Nucleotide binding as an allosteric regulatory mechanism for Akkermansia muciniphila ß-N-acetylhexosaminidase Am2136.

ß-N-acetylhexosaminidases (EC3.2.1.52), which belong to the glycosyl hydrolase family GH20, are important enzymes for oligosaccharides modification. Numerous microbial ß-N-acetylhexosaminidases have been investigated for applications in biology, biomedicine and biotechnology. Akkermansia muciniphila is an anaerobic intestinal commensal bacterium which possesses specific ß-N-acetylhexosaminidases for gut mucosal layer colonization and mucin degradation. In this study, we assessed the in vitro mucin glycan cleavage activity of the A. muciniphila ß-N-acetylhexosaminidase Am2136 and demonstrated its ability that hydrolyzing the ß-linkages joining N-acetylglucosamine to a wide variety of aglycone residues, which indicated that Am2136 may be a generalist ß-N-acetylhexosaminidase. Structural and enzyme activity assay experiments allowed us to probe the essential function of the inter-domain interactions in ß23-ß33. Importantly, we revealed that the hydrolysis activity of Am2136 was enhanced by nucleotides. We further speculated that this activation mechanism might be associated with the conformational motions between domain III and IV. To our knowledge, this is the first report of nucleotide effector regulated ß-N-acetylhexosaminidase, to reveal its novel biological functions. These findings contribute to understanding the distinct properties within the GH20 family and lay a certain foundation to develop controllable glycan hydrolyzing catalysts.Abbreviations: OD600 - optical cell densities at 600 nm; LB - Luria-Bertani; IPTG - isopropyl ß-D-1-thiogalactopyranoside; PMSF - phenylmethanesulfonyl fluoride; rmsd - root mean square deviation; GlcNAc - N-acetyl-ß-D-glucosamine; GalNAc - N-acetyl-ß-D-galactosamine; Gal - galactose.

Structural analysis of the sulfatase AmAS from Akkermansia muciniphila.

Akkermansia muciniphila, an anaerobic Gram-negative bacterium, is a major intestinal commensal bacterium that can modulate the host immune response. It colonizes the mucosal layer and produces nutrients for the gut mucosa and other commensal bacteria. It is believed that mucin desulfation is the rate-limiting step in the mucin-degradation process, and bacterial sulfatases that carry out mucin desulfation have been well studied. However, little is known about the structural characteristics of A. muciniphila sulfatases. Here, the crystal structure of the premature form of the A. muciniphila sulfatase AmAS was determined. Structural analysis combined with docking experiments defined the critical active-site residues that are responsible for catalysis. The loop regions I-V were proposed to be essential for substrate binding. Structure-based sequence alignment and structural superposition allow further elucidation of how different subclasses of formylglycine-dependent sulfatases (FGly sulfatases) adopt the same catalytic mechanism but exhibit diverse substrate specificities. These results advance the understanding of the substrate-recognition mechanisms of A. muciniphila FGly-type sulfatases. Structural variations around the active sites account for the different substrate-binding properties. These results will enhance the understanding of the roles of bacterial sulfatases in the metabolism of glycans and host-microbe interactions in the human gut environment.