The role of 9-O-acetylated glycan receptor moieties in the typhoid toxin binding and intoxication.

Typhoid toxin is an A2B5 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 Role of Typhoid Toxin in Salmonella Typhi Virulence
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Unlike many of the nontyphoidal Salmonella serovars such as S. Typhimurium that cause restricted gastroenteritis, Salmonella Typhi is unique in that it causes life-threatening typhoid fever in humans. Despite the vast difference in disease outcomes that S. Typhi and S. Typhimurium cause in humans, there are few genomic regions that are unique to S. Typhi. Of these regions, the most notable is the small locus encoding typhoid toxin, an AB toxin that has several distinct characteristics that contribute to S. Typhi's pathogenicity. As a result, typhoid toxin and its role in S. Typhi virulence have been studied in an effort to gain insight into potential treatment and prevention strategies. Given the rise of multidrug-resistant strains, research in this area has become increasingly important. This article discusses the current understanding of typhoid toxin and potential directions for future research endeavors in order to better understand the contribution of typhoid toxin to S. Typhi virulence.

Streptococcus mutans sortase A inhibitory metabolites from the flowers of Sophora japonica.

A new maltol derivative (2) along with three known maltol derivative (1) and flavonol glycosides (3 and 4) were isolated from the dried flowers of Sophora japonica. Based upon the results of combined spectroscopic methods, the structure of new compound (2) was determined to be maltol-3-O-(4'-O-cis-p-coumaroyl-6'-O-(3-hydroxy-3-methylglutaroyl))-ß-glucopyranoside, an isomer of 1. These compounds strongly inhibited the action of sortase A (SrtA) from Streptococcus mutans, a primary etiologic agent of human dental caries. The onset and magnitude of inhibition of the saliva-induced aggregation in S. mutans treated with compound 2 (4×IC50) were comparable to the behavior of untreated srtA-deletion mutant.

Salternamides A-D from a Halophilic Streptomyces sp. Actinobacterium.

Salternamides A-D (1-4), the first secondary metabolites discovered from saltern-derived actinomycetes, were isolated from a halophilic Streptomyces strain isolated from a saltern on Shinui Island in the Republic of Korea. The planar structures of the salternamides, which are new members of the manumycin family, were elucidated by a combination of spectroscopic analyses. The absolute configurations of the salternamides were determined by chemical and spectroscopic methods, including the modified Mosher's method, J-based configuration analysis, and circular dichroism spectroscopy. Salternamide A (1), which is the first chlorinated compound in the manumycin family, exhibited potent cytotoxicity against a human colon cancer cell line (HCT116) and a gastric cancer cell line (SNU638) with submicromolar IC50 values. Salternamides A and D were also determined to be weak Na(+)/K(+) ATPase inhibitors.

Amino Acid-Derived Metabolites from the Ascidian Aplidium sp.

Four new iodobenzene-containing dipeptides (1-4), a related bromotryptophan-containing dipeptide (5), and an iodophenethylamine (6) were isolated from the ascidian Aplidium sp. collected off the coast of Chuja-do, Korea. The structures of these novel compounds, designated as apliamides A-E (1-5) and apliamine A (6) were determined via combined spectroscopic analyses. The absolute configuration of the amino acid residue in 1 was determined by advanced Marfey's analysis. Several of these compounds exhibited moderate cytotoxicity and significant inhibition against Na+/K+-ATPase (4).

Bahamaolide A from the marine-derived Streptomyces sp. CNQ343 inhibits isocitrate lyase in Candida albicans.

Bahamaolide A, a new macrocyclic lactone isolated from the culture of marine actinomycete Streptomyces sp. CNQ343, was evaluated for its inhibitory activity toward isocitrate lyase (ICL) from Candida albicans. These studies led to the identification of bahamaolide A as a potent ICL inhibitor with IC50 value of 11.82 µM. The growth phenotype of ICL deletion mutants and quantitative RT-PCR analyses indicated that this compound inhibits the ICL mRNA expression in C. albicans under C2-carbon-utilizing conditions. The present data highlight the potential for bahamaolide A treatment of C. albicans infections via inhibition of ICL activity.

Lajollamycins, nitro group-bearing spiro-ß-lactone-γ-lactams obtained from a marine-derived Streptomyces sp.

