Chitinolytic enzymes contribute to the pathogenicity of Aliivibrio salmonicida LFI1238 in the invasive phase of cold-water vibriosis

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Perdeuterated GbpA Enables Neutron Scattering Experiments of a Lytic Polysaccharide Monooxygenase

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Immunization with lytic polysaccharide monooxygenase CbpD induces protective immunity against Pseudomonas aeruginosa pneumonia

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A family of papain-like fungal chimerolectins with distinct Ca2+-dependent activation mechanism

An important function of fungal lectins is to protect their host. Marasmius oreades agglutinin (MOA) is toxic to nematodes and exerts its protective effect through protease activity. Its proteolytic function is associated with a papain-like dimerization domain. The closest homologue of MOA is Polyporus squamosus lectin 1a (PSL1a). Here, we probed PSL1a for catalytic activity and confirmed that it is a calcium-dependent cysteine protease, like MOA. The X-ray crystal structures of PSL1a (1.5 Å) and MOA (1.3 Å) in complex with calcium and the irreversible cysteine protease inhibitor E-64 elucidated the structural basis for their mechanism of action. The comparison with other calcium-dependent proteases (calpains, LapG) reveals a unique metal-dependent activation mechanism relying on a calcium-induced backbone shift and intradimer cooperation. Intriguingly, the enzymes appear to use a tyrosine-gating mechanism instead of pro-peptide processing. A search for potential MOA orthologues suggests the existence of a whole new family of fungal chimerolectins with these unique features

Virus-like immune defense protein in mushrooms

Fungi and plants do not have an adaptive immune system. Innate immunity serves as their sole defense, often based on carbohydrate recognition by lectins. In a twist of nature, as revealed by Sommer et al. (2018) in this issue of Structure, a conserved fungal immunoprotein adopts the shape of a miniature virus

Crystal structure of MOA in complex with a peptide fragment: A protease caught in flagranti

The Marasmius oreades agglutinin (MOA) is the holotype of an emerging family of fungal chimerolectins and an active Ca2+/Mn2+-dependent protease, which exhibits a unique papain-like fold with special active site features. Here we investigated the functional significance of the structural elements differentiating MOA from other papain-like cysteine proteases. X-ray crystal structures of MOA co-crystallized with two synthetic substrates reveal cleaved peptides bound to the catalytic site, corresponding to the final products of the proteolytic reaction. Anomalous diffraction data on crystals grown in the presence of calcium and manganese, cadmium or zinc resolve the calcium/manganese preference of MOA and elucidate the inhibitory roles of zinc and cadmium towards papain-like cysteine proteases in general. The reported structures, together with activity data of MOA active site variants, point to a conservation of the general proteolysis mechanism established for papain. Ultimately, the findings suggest that papain and the papain-like domain of MOA are the product of convergent evolution

Family of Papain-Like Fungal Chimerolectins with Distinct Ca²⁺-Dependent Activation Mechanism

An important function of fungal lectins is to protect their host. <i>Marasmius oreades</i> agglutinin (MOA) is toxic to nematodes and exerts its protective effect through protease activity. Its proteolytic function is associated with a papain-like dimerization domain. The closest homologue of MOA is <i>Polyporus squamosus</i> lectin 1a (PSL1a). Here, we probed PSL1a for catalytic activity and confirmed that it is a calcium-dependent cysteine protease, like MOA. The X-ray crystal structures of PSL1a (1.5 Å) and MOA (1.3 Å) in complex with calcium and the irreversible cysteine protease inhibitor E-64 elucidated the structural basis for their mechanism of action. The comparison with other calcium-dependent proteases (calpains, LapG) reveals a unique metal-dependent activation mechanism relying on a calcium-induced backbone shift and intradimer cooperation. Intriguingly, the enzymes appear to use a tyrosine-gating mechanism instead of pro-peptide processing. A search for potential MOA orthologues suggests the existence of a whole new family of fungal chimerolectins with these unique features

