| 1. |
- Luis, Ana S., et al.
(författare)
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Sulfated glycan recognition by carbohydrate sulfatases of the human gut microbiota.
- 2022
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Ingår i: Nature chemical biology. - : Springer Science and Business Media LLC. - 1552-4469 .- 1552-4450. ; 18:8, s. 841-849
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Tidskriftsartikel (refereegranskat)abstract
- Sulfated glycans are ubiquitous nutrient sources for microbial communities that have coevolved with eukaryotic hosts. Bacteria metabolize sulfated glycans by deploying carbohydrate sulfatases that remove sulfate esters. Despite the biological importance of sulfatases, the mechanisms underlying their ability to recognize their glycan substrate remain poorly understood. Here, we use structural biology to determine how sulfatases from the human gut microbiota recognize sulfated glycans. We reveal seven new carbohydrate sulfatase structures spanning four S1 sulfatase subfamilies. Structures of S1_16 and S1_46 represent novel structures of these subfamilies. Structures of S1_11 and S1_15 demonstrate how non-conserved regions of the protein drive specificity toward related but distinct glycan targets. Collectively, these data reveal that carbohydrate sulfatases are highly selective for the glycan component of their substrate. These data provide new approaches for probing sulfated glycan metabolism while revealing the roles carbohydrate sulfatases play in host glycan catabolism.
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| 2. |
- Hsieh, Samantha, et al.
(författare)
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Polysaccharide Capsules Equip the Human Symbiont Bacteroides thetaiotaomicron to Modulate Immune Responses to a Dominant Antigen in the Intestine
- 2020
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Ingår i: Journal of Immunology. - : The American Association of Immunologists. - 1550-6606 .- 0022-1767. ; 204:4, s. 1035-1046
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Tidskriftsartikel (refereegranskat)abstract
- Bacteria express multiple diverse capsular polysaccharides (CPSs) for protection against environmental and host factors, including the host immune system. Using a mouse TCR transgenic CD4+ T cell, BθOM, that is specific for B. thetaiotaomicron and a complete set of single CPS-expressing B. thetaiotaomicron strains, we ask whether CPSs can modify the immune responses to specific bacterial Ags. Acapsular B. thetaiotaomicron, which lacks all B. thetaiotaomicron CPSs, stimulated BθOM T cells more strongly than wild-type B. thetaiotaomicron Despite similar levels of BθOM Ag expression, many single CPS-expressing B. thetaiotaomicron strains were antistimulatory and weakly activated BθOM T cells, but a few strains were prostimulatory and strongly activated BθOM T cells just as well or better than an acapsular strain. B. thetaiotaomicron strains that expressed an antistimulatory CPS blocked Ag delivery to the immune system, which could be rescued by Fc receptor-dependent Ab opsonization. All single CPS-expressing B. thetaiotaomicron strains stimulated the innate immune system to skew toward M1 macrophages and release inflammatory cytokines in an MyD88-dependent manner, with antistimulatory CPS activating the innate immune system in a weaker manner than prostimulatory CPS. The expression of antistimulatory versus prostimulatory CPSs on outer membrane vesicles also regulated immune responses. Moreover, antistimulatory and prostimulatory single CPS-expressing B. thetaiotaomicron strains regulated the activation of Ag-specific and polyclonal T cells as well as clearance of dominant Ag in vivo. These studies establish that the immune responses to specific bacterial Ags can be modulated by a diverse set of CPSs.
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| 3. |
- Lindstad, Lars J., et al.
(författare)
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Human Gut Faecalibacterium prausnitzii Deploys a Highly Efficient Conserved System To Cross-Feed on beta-Mannan-Derived Oligosaccharides
- 2021
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Ingår i: mBio. - : American Society for Microbiology. - 2161-2129 .- 2150-7511. ; 12:3
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Tidskriftsartikel (refereegranskat)abstract
- beta-Mannans are hemicelluloses that are abundant in modern diets as components in seed endosperms and common additives in processed food. Currently, the collective understanding of beta-mannan saccharification in the human colon is limited to a few keystone species, which presumably liberate low-molecular-weight mannooligosaccharide fragments that become directly available to the surrounding microbial community. Here, we show that a dominant butyrate producer in the human gut, Faecalibacterium prausnitzii, is able to acquire and degrade various beta-mannooligosaccharides (beta-MOS), which are derived by the primary mannanolytic activity of neighboring gut microbiota. Detailed biochemical analyses of selected protein components from their two beta-MOS utilization loci (F. prausnitzii beta-MOS utilization loci [FpMULs]) supported a concerted model whereby the imported beta-MOS are stepwise disassembled intracellularly by highly adapted enzymes. Coculturing experiments of F. prausnitzii with the primary degraders Bacteroides ovatus and Roseburia intestinalis on polymeric beta-mannan resulted in syntrophic growth, thus confirming the high efficiency of the FpMULs' uptake system. Genomic comparison with human F. prausnitzii strains and analyses of 2,441 public human metagenomes revealed that FpMULs are highly conserved and distributed worldwide. Together, our results provide a significant advance in the knowledge of beta-mannan metabolism and the degree to which its degradation is mediated by cross-feeding interactions between prominent beneficial microbes in the human gut. IMPORTANCE Commensal butyrate-producing bacteria belonging to the Firmicutes phylum are abundant in the human gut and are crucial for maintaining health. Currently, insight is lacking into how they target otherwise indigestible dietary fibers and into the trophic interactions they establish with other glycan degraders in the competitive gut environment. By combining cultivation, genomic, and detailed biochemical analyses, this work reveals the mechanism enabling F. prausnitzii, as a model Ruminococcaceae within Firmicutes, to cross-feed and access beta-mannan-derived oligosaccharides released in the gut ecosystem by the action of primary degraders. A comprehensive survey of human gut metagenomes shows that FpMULs are ubiquitous in human populations globally, highlighting the importance of microbial metabolism of beta-mannans/beta-MOS as a common dietary component. Our findings provide a mechanistic understanding of the beta-MOS utilization capability by F. prausnitzii that may be exploited to select dietary formulations specifically boosting this beneficial symbiont, and thus butyrate production, in the gut.
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