Lajollamycins (1-4), each of which bears a spiro-ß-lactone-γ-lactam ring and a nitro-tetraene moiety, were obtained from a marine-derived Streptomyces strain isolated from the southern area of Jeju Island, Republic of Korea. The planar structures of the lajollamycins were elucidated on the basis of spectroscopic analyses by NMR, UV, IR, and MS. The absolute configuration of lajollamycin (1), the planar structure of which has been previously reported, was determined using J-based configuration analysis based on (1)H-(1)H and (1)H-(13)C coupling constants, as well as ROESY correlations, followed by the modified Mosher's method. The absolute configurations of lajollamycins B-D (2-4) were established by comparing their CD spectra with that of 1. The lajollamycins exhibited moderate inhibitory activity toward Candida albicans isocitrate lyase.

Suvanine sesterterpenes from a tropical sponge Coscinoderma sp. inhibit isocitrate lyase in the glyoxylate cycle.

The glyoxylate cycle is a sequence of anaplerotic reactions catalyzed by the key enzymes isocitrate lyase (ICL) and malate synthase (MLS). Mutants of Candida albicans lacking ICL are markedly less virulent in mice than the wild-type. Suvanine sesterterpenes (1-9) isolated from a tropical sponge Coscinoderma sp. were evaluated for their inhibitory activities toward recombinant ICL from C. albicans. These studies led to the identification of a potent ICL inhibitor, suvanine salt (2), which possesses a sodium counterion and displays an inhibitory concentration value (IC50) of 6.35 µM. The growth phenotype of ICL deletion mutants and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses indicated that compound 2 inhibits the ICL mRNA expression in C. albicans under C2-carbon-utilizing conditions. The present data highlight the potential for suvanine sesterterpenes treatment of C. albicans infections via inhibition of ICL activity.

Amino alcohols from the ascidian Pseudodistoma sp.

Seven new amino alcohol compounds, pseudoaminols A-G (1-7), were isolated from the ascidian Pseudodistoma sp. collected off the coast of Chuja-do, Korea. Structures of these new compounds were determined by analysis of the spectroscopic data and from chemical conversion. The presence of an N-carboxymethyl group in two of the new compounds (6 and 7) is unprecedented among amino alcohols. Several of these compounds exhibited moderate antimicrobial activity and cytotoxicity, as well as weak inhibitory activity toward Na+/K+-ATPase.

Antimicrobial properties of tomato juice and peptides against typhoidal Salmonella.

Tomatoes are readily available and affordable vegetables that offer a range of health benefits due to their bioactive molecules, such as antioxidants and antimicrobials. In contrast to the widely recognized antioxidant properties of tomatoes, their antimicrobial properties remain largely unexplored. Here, we present our findings on the antimicrobial properties of tomato juice and peptides, namely, tomato-derived antimicrobial peptides (tdAMPs), in relation to their effectiveness against typhoidal Salmonella. Our research has revealed that tomato juice demonstrates significant antimicrobial properties against Salmonella Typhi, a pathogen that specifically affects humans and is responsible for causing typhoid fever. By employing computational analysis of the tomato genome sequence, conducting molecular dynamics simulation, and performing functional analyses, we have successfully identified two tdAMPs, namely, tdAMP-1 and tdAMP-2. These tdAMPs have demonstrated potent antimicrobial properties by effectively disrupting bacterial membranes. The efficacy of tdAMP-2 is shown to be more effective than tdAMP-1. The efficacy of tdAMP-1 and tdAMP-2 has been demonstrated against drug-resistant S. Typhi, as well as hyper-capsular S. Typhi variants that possess hypervirulent characteristics, which are presently circulating in countries with endemicity. Tomato juice, along with the two tdAMPs, has demonstrated effectiveness against uropathogenic Escherichia coli as well. This underscores their potential as viable agents in combating certain Gram-negative pathogens. This study provides valuable insights into the development of effective and sustainable public health strategies that utilize tomato and its derivatives as lifestyle interventions.IMPORTANCEIn this study, we investigate the antimicrobial properties of tomato juice, the most widely consumed affordable vegetables, as well as tomato-derived antimicrobial peptides, in relation to their effectiveness against foodborne pathogens with an emphasis on Salmonella Typhi, a deadly human-specific pathogen.

