Crystal structure of the GalNAc/Gal-specific agglutinin from the phytopathogenic ascomycete Sclerotinia sclerotiorum reveals novel adaptation of a beta-trefoil domain

International audienceA lectin from the phytopathogenic ascomycete Sclerotinia sclerotiorum that shares only weak sequence similarity with characterized fungal lectins has recently been identified. S. sclerotiorum agglutinin (SSA) is a homodimeric protein consisting of two identical subunits of ∼ 17 kDa and displays specificity primarily towards Gal/GalNAc. Glycan array screening indicates that SSA readily interacts with Gal/GalNAc-bearing glycan chains. The crystal structures of SSA in the ligand-free form and in complex with the Gal-β1,3-GalNAc (T-antigen) disaccharide have been determined at 1.6 and 1.97 Å resolution, respectively. SSA adopts a β-trefoil domain as previously identified for other carbohydrate-binding proteins of the ricin B-like lectin superfamily and accommodates terminal non-reducing galactosyl and N-acetylgalactosaminyl glycans. Unlike other structurally related lectins, SSA contains a single carbohydrate-binding site at site α. SSA reveals a novel dimeric assembly markedly dissimilar to those described earlier for ricin-type lectins. The present structure exemplifies the adaptability of the β-trefoil domain in the evolution of fungal lectins

Lytic xylan oxidases from wood-decay fungi unlock biomass degradation

Wood biomass is the most abundant feedstock envisioned for the development of modern biorefineries. However, the cost-ef-fective conversion of this form of biomass into commodity products is limited by its resistance to enzymatic degradation. Here we describe a new family of fungal lytic polysaccharide monooxygenases (LPMOs) prevalent among white-rot and brown-rot basidiomycetes that is active on xylans—a recalcitrant polysaccharide abundant in wood biomass. Two AA14 LPMO members from the white-rot fungus Pycnoporus coccineus substantially increase the efficiency of wood saccharification through oxida-tive cleavage of highly refractory xylan-coated cellulose fibers. The discovery of this unique enzyme activity advances our knowledge on the degradation of woody biomass in nature and offers an innovative solution for improving enzyme cocktails for biorefinery applications

The long-awaited structure of human fucosidase FucA1 opens novel avenues for the treatment of fucosidosis

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Des glycosidases bactériennes pour du sang universel

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Glycosyltransferases, glycoside hydrolases: surprise, surprise!

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Snapshots of ADp-ribose bound to Getah virus macro domain reveal an intriguing choreography

International audienceAlphaviruses are (re-)emerging arboviruses of public health concern. The nsP3 gene product is one of the key players during viral replication. NsP3 comprises three domains: a macro domain, a zincbinding domain and a hypervariable region. the macro domain is essential at both early and late stages of the replication cycle through ADp-ribose (ADpr) binding and de-ADp-ribosylation of host proteins. However, both its specific role and the precise molecular mechanism of de-ADP-ribosylation across specific viral families remains to be elucidated. Here we investigate by X-ray crystallography the mechanism of ADPr reactivity in the active site of Getah virus macro domain, which displays a peculiar substitution of one of the conserved residues in the catalytic loop. ADpr adopts distinct poses including a covalent bond between the c′′1 of the ADPr and a conserved Togaviridae-specific cysteine. These different poses observed for ADPr may represent snapshots of the de-ADP-ribosylation mechanism, highlighting residues to be further characterised

The Three-dimensional Structure of Invertase (β-Fructosidase) from Thermotoga maritima Reveals a Bimodular Arrangement and an Evolutionary Relationship between Retaining and Inverting Glycosidases

International audienceThermotoga maritima invertase (-fructosidase) hy-drolyzes sucrose to release fructose and glucose, which are major carbon and energy sources for both pro-karyotes and eukaryotes. The name " invertase " was given to this enzyme over a century ago, because the 1:1 mixture of glucose and fructose that it produces was named " invert sugar. " Despite its name, the enzyme operates with a mechanism leading to the retention of the anomeric configuration at the site of cleavage. The enzyme belongs to family GH32 of the sequence-based classification of glycosidases. The crystal structure, determined at 2-Å resolution, reveals two modules, namely a five-bladed-propeller with structural similarity to the-propeller structures of glycosidase from families GH43 and GH68 connected to a-sandwich module. Three carboxylates at the bottom of a deep, negatively charged funnel-shaped depression of the-propeller are essential for catalysis and function as nucleophile, general acid, and transition state stabilizer, respectively. The catalytic machinery of invertase is perfectly super-imposable to that of the enzymes of families GH43 and GH68. The variation in the position of the furanose ring at the site of cleavage explains the different mechanisms evident in families GH32 and GH68 (retaining) and GH43 (inverting) furanosidases. Invertase, the-D-fructofuranosidase (EC 3.2.1.26) that cleaves sucrose into fructose and glucose is one of the earliest discovered enzymes. It was isolated in the second half of the 19th century, and its name was coined because the enzyme produces " invert " sugar, which is a 1:1 mixture of dextrorota-tory D-glucose and levorotatory D-fructose (1). Because of its chemical structure, sucrose can be cleaved by either-glucosi-dase or-fructofuranosidase activity. Koshland and Stein established that invertase is a-fructofuranosidase by performing the reaction in 18 O-labeled water and determining the 1

Crystal Structure of Streptococcus pneumoniae N -Acetylglucosamine-1-phosphate Uridyltransferase Bound to Acetyl-coenzyme A Reveals a Novel Active Site Architecture

International audienceThe bifunctional bacterial enzymeN-acetyl-glucosamine-1-phosphate uridyltransferase (GlmU) catalyzes the two-step formation of UDP-GlcNAc, a fundamental precursor in bacterial cell wall biosynthesis. With the emergence of new resistance mechanisms against β-lactam and glycopeptide antibiotics, the biosynthetic pathway of UDP-GlcNAc represents an attractive target for drug design of new antibacterial agents. The crystal structures of Streptococcus pneumoniae GlmU in unbound form, in complex with acetyl-coenzyme A (AcCoA) and in complex with both AcCoA and the end product UDP-GlcNAc, have been determined and refined to 2.3, 2.5, and 1.75 Å, respectively. TheS. pneumoniae GlmU molecule is organized in two separate domains connected via a long α-helical linker and associates as a trimer, with the 50-Å-long left-handed β-helix (LβH) C-terminal domains packed against each other in a parallel fashion and the C-terminal region extended far away from the LβH core and exchanged with the β-helix from a neighboring subunit in the trimer. AcCoA binding induces the formation of a long and narrow tunnel, enclosed between two adjacent LβH domains and the interchanged C-terminal region of the third subunit, giving rise to an original active site architecture at the junction of three subunits