Glycobiology and Extracellular Matrices
A previously uncharacterized O-glycopeptidase from Akkermansia muciniphila requires the Tn-antigen for cleavage of the peptide bond
Akkermansia muciniphila is key member of the human gut microbiota that impacts many features of host health. A major characteristic of this bacterium is its interaction with host mucin, which is abundant in the gut environment, and its ability to metabolize mucin as a nutrient source. The machinery deployed by A. muciniphila to enable this interaction appears to be extensive and sophisticated, yet it is incompletely defined. The uncharacterized protein AMUC_1438 is encoded by a gene that was previously shown to be upregulated when the bacterium is grown on mucin.The structure of a family 110 glycoside hydrolase provides insight into the hydrolysis of α-1,3-galactosidic linkages in λ-carrageenan and blood group antigens
α-Linked galactose is a common carbohydrate motif in nature that is processed by a variety of glycoside hydrolases from different families. Terminal Galα1–3Gal motifs are found as a defining feature of different blood group and tissue antigens, as well as the building block of the marine algal galactan λ-carrageenan. The blood group B antigen and linear α-Gal epitope can be processed by glycoside hydrolases in family GH110, whereas the presence of genes encoding GH110 enzymes in polysaccharide utilization loci from marine bacteria suggests a role in processing λ-carrageenan.Molecular analysis of an enigmatic Streptococcus pneumoniae virulence factor: The raffinose-family oligosaccharide utilization system
Streptococcus pneumoniae is an opportunistic respiratory pathogen that can spread to other body sites, including the ears, brain, and blood. The ability of this bacterium to break down, import, and metabolize a wide range of glycans is key to its virulence. Intriguingly, S. pneumoniae can utilize several plant oligosaccharides for growth in vitro, including raffinose-family oligosaccharides (RFOs, which are α-(1→6)-galactosyl extensions of sucrose). An RFO utilization locus has been identified in the pneumococcal genome; however, none of the proteins encoded by this locus have been biochemically characterized.Two complementary α-fucosidases from Streptococcus pneumoniae promote complete degradation of host-derived carbohydrate antigens
An important aspect of the interaction between the opportunistic bacterial pathogen Streptococcus pneumoniae and its human host is its ability to harvest host glycans. The pneumococcus can degrade a variety of complex glycans, including N- and O-linked glycans, glycosaminoglycans, and carbohydrate antigens, an ability that is tightly linked to the virulence of S. pneumoniae. Although S. pneumoniae is known to use a sophisticated enzyme machinery to attack the human glycome, how it copes with fucosylated glycans, which are primarily histo-blood group antigens, is largely unknown.Endo-fucoidan hydrolases from glycoside hydrolase family 107 (GH107) display structural and mechanistic similarities to α-l-fucosidases from GH29
Fucoidans are chemically complex and highly heterogeneous sulfated marine fucans from brown macro algae. Possessing a variety of physicochemical and biological activities, fucoidans are used as gelling and thickening agents in the food industry and have anticoagulant, antiviral, antitumor, antibacterial, and immune activities. Although fucoidan-depolymerizing enzymes have been identified, the molecular basis of their activity on these chemically complex polysaccharides remains largely uninvestigated.Properties of a family 56 carbohydrate-binding module and its role in the recognition and hydrolysis of β-1,3-glucan
BH0236 from Bacillus halodurans is a multimodular β-1,3-glucanase comprising an N-terminal family 81 glycoside hydrolase catalytic module, an internal family 6 carbohydrate-binding module (CBM) that binds the nonreducing end of β-1,3-glucan chains, and an uncharacterized C-terminal module classified into CBM family 56. Here, we determined that this latter CBM, BhCBM56, bound the soluble β-1,3-glucan laminarin with a dissociation constant (Kd) of ∼26 μm and displayed higher affinity for insoluble β-1,3-glucans with Kd values of ∼2–10 μm but lacked affinity for β-1,3-glucooligosaccharides.A Second β-Hexosaminidase Encoded in the Streptococcus pneumoniae Genome Provides an Expanded Biochemical Ability to Degrade Host Glycans
Background: The genome of Streptococcus pneumoniae encodes a second uncharacterized family 20 glycoside hydrolase.Results: GH20C displays activity on both terminal β-linked N-acetylglucosamine and N-acetylgalactosamine.Conclusion: GH20C is an enzyme able to cleave a wide variety of N-acetylhexosamine-terminating sugars.Significance: S. pneumoniae has the biochemical ability to act on a wide variety of sugars that it would encounter in the human body.Structural Analysis of a Family 101 Glycoside Hydrolase in Complex with Carbohydrates Reveals Insights into Its Mechanism
Background: The endo-α-d-N-acetylgalactosaminidase SpGH101 from Streptococcus pneumoniae hydrolyzes the O-linked T-antigen from proteins.Results: SpGH101 displays an unusual conformational change on substrate binding and a distinctive arrangement of its catalytic machinery.Conclusion: Substrate hydrolysis proceeds through a retaining mechanism with a proton shuttle.Significance: This is the first evidence of proton shuttle in a retaining glycoside hydrolase.
