn137 glycan apparently reshapes the local architecture of the catalytic cleft in a way that changes how many NAG units the enzyme removes per cleavage event. This is a remarkable example of post-translational modification acting as a functional diversification code: two genes born of duplication, nearly interchangeable in sequence, are sorted into opposing immune roles by a single covalently attached oligosaccharide. The authors describe this as an N-glycosylation code governing the functional specialization of paralogous chitinases.

The implications extend well beyond Arabidopsis. A bioinformatic survey revealed that MIC1-like chitinases are widespread across the plant kingdom, and the Asn137-equivalent residue is highly conserved among MIC1 orthologs from different Arabidopsis ecotypes. The team turned to rice, the world’s most important staple crop, and generated CRISPR knockout mutants of the rice ortholog OsMIC1. The osmic1 mutants showed enhanced resistance to rice blast and to bacterial blight, the latter an intriguing bonus suggesting the mechanism is not strictly antifungal, while their grain length, grain width and thousand-grain weight remained indistinguishable from wild-type plants. Like their Arabidopsis counterparts, however, osmic1 seedlings did exhibit chitin-induced root growth inhibition, confirming that the dampening function of OsMIC1 is conserved.

For breeders, this is the rare kind of result that points directly at a molecular target. Fungal pathogens destroy a substantial fraction of global crop yields each year, and conventional resistance breeding often trades yield for defense. The MIC1/MIC2 system suggests a third path: tune the enzymatic processing of a universal pathogen-derived signal so that immunity is amplified without the growth penalty that constitutive immune signalling imposes. Editing or selecting variants of MIC1-like chitinases, or manipulating the glycosylation machinery that controls them, could in principle produce crops that detect and respond to fungal attack more vigorously while growing as if no pathogen were present. A single sugar on a single asparagine, it turns out, may hold the balance between feast and famine in the plant kingdom.

Subject of Research: N-glycosylation-dependent functional divergence of paralogous plant chitinases balancing immunity and growth

Article Title: N-glycosylation code diversifies paralogous chitinases to balance plant immunity and growth

Article References: Li, C., Lin, X.-X., Tian, L., Sun, W., Liu, J., Liu, Q., Du, Y., Jiang, X., Liang, Z., Deng, Y. Z., Au, S. W. N., Wan, J.-B., & Li, J.-F. (2026). N-glycosylation code diversifies paralogous chitinases to balance plant immunity and growth. Nature Plants. https://doi.org/10.1038/s41477-026-02420-7

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02420-7

Keywords: chitinases, N-glycosylation, plant immunity, chitin signalling, Arabidopsis thaliana, MIC1, MIC2, growth-defense trade-off, fungal resistance, rice breeding, apoplast, CRISPR

The research, led by Xiaobin Wei, Mengyi Yao and Pingping Zhao of Henan University together with colleagues at the Shanghai Institute of Materia Medica and Guangzhou Medical University, focused on the signalling module formed by the SCREW/CTNIP peptide family, their receptor NUT/HSL3 and the co-receptor BAK1/SERK3. Earlier work had established that SCREW-type peptides, sometimes described as phytocytokines, promote the reopening of stomata that have closed in response to the stress hormone abscisic acid or to microbe-associated molecular patterns, thereby restoring photosynthesis and gas exchange while lowering apoplast water saturation to inhibit pathogen proliferation. What remained unknown was precisely how the receptor recognizes these peptides and assembles the active signalling complex on the cell surface.

To answer that question, the team turned to cryo-electron microscopy. They determined the structure of the extracellular domain of the Arabidopsis receptor AtNUT on its own and, more importantly, the structure of the ternary complex in which AtNUT binds the peptide SCREW2 and recruits the co-receptor AtBAK1. The resulting maps, deposited in the Electron Microscopy Data Bank under accession codes EMD-65054 and EMD-65053, with atomic coordinates in the Protein Data Bank as entries 9VH3 and 9VH2, provide the first three-dimensional portrait of this immune-modulating receptor assembly.