Inhibition of yeast-to-hypha transition in Candida albicans by phorbasin H isolated from Phorbas sp.

Phorbasin H is a diterpene acid of a bisabolane-related skeletal class isolated from the marine sponge Phorbas sp. In this study, we examined whether phorbasin H acted as a yeast-to-hypha transition inhibitor of Candida albicans. Growth experiments suggest that this compound does not inhibit yeast cell growth but inhibits filamentous growth in C. albicans. Northern blot analysis of signaling pathway components indicated that phorbasin H inhibited the expression of mRNAs related to cAMP-Efg1 pathway. The exogenous addition of db-cAMP to C. albicans cells had no influence on the frequency of hyphal formation. The expression of hypha-specific HWP1 and ALS3 mRNAs, both of which are positively regulated by the important regulator of cell wall dynamics Efg1, was significantly inhibited by the addition of phorbasin H. This compound also reduced the ability of C. albicans cells to adhere in a dose-dependent manner. Our findings suggest that phorbasin H impacts the activity of the cAMP-Efg1 pathway, thus leading to an alteration of C. albicans morphology.

Beta-carboline alkaloids derived from the ascidian Synoicum sp.

Six ß-carboline alkaloids (1-6) of the eudistomin Y class were isolated from the Korean ascidian Synoicum sp. These compounds were chemically converted to a known compound, eudistomin Y(1) (7) and six new derivatives, designated eudistomins Y(8)-Y(13) (8-13). Several of these natural and synthetic compounds exhibited moderate to significant antimicrobial activity, weak cytotoxic activity, and inhibitory activities toward sortase A, isocitrate lyase, and Na(+)/K(+)-ATPase. Structure-activity relationships were also deduced.

Brominated aromatic furanones and related esters from the ascidian Synoicum sp.

Nine new compounds, tris-aromatic furanones (1, 2, 3a, 3b, and 4) and related bis-aromatic diesters (5a, 5b, 6a, and 6b), are described from the ascidian Synoicum sp. collected off the coast of Chuja-do, Korea. The structures of these compounds, designated as cadiolides E and G-I (1-4) and synoilides A and B (5 and 6), were determined by extensive spectroscopic analyses. The absolute configuration at the asymmetric center of cadiolide G (2) was assigned by ECD analysis. Of these new compounds, cadiolide I and the synoilides possess unprecedented carbon skeletons. Several of these compounds exhibited significant inhibition against diverse bacterial strains as well as moderate inhibition against the enzymes sortase A, isocitrate lyase, and Na(+)/K(+)-ATPase.

Acylated kaempferol glycosides from Laurus nobilis leaves and their inhibitory effects on Na+/K+-adenosine triphosphatase.

Na(+)/K(+)-adenosine triphosphatase (ATPase) inhibitors have considerable therapeutic potential against some heart diseases like congestive heart failure and cardiac arrhythmias. Through bioassay-guided separation of the leaf extract of Laurus nobilis, six acylated kaempferol glycosides (compounds 1-6) were isolated. Their structures were determined on the basis of spectroscopic analysis and comparison with reported data. All the isolates were subjected to in vitro bioassays to evaluate their inhibitory activities against Na(+)/K(+)-ATPase from porcine cerebral cortex and bacterial growth. These studies led to the identification of compounds 1-6 as potent Na(+)/K(+)-ATPase inhibitors, with IC(50) values in the range of 4.0 ± 0.1-10.4 ± 0.6 µM. These compounds also exhibited a broad spectrum of antibacterial activity. In particular, compounds 4 and 6 showed potent inhibitory activities against several bacterial strains, except Escherichia coli, with minimum inhibitory concentration (MIC) values in the range of 0.65-2.08 µg/mL. Thus, L. nobilis-derived acylated kaempferol glycosides may have a potential to be leads for the development of Na(+)/K(+) ATPase inhibitors (1-6) and antibacterial agents (4, 6).

Glycan-mediated molecular interactions in bacterial pathogenesis.