An Unusual Member of the Papain Superfamily: Mapping the Catalytic Cleft of the Marasmius oreades agglutinin (MOA) with a Caspase Inhibitor

Papain-like cysteine proteases (PLCPs) constitute the largest group of thiol-based protein degrading enzymes and are characterized by a highly conserved fold. They are found in bacteria, viruses, plants and animals and involved in a number of physiological and pathological processes, parasitic infections and host defense, making them interesting targets for drug design. The Marasmius oreades agglutinin (MOA) is a blood group B-specific fungal chimerolectin with calcium-dependent proteolytic activity. The proteolytic domain of MOA presents a unique structural arrangement, yet mimicking the main structural elements in known PLCPs. Here we present the X-ray crystal structure of MOA in complex with Z-VAD-fmk, an irreversible caspase inhibitor known to cross-react with PLCPs. The structural data allow modeling of the substrate binding geometry and mapping of the fundamental enzyme-substrate interactions. The new information consolidates MOA as a new, yet strongly atypical member of the papain superfamily. The reported complex is the first published structure of a PLCP in complex with the well characterized caspase inhibitor Z-VAD-fmk

Novel exported fusion enzymes with chorismate mutase and cyclohexadienyl dehydratase activity: Shikimate pathway enzymes teamed up in no man's land

Chorismate mutase (CM) and cyclohexadienyl dehydratase (CDT) catalyze two subsequent reactions in the intracellular biosynthesis of L-phenylalanine (Phe). Here, we report the discovery of novel and extremely rare bifunctional fusion enzymes, consisting of fused CM and CDT domains, which are exported from the cytoplasm. Such enzymes were found in only nine bacterial species belonging to non-pathogenic γ- or β-Proteobacteria. In γ-proteobacterial fusion enzymes, the CM domain is N-terminal to the CDT domain, whereas the order is inverted in β-Proteobacteria. The CM domains share 15% to 20% sequence identity with the AroQγ class CM holotype of Mycobacterium tuberculosis (∗MtCM), and the CDT domains 40% to 60% identity with the exported monofunctional enzyme of Pseudomonas aeruginosa (PheC). In vitro kinetics revealed a Kₘ <7 μM, much lower than for ∗MtCM, whereas kinetic parameters are similar for CDT domains and PheC. There is no feedback inhibition of CM or CDT by the pathway's end product Phe, and no catalytic benefit of the domain fusion compared with engineered single-domain constructs. The fusion enzymes of Aequoribacter fuscus, Janthinobacterium sp. HH01, and Duganella sacchari were crystallized and their structures refined to 1.6, 1.7, and 2.4 Å resolution, respectively. Neither the crystal structures nor the size-exclusion chromatography show evidence for substrate channeling or higher oligomeric structure that could account for the cooperation of CM and CDT active sites. The genetic neighborhood with genes encoding transporter and substrate binding proteins suggests that these exported bifunctional fusion enzymes may participate in signaling systems rather than in the biosynthesis of Phe.ISSN:0021-9258ISSN:1083-351

Polyporus squamosus Lectin 1a (PSL1a) Exhibits Cytotoxicity in Mammalian Cells by Disruption of Focal Adhesions, Inhibition of Protein Synthesis and Induction of Apoptosis.

PSL1a is a lectin from the mushroom Polyporus squamosus that binds to sialylated glycans and glycoconjugates with high specificity and selectivity. In addition to its N-terminal carbohydrate-binding domain, PSL1a possesses a Ca2+-dependent proteolytic activity in the C-terminal domain. In the present study, we demonstrate that PSL1a has cytotoxic effects on mammalian cancer cells, and we show that the cytotoxicity is dependent on the cysteine protease activity. PSL1a treatment leads to cell rounding and detachment from the substratum, concomitant with disruption of vinculin complexes in focal adhesions. We also demonstrate that PSL1a inhibits protein synthesis and induces apoptosis in HeLa cells, in a time- and concentration-dependent manner