Biology subjects

Raba, G.

Publications and source records attributed to Raba, G..

3 recordsLinked to original sources

bioRxiv2026

Degradation of mucin O-glycans by a human gut symbiont requires a complex enzyme repertoire and promotes colonization

Secreted mucins are the major component of the mucus layer that protects intestinal epithelial surfaces by blocking excessive interactions with the microbiota. Mucins are complex glycoproteins decorated with over 100 different O-glycans. Some bacteria can utilize mucins and excessive degradation has been associated with disruption of the mucus barrier and inflammation. Despite the importance of mucins, a detailed enzymatic pathway by which gut bacteria degrade colonic mucin O-glycans and the impact of this process on gut colonization are unknown. Here, we identified >100 genes that are expressed by the symbiont Bacteroides thetaiotaomicron during growth on different O-glycan substrates, revealing effects of glycan structure on gene expression. The characterization of 33 glycoside hydrolase enzymes revealed the pathway for colonic O-glycan degradation by this bacterium. In vivo competition experiments show that multiple exo-acting enzymes targeting mucin capping structures are central to gut colonization and may provide targets to inhibit bacterial mucin degradation.

microbiology↗

bioRxiv2025

Cryo-EM structure of CLCA1 identifies CLCA1 as a founding member of a novel metzincin family.

Calcium-activated chloride channel regulator 1 (CLCA1) is implicated in several diseases, especially mucus-associated airway diseases, but its molecular function and regulation have remained unclear. By determining the structure of CLCA1 by negative stain electron microscopy and cryo-EM, we could confirm that CLCA1 forms large oligomeric complexes which adopts a compact domain organization comprising a metallohydrolase (MH), von Willebrand type A (VWA), {beta}-sheet-rich (BSR), inhibitory (ID), and fibronectin type III-like (FnIII-l) domains. The unusually large MH domain bears hallmarks of metzincins but is distinguished by several unique features including an atypical active site zinc-coordination environment and a second Zn2+ -coordination site. Unlike classical metzincins, CLCA1 lacks a pro-domain; instead, a C-terminal inhibitory loop occludes the MH active site, providing an alternative mechanism of autoinhibition. The adjacent VWA domain, resolved in its closed state, is poised for conformational change upon ligand binding, suggesting a route for allosteric regulation of protease activity. Structural and functional assays support a role for CLCA1 in cleaving glycosylated substrates, leading to alterations in mucin architecture consistent with a regulated function in mucus remodeling. Together, these data establish CLCA1 as the founding member of a new eukaryotic metzincin family, here termed CLCAsins, with unique regulatory mechanisms.

molecular biology↗

bioRxiv2025

The role of Akkermansia muciniphila sulfatases in colonic mucinutilisation

Akkermansia muciniphila, an obligate mucin degrader, is a major member of the human colonic microbiota and has been associated positive health outcomes. Mucins are complex glycoproteins that contain heavily sulfated O-glycans and form the protective colonic mucus layer. Bacterial carbohydrate sulfatases are required to metabolise these heavily sulfated mucin glycans and excessive bacterial foraging has been associated with several diseases. Sulfatases have been linked with inflammatory bowel disease, making these microbiota enzymes potential drug targets. A. muciniphila expresses carbohydrate sulfatases that can act on colonic mucins yet their roles in its metabolism remain opaque. Our data reveal that A. muciniphila requires glycopeptides/protein forms of colonic mucin for metabolism and its sulfatases have unique adaptations compared to Bacteroides species. Localisation studies reveal that desulfation of N-acetyl-D-glucosamine, but not D-galactose, is exclusively periplasmic. A cell surface sulfatase has a novel carbohydrate binding module that binds to colonic mucin. This paints a contrasting picture of sulfated mucin metabolism by Akkermansia muciniphila versus Bacteroides species. These data will be important for understanding the contexts for Akkermansia muciniphilas positive health correlations.

biochemistry↗