The sialate O-acetylesterase EstA from gut Bacteroidetes species enables sialidase-mediated cross-species foraging of 9-O-acetylated sialoglycans

Abstract

The gut harbors many symbiotic, commensal, and pathogenic microbes that break down and metabolize host carbohydrates. Sialic acids are prominent outermost carbohydrates on host glycoproteins called mucins and protect underlying glycan chains from enzymatic degradation. Sialidases produced by some members of the colonic microbiota can promote the expansion of several potential pathogens (e.g. Clostridium difficile, Salmonella, and Escherichia coli) that do not produce sialidases. O-Acetyl ester modifications of sialic acids help resist the action of many sialidases and are present at high levels in the mammalian colon. However, some gut bacteria, in turn, produce sialylate-O-acetylesterases to remove them. Here, we investigated O-acetyl ester removal and sialic acid degradation by Bacteroidetes sialate-O-acetylesterases and sialidases, respectively, and subsequent utilization of host sialic acids by both commensal and pathogenic E. coli strains. In vitro foraging studies demonstrated that sialidase-dependent E. coli growth on mucin is enabled by Bacteroides EstA, a sialate O-acetylesterase acting on glycosidically linked sialylate-O-acetylesterase substrates, particularly at neutral pH. Biochemical studies suggested that spontaneous migration of O-acetyl esters on the sialic acid side chain, which can occur at colonic pH, may serve as a switch controlling EstA-assisted sialic acid liberation. Specifically, EstA did not act on O-acetyl esters in their initial 7-position. However, following migration to the 9-position, glycans with O-acetyl esters became susceptible to the sequential actions of bacterial esterases and sialidases. We conclude that EstA specifically unlocks the nutritive potential of 9-O-acetylated mucus sialic acids for foraging by bacteria that otherwise are prevented from accessing this carbon source.

Epithelial-microbial diplomacy: escalating border tensions drive inflammation in inflammatory bowel disease

“…[59][60][61][62] In fact, commensals such as Faecalibacterium prausnitzii rely on these mucin specialists to facilitate their colonization to the mucus layer. [63][64][65][66][67][68] Akkermansia muciniphila is a widely studied mucin specialist capable of tolerating the hypoxic environment near the epithelial surface and that utilizes hostderived proteins for survival. [69][70][71] A. muciniphila colonization increases mucin production and mucus thickness, and improves barrier function.…”

De-O-Acetylation of mucin-derived sialic acids by recombinant NanS-p esterases of Escherichia coli O157:H7 strain EDL933

“…In the human large intestine, commensal mucin-degrading species of the phyla Bacteroidetes, Firmicutes, Actinobacteria and Verrucomicrobia can cleave bound sialic acids from glycans by intrinsic sialidases, providing free nutritional sialic acids for sialidase-negative E. coli (Robinson et al, 2017;Tailford et al, 2015;Vimr et al, 2004). Sialidases are substrate-specific and the decoration of sialic acids with one or more O-acetyl residues prevents sialidases from enzymatic cleavage.…”

When Cultures Meet: The Landscape of “Social” Interactions between the Host and Its Indigenous Microbes

“…[65] In addition, some bacteria have been shown to thrive on host-derived epithelial cells and mucus; [66] the availability of niche-specific conditions, such as periepithelial oxygen gradients, supporting some microbial strains; [67,68] and protection from pathogenic invasion by host-derived factors such as antimicrobial peptide secretion, [69] mucus layer barrier function, [70] and IgA secretion. As such, mammalian commensals thrive on the specialized atmospheric and metabolic microenvironments created by their host.…”