The most striking discovery concerns the shape of the peptide itself. Most plant peptides that bind leucine-rich repeat receptor kinases adopt one of two well-characterized conformations: an omega-like, hairpin-shaped fold seen in complexes such as HAESA–IDA–SERK1, HSL1–CLE9–SERK1 and PXY–CLE41–SERK2, or a fully extended configuration seen in the immune complexes MIK2–SCOOP12–BAK1 and FLS2–flg22–BAK1. SCREW2 does neither. Instead, it adopts what the authors call a cross-ribbon conformation, an inverted arrangement in which the peptide’s termini cross over in a way that has not been observed for any other LRR receptor-binding peptide. This distinctive fold is stabilized by intramolecular interactions, including conserved disulfide bonds and hydrogen-bonding networks that tie the N- and C-terminal regions together and lock the central loop into place.

The cross-ribbon architecture is not merely a structural curiosity; it is the molecular basis of specificity. Because the peptide presents its recognition surfaces in an arrangement unique to the SCREW family, only AtNUT possesses a binding surface complementary to it. The structure shows how conserved residues of SCREW2, including the completely conserved serine and asparagine residues near the N-terminus and the highly conserved CTNIP motif within the central loop, dock into a matching pocket on AtNUT. Once the peptide is seated in its receptor, its spatial configuration creates the platform needed to recruit AtBAK1, the promiscuous SERK-family co-receptor that participates in a wide range of plant receptor kinase signalling pathways, from brassinosteroid perception to innate immunity.

One of the most unexpected findings involves a sugar. The structure revealed an N-linked glycan attached to asparagine 449 of AtNUT, positioned directly within the peptide-binding interface. The glycan forms a hydrogen bond with the arginine 63 residue of SCREW2, effectively acting as a molecular handhold that helps grip the peptide. Biochemical assays using surface plasmon resonance confirmed that mutating the N449 glycosylation site significantly weakens SCREW2 binding. Sequence alignments across Brassicaceae species show that the N449 site and the surrounding N-X-S/T glycosylation motifs are conserved, suggesting that this sugar-assisted recognition mechanism is a general feature of NUT-family receptors rather than an idiosyncrasy of Arabidopsis.

The structural insights translated directly into functional predictions. When the researchers mutated the SCREW2 recognition sites on AtNUT, the consequences rippled through the entire downstream signalling cascade. Mitogen-activated protein kinase activation, a hallmark early response of pattern-triggered immunity, was significantly attenuated, as was the expression of PTI marker genes measured by RT-qPCR. These experiments demonstrate that the precise peptide-receptor contacts visualized in the cryo-EM maps are not incidental; they are load-bearing elements of the signalling pathway that counteracts abscisic acid- and MAMP-triggered stomatal closure.

The work also clarifies how the SCREW/NUT module fits into the broader logic of stomatal immunity. Pathogen attack triggers closure through well-mapped pathways involving abscisic acid receptors of the PYR/PYL/RCAR family, the SLAC1 anion channel and calcium-permeable channels such as OSCA1.3. Reopening, by contrast, requires actively counteracting these closure signals. The new structures suggest a model in which SCREW peptide binding induces heterodimerization of AtNUT and AtBAK1, initiating a transphosphorylation cascade that pushes guard cells back toward the open state. In this view, the plant does not simply reverse closure passively but deploys a dedicated peptide-receptor system whose activation is gated by the unique cross-ribbon geometry of its ligand.

From an applied perspective, the findings open concrete avenues for crop improvement. Stomatal dynamics sit at the heart of the trade-off between drought tolerance, photosynthetic productivity and disease resistance, and engineering this balance has long been hampered by incomplete knowledge of the underlying receptors. Because the SCREW recognition surface, the N449 glycan dependence and the co-receptor recruitment interface are now defined at the residue level, breeders and synthetic biologists have a structural template for tuning stomatal reopening without broadly disabling immune signalling. Sequence comparisons across angiosperms, from wheat and rice to grapevine and tomato, indicate that SCREW homologs and their conserved cysteine scaffolds are widespread, raising the prospect that the mechanism characterized here in Arabidopsis can be translated to staple crops.

The study also adds a new chapter to the structural biology of plant receptor kinases. For years, the field has recognized that leucine-rich repeat receptors rely on a common architectural principle: a peptide ligand bridges the receptor and a SERK co-receptor, with the peptide’s C-terminus typically engaging the co-receptor’s recruitment loop. The SCREW2 structure breaks that pattern, demonstrating that peptide geometry itself can be the determinant of receptor identity and that glycans can participate directly in ligand recognition rather than merely assisting protein folding and quality control. As cryo-EM continues to expose the extracellular signalling complexes of plant membranes, cases like SCREW/NUT are likely to multiply, revealing a molecular vocabulary far richer than the canonical models anticipated. For now, the cross-ribbon peptide stands as a vivid reminder that in biology, shape is often the message.

