Unravelling the specificity and mechanism of sialic acid recognition by the gut symbiont Ruminococcus gnavus

Abstract

Ruminococcus gnavus is a human gut symbiont wherein the ability to degrade mucins is mediated by an intramolecular trans-sialidase (RgNanH). RgNanH comprises a GH33 catalytic domain and a sialic acid-binding carbohydrate-binding module (CBM40). Here we used glycan arrays, STD NMR, X-ray crystallography, mutagenesis and binding assays to determine the structure and function of RgNanH_CBM40 (RgCBM40). RgCBM40 displays the canonical CBM40 β-sandwich fold and broad specificity towards sialoglycans with millimolar binding affinity towards α2,3- or α2,6-sialyllactose. RgCBM40 binds to mucus produced by goblet cells and to purified mucins, providing direct evidence for a CBM40 as a novel bacterial mucus adhesin. Bioinformatics data show that RgCBM40 canonical type domains are widespread among Firmicutes. Furthermore, binding of R. gnavus ATCC 29149 to intestinal mucus is sialic acid mediated. Together, this study reveals novel features of CBMs which may contribute to the biogeography of symbiotic bacteria in the gut.

Mechanistic Insights Into the Cross-Feeding of Ruminococcus gnavus and Ruminococcus bromii on Host and Dietary Carbohydrates

“…Resource sharing is an important ecological feature of microbial communities living in the gut ( Tannock et al, 2012 ; Pereira and Berry, 2017 ; Centanni et al, 2018 ). The findings from our study suggest that, although R. gnavus strains are adapted to the mucosal environment owing to their mucin-foraging capacity ( Crost et al, 2013 , 2016 ; Tailford et al, 2015b ; Owen et al, 2017 ), their population dynamics within the colon may also be affected by the supply of dietary carbohydrates that reaches the large intestine undigested such as RS. Due to the high prevalence of R. bromii in the human colon, the hydrolysis of RS will cause the release of nutrients such as glucose or metabolites that may reach bacterial species within the mucus layer, potentially promoting the growth of other species to occur, thereby further underscoring the role of R. bromii as a keystone species.…”

A Sensitive and Rapid Method to Determine the Adhesion Capacity of Probiotics and Pathogenic Microorganisms to Human Gastrointestinal Mucins

“…For instance, the recently described adhesin domain, CBM40, present in the human gut symbionte Ruminococcus gnavus is specific towards sialoglycans with a millimolar binding affinity towards α2,3- or α2,6-sialyllactose. It also mediates adhesion to mucins [ 57 ]. In another study [ 58 ], the crucial role played by sialic acid residues bound to mucin O -glycans on the adhesion observed for two lactobacilli strains and one bifidobacteria strain was assessed.…”

Investigating host-microbiome interactions by droplet based microfluidics

“…However, biochemical studies can only be carried out when structurally defined substrates are available in large enough quantity. The difficulty of providing sufficient amounts of material for functional studies (hampered, e.g., by the high cost of human-derived substrates and the non-trivial effort involved in their synthesis) explains why only a handful of mechanisms for the foraging of gut bacteria on human glycans have been elucidated so far ( [15][16][17][18][19][20][21][22][23][24] reviewed in [13,25]). Among them, only a few are related to the metabolism of uncultured bacteria [17,18,24].…”