Glycans are expressed on the surface of nearly all host and bacterial cells. Not surprisingly, glycan-mediated molecular interactions play a vital role in bacterial pathogenesis and host responses against pathogens. Glycan-mediated host-pathogen interactions can benefit the pathogen, host, or both. Here, we discuss (i) bacterial glycans that play a critical role in bacterial colonization and/or immune evasion, (ii) host glycans that are utilized by bacteria for pathogenesis, and (iii) bacterial and host glycans involved in immune responses against pathogens. We further discuss (iv) opportunities and challenges for transforming these research findings into more effective antibacterial strategies, and (v) technological advances in glycoscience that have helped to accelerate progress in research. These studies collectively offer valuable insights into new perspectives on antibacterial strategies that may effectively tackle the drug-resistant pathogens that are rapidly spreading globally.

Actin depolymerizing effect of trisoxazole-containing macrolides.

Oxazole-containing macrolides (1-5) isolated from the marine sponge Chondrosia corticata were evaluated for their actin depolymerizing activities by monitoring fluorescent intensity of pyrene F-actin. These studies led to the identification of (19Z)-halichondramide (5) as a new actin depolymerizing agent. The actin depolymerizing activity by (19Z)-halichondramide (5) was four times more potent than that of halichondramide (1). Compounds 1 and 5 also have potent antifungal activity. The preliminary structure-activity relationship of these compounds is described to elucidate the essential structural requirements.

The structural basis of Salmonella A2B5 toxin neutralization by antibodies targeting the glycan-receptor binding subunits.

Many bacterial pathogens secrete A(2)B5 toxins comprising two functionally distinct yet complementary "A" and "B" subunits to benefit the pathogens during infection. The lectin-like pentameric B subunits recognize specific sets of host glycans to deliver the toxin into target host cells. Here, we offer the molecular mechanism by which neutralizing antibodies, which have the potential to bind to all glycan-receptor binding sites and thus completely inhibit toxin binding to host cells, are inhibited from exerting this action. Cryogenic electron microscopy (cryo-EM)-based analyses indicate that the skewed positioning of the toxin A subunit(s) toward one side of the toxin B pentamer inhibited neutralizing antibody binding to the laterally located epitopes, rendering some glycan-receptor binding sites that remained available for the toxin binding and endocytosis process, which is strikingly different from the counterpart antibodies recognizing the far side-located epitopes. These results highlight additional features of the toxin-antibody interactions and offer important insights into anti-toxin strategies.

Bromophenols as Candida albicans isocitrate lyase inhibitors.

A new series of bromophenols was synthesized by reactions of corresponding phenol analogs with bromine. The synthesized compounds were tested for inhibitory activity against isocitrate lyase (ICL) of Candida albicans and antimicrobial activity against gram-positive and, gram-negative bacteria and fungi. Among the synthesized bromophenols, bis(3-bromo-4,5-dihydroxyphenyl)methanone (11) and (3-bromo-4,5-dihydroxyphenyl)(2,3-dibromo-4,5-dihydroxyphenyl)methanone (12) displayed potent inhibitory activities against ICL, showing a stronger inhibitory effects than were found with natural bromophenol 1. The preliminary structure-activity relationships were investigated in order to determine the essential structural requirements for the inhibitory activities of these compounds against ICL of C. albicans.

Salmonella Typhoid Toxin PltB Subunit and Its Non-typhoidal Salmonella Ortholog Confer Differential Host Adaptation and Virulence.

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.

5-Hydroxyindole-type alkaloids, as Candida albicans isocitrate lyase inhibitors, from the tropical sponge Hyrtios sp.

Chemical investigations of the tropical marine sponge Hyrtios sp. have resulted in the isolation of a new alkaloid, 1-carboxy-6-hydroxy-3,4-dihydro-beta-carboline (1) together with the known metabolites, 6-hydroxy-3,4-dihydro-1-oxo-beta-carboline (2), 5-hydroxy-1H-indole-3-carboxylic acid methyl ester (3), serotonin (4), hyrtiosin A (5), 5-hydroxyindole-3-carbaldehyde (6), and hyrtiosin B (7). Their structures were elucidated on the basis of mass spectrometry and detailed 2D NMR spectroscopic data. Hyrtiosin B (7) displayed a potent inhibitory activity against isocitrate lyase (ICL) of Candida albicans with an IC(50) value of 89.0 microM.