Subject of Research: Cryo-EM structural mechanism of SCREW/CTNIP peptide recognition by the NUT/HSL3–BAK1 receptor complex in plant stomatal immunity

Article Title: Cross-ribbon conformation defines peptide recognition in SCREW/CTNIP–NUT/HSL3 signalling

Article References: Wei, X., Yao, M., Zhao, P., Zhang, X., Zhang, K., Hu, W., Shi, J., Guo, S., Li, R., Wang, W., Xu, Y., Guo, S., Xu, H. E., & Song, C.-P. (2026). Cross-ribbon conformation defines peptide recognition in SCREW/CTNIP–NUT/HSL3 signalling. Nature Plants, 12(9), 1769-1781. https://doi.org/10.1038/s41477-026-02376-8

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02376-8

Keywords: SCREW/CTNIP peptides, NUT/HSL3 receptor, BAK1/SERK3 co-receptor, cryo-EM structure, cross-ribbon conformation, stomatal immunity, N-glycosylation, pattern-triggered immunity, plant receptor kinases, stomatal reopening, Arabidopsis, Nature Plants

The team’s central question was deceptively simple: does the N-glycosylation of extracellular matrix proteins, the enzymatic attachment of complex glycans to asparagine residues, provide information about cancer-associated fibroblast biology that goes beyond simply knowing how much of each protein is present? To answer it, the investigators turned to one of the richest public resources in cancer proteomics, the Clinical Proteomic Tumor Analysis Consortium pancreatic cancer dataset. They integrated peptide-level and site-level N-glycoproteomics from 135 pancreatic ductal adenocarcinoma tumors with matched proteomics, RNA expression data, clinical covariates, external transcriptomic cohorts, and spatial transcriptomics. Five adenosquamous tumors were retained only for sensitivity analyses, ensuring that the main findings reflected the conventional ductal histology.

The methodological heart of the study lies in a statistical maneuver called protein-residualization. For each ECM glycopeptide and glycosylation site, the researchers regressed out the abundance of the matched parent protein, leaving behind what they term protein-residual ECM N-glycosylation scores. In plain terms, they asked whether a given ECM protein is more or less heavily glycosylated than its own abundance would predict, and whether that excess or deficit of glycosylation tells a coherent biological story. This is a post-translational readout: it captures enzymatic and cellular regulation of glycan assembly that cannot be inferred from gene expression or raw protein levels alone. The approach is conceptually analogous to looking not at how many bricks were delivered to a construction site, but at how those bricks were finished and treated, which may reveal which crew is doing the building.

What emerged was a striking and reproducible association. Residual ECM N-glycoprotein scores were significantly linked to the conventional myofibroblastic cancer-associated fibroblast phenotype, known as myCAF, with adjusted beta coefficients of 0.426 and 0.425, and to broader CAF and stromal phenotypes with betas of 0.304 and 0.312. Critically, these associations survived adjustment for the proteome matrisome score, stromal fraction, and neoplastic cellularity, meaning the glycosylation signal was not simply a disguised measure of having more stroma or fewer tumor cells. The signal was distributed across a candidate program of ECM glycoproteins rather than driven by a single molecule, which strengthens the interpretation that it reflects a coordinated stromal cell state rather than a technical artifact.

Robustness was tested with unusual thoroughness. The authors evaluated nonlinear residualization schemes, detection-probability weighting, feature coverage thresholds, mass spectrometry acquisition plex, and random feature resampling. The myCAF association remained stable under nonlinear residualization, detection-probability weighting, observation thresholds ranging from 40 to 110 tumors, and random splitting of the glycosylation features. In an era when many multi-omics associations dissolve under scrutiny, this level of stress-testing lends considerable weight to the central claim. The team also examined CAF subtypes, glycan composition, spatial localization, and clinical context, building a multi-angled case that the glycosylation signature is a genuine biological phenomenon.

