Typhoidal and non-typhoidal Salmonelleae (NTS) cause typhoid fever and gastroenteritis, respectively, in humans. Salmonella typhoid toxin contributes to typhoid disease progression and chronic infection, but little is known about the role of its NTS ortholog. We found that typhoid toxin and its NTS ortholog induce different clinical presentations. The PltB subunit of each toxin exhibits different glycan-binding preferences that correlate with glycan expression profiles of host cells targeted by each bacterium at the primary infection or intoxication sites. Through co-crystal structures of PltB subunits bound to specific glycan receptor moieties, we show that they induce markedly different glycan-binding preferences and virulence outcomes. Furthermore, immunization with the NTS S. Javiana or its toxin offers cross-reactive protection against lethal-dose typhoid toxin challenge. Cumulatively, these results offer insights into the evolution of host adaptations in Salmonella AB toxins, their cell and tissue tropisms, and the design for improved typhoid vaccines and therapeutics.

Although a reduced expression of nm23 has been shown to correlate with a high metastatic potential in some human cancers, in colorectal cancers, conflicting data have been reported. As

Antibiotic-resistant S. Typhi secretes typhoid toxin despite antibiotic treatment MAb targeting the receptor-binding or nuclease subunits neutralizes typhoid toxin TyTx11 makes nuclease CdtB inactive by causing catalytic-site conformational change Toxin-neutralizing epitopes identified are conserved across S. Typhi clinical isolates

Typhoid toxin is an A 2 B 5 toxin secreted from Salmonella Typhi-infected cells during human infection and is suggested to contribute to typhoid disease progression and the establishment of chronic infection. To deliver the enzymatic 'A' subunits of the toxin to the site of action in host cells, the receptor-binding 'B' subunit PltB binds to the trisaccharide glycan receptor moieties terminated in N-acetylneuraminic acid (Neu5Ac) that is α2-3 or α2-6 linked to the underlying disaccharide, galactose (Gal) and N-acetylglucosamine (GlcNAc). Neu5Ac is present in both unmodified and modified forms, with 9-O-acetylated Neu5Ac being the most common modification in humans. Here we show that host cells associated with typhoid toxin-mediated clinical signs express both unmodified and 9-O-acetylated glycan receptor moieties. We found that PltB binds to 9-O-acetylated α2-3 glycan receptor moieties with a markedly increased affinity, while the binding affinity to 9-O-acetylated α2-6 glycans is only slightly higher, as compared to the affinities of PltB to the unmodified counterparts, respectively. We also present X-ray co-crystal structures of PltB bound to related glycan moieties, which supports the different effects of 9-O-acetylated α2-3 and α2-6 glycan receptor moieties on the toxin binding. Lastly, we demonstrate that the cells exclusively expressing unmodified glycan receptor moieties are less susceptible to typhoid toxin than the cells expressing 9-O-acetylated counterparts, although typhoid toxin intoxicates both cells. These results reveal a fine-tuning mechanism of a bacterial toxin that exploits specific chemical modifications of its glycan receptor moieties for virulence and provide useful insights into the development of therapeutics against typhoid fever.The Gram-negative rod-shaped bacteria Salmonella enterica serovar Typhi (S. enterica serovar Typhi or S. Typhi) is the cause of the life-threatening disease typhoid fever. Many millions of people including children under the age of five are affected by this infectious disease. Molecular mechanisms underlying typhoid disease progression and the establishment of chronic infection important for the transmission of this human-adapted pathogen are incompletely understood, but typhoid toxin, one of the virulence factors of S. Typhi, is suggested to contribute to these processes. Typhoid toxin consists of three functionally distinct subunits: two enzymatic 'A' subunits important for intoxicating host cells after the delivery into host cells and one homopentamer of receptor-binding 'B' subunit important for the delivery of the toxin into host cells. Typhoid toxin 'B' subunit recognizes specific three-sugar structures decorating the host cell surface, whose terminal sugar called N-acetylneuraminic acid (Neu5Ac) can be present in unmodified or modified forms. The modified Neu5Ac possesses additional chemical groups, with 9-O-acetylation being the most frequently found modification in humans. This study analyzes glycan expression profiles of primary tissues and cells assoc...

Highlights d Antibodies targeting glycan-receptor binding B subunits can be split into two classes d The two classes are grouped by their epitope locations on the B subunit homopentamer d B homopentamers act similar to heteropentamers due to their skewed A subunit positioning d The two antibody classes exhibit significantly different neutralizing efficacies

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Copper(i) N-heterocyclic carbene (CuNHC) complexes are more catalytically active than traditional transition metal salts for the cyclopropenation of internal alkynylsilanes and diazoacetate compounds. A series of 1,2,3-trisubstituted and 1,2,3,3-tetrasubstituted cyclopropenylsilane compounds were isolated in good overall yields. An interesting regioselective and chemodivergent reaction pathway was also observed to furnish a tetra-substituted furan for an electron-rich donor/acceptor diazoacetate. Finally, a practical synthesis of a cyclopropenyl-containing starting material that is useful for bioorthogonal chemistry is also described.

CPAF (chlamydial protease-like activity factor) is a Chlamydia trachomatis protease that is translocated into the host cytosol during infection. CPAF activity results in dampened host inflammation signaling, cytoskeletal remodeling, and suppressed neutrophil activation. Although CPAF is an emerging antivirulence target, its catalytic mechanism has been unexplored to date. Steady state kinetic parameters were obtained for recombinant CPAF with vimentin-derived peptide substrates using a high-performance liquid chromatography-based discontinuous assay (k cat = 45 ± 0.6 s −1 ; k cat /K m = 0.37 ± 0.02 μM −1 s −1 ) or a new fluorescence-based continuous assay (k cat = 23 ± 0.7 s −1 ; k cat /K m = 0.29 ± 0.03 μM −1 s −1 ). Residues H105, S499, E558, and newly identified D103 were found to be indispensable for autoproteolytic processing by mutagenesis, while participation of C500 was ruled out despite its proximity to the S499 nucleophile. Pre-steady state kinetics indicated a burst kinetic profile, with fast acylation (k acyl = 110 ± 2 s −1 ) followed by slower, partially rate-limiting deacylation (k deacyl = 57 ± 1 s −1 ). Both k cat − and k cat /K m −pH profiles showed single acidic limb ionizations with pK a values of 6.2 ± 0.1 and 6.5 ± 0.1, respectively. A forward solvent deuterium kinetic isotope effect of 2.6 ± 0.1 was observed for D 2 O k cat app , but a unity effect was found for D 2 O k cat /K m app . The k cat proton inventory was linear, indicating transfer of a single proton in the rate-determining transition state, most likely from H105. Collectively, these data provide support for the classification of CPAF as a serine protease and provide a mechanistic foundation for the future design of inhibitors.