Mucins are glycoproteins located on the cell surfaces of animal gastrointestinal tracts. Mucins separate host tissues from microbial pathogens and are instrumental for host gut health. Here, we provide evidence that mucin degradation in the gut can be mediated by mucinolysomes, defined as extracellular multi-enzyme complexes specializing in mucin degradation. We computationally predict the presence of mucinolysomes across 63 metagenome-assembled genomes (MAGs) and two isolated genomes of anaerobic Limousia bacteria, including seven MAGs from human samples of six countries. All 65 genomes were found to display core mucinolysome components, consisting of 3~6 scaffoldins (containing up to 12 cohesin modules) and up to 22 dockerin-containing mucin-degrading CAZymes (carbohydrate active enzymes). The organization of mucinolysomes allows the assembly of up to 24 CAZymes in the same complex. We validated that a cultivated Limousia strain ET540 from chicken cecum can support growth on mucins as its sole carbon source, triggering the expression of most mucinolysome-related genes, including both scaffoldins and CAZymes. We also confirmed their assembly into a multi-enzyme complex by validating the cohesin-dockerin interactions among most of the mucinolysome proteins, using AlphaFold3. While mucinolysome-encoding Limousia have low abundance in different animal hosts, their abundance and prevalence are higher in farm animals than in humans, highlighting their important role in livestock gut ecosystems. Our findings reveal a novel mechanism of mucin degradation and provide a framework to explore microbial contributions to gut health and host-microbe interactions across species.
Akresi et al. (Wed,) studied this question.
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