Among the composition-resolved findings, one stands out. When glycoforms were classified by glycan composition, high-mannose glycoforms on ECM proteins showed the strongest myCAF effects, with beta coefficients of 0.552 and 0.549. High-mannose N-glycans are relatively immature, unprocessed structures that can accumulate when glycan processing enzymes are altered or when proteins traffic through the secretory pathway differently. Their enrichment in the myCAF-associated stromal state suggests that myofibroblastic fibroblasts in pancreatic tumors may impose a distinctive glycan-processing environment on the matrix they deposit, and it nominates these glycoforms as concrete, testable translational candidates.

Spatial evidence provided independent confirmation. Using GeoMx digital spatial profiling, the researchers compared CAF-rich segments against epithelial segments in 20 patients and found that the candidate RNA program corresponding to the glycosylation signature was higher in the CAF segments in every single patient, with a mean paired difference of 1.234, a 95 percent bootstrap confidence interval of 1.054 to 1.389, and a p value of 9.57 times 10 to the minus 5. The corresponding candidate genes also localized to CAF-rich spatial niches in spatial transcriptomic data, and the pattern held across external transcriptomic cohorts, including resources from The Cancer Genome Atlas and the Gene Expression Omnibus. Convergence of proteomic, transcriptomic, and spatial lines of evidence on the same fibroblast state is exactly the kind of triangulation that translational scientists look for before investing in experimental validation.

The biological logic of the finding is worth unpacking. Cancer-associated fibroblasts in pancreatic cancer exist in several recognized states, including inflammatory iCAFs, antigen-presenting apCAFs, and contractile, matrix-producing myCAFs. MyCAFs are closely apposed to invasive tumor cells, deposit dense collagenous matrix, and have been linked in many studies to tumor progression, immune exclusion, and treatment resistance. If the glycosylation state of the ECM they build is a faithful readout of their activity, then measuring ECM glycopeptides offers a way to fingerprint the myCAF compartment in bulk tumor samples, something that single-cell and spatial methods capture but that has been difficult to access in standard proteomic workflows. In effect, the tumor’s sugar-coated scaffolding becomes a recording device for which fibroblast program dominated its construction.

The translational implications are twofold. First, protein-residual ECM N-glycosylation scores could serve as biomarkers that stratify pancreatic cancer patients by stromal biology, potentially identifying tumors dominated by myCAF activity without requiring spatial assays on every specimen. Second, the specific nomination of high-mannose ECM glycoforms and recurrent ECM glycoproteins gives glycosite-resolved experimental validation a concrete starting point. The authors are careful to frame these as candidates for validation rather than validated targets, and the study’s design, being based on public consortium data, means that functional experiments in model systems will be the necessary next step. Still, the fact that the signal survived such extensive robustness analyses and replicated across independent data modalities makes it a credible foundation for that work.

More broadly, the study contributes to a growing recognition that glycosylation is not biochemical decoration but a functional dimension of the tumor microenvironment. Glycans influence protein folding, stability, interactions with lectins, and immune recognition, and the ECM is a glycan-rich landscape that tumors remodel extensively. By showing that a post-translational, composition-resolved layer of the matrix encodes fibroblast state information invisible to protein abundance measurements, the researchers open a path toward glycoproteomics-informed stromal profiling in other fibrotic and desmoplastic tumors as well. For a disease like pancreatic cancer, where the stroma has long been both an obstacle and an enigma, the demonstration that its sugar signatures can be read, quantified, and mapped to a specific cellular state is a small but potentially consequential step toward therapies that target the ground the tumor stands on rather than the tumor alone.

Subject of Research: Protein-residual ECM N-glycosylation as a readout of myCAF-enriched stromal states in pancreatic ductal adenocarcinoma

Article Title: Protein-residual ECM N-glycosylation delineates a composition-resolved myCAF-enriched stromal state in pancreatic ductal adenocarcinoma

Article References: Feng, Y., Li, Z., Wang, H., Peng, Z., Tang, Y., Wei, Q., & Liu, H. (2026). Protein-residual ECM N-glycosylation delineates a composition-resolved myCAF-enriched stromal state in pancreatic ductal adenocarcinoma. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08974-6

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08974-6

Keywords: pancreatic ductal adenocarcinoma, N-glycosylation, glycoproteomics, extracellular matrix, cancer-associated fibroblasts, myCAF, high-mannose glycoforms, spatial transcriptomics, CPTAC, tumor microenvironment, biomarkers, Journal of Translational Medicine