Salmonella YqiC exerts its function through an oligomeric state.

Protein oligomerization occurs frequently both in vitro and in vivo, with specific functionalities associated with different oligomeric states. The YqiC protein from Salmonella Typhimurium forms a homotrimer through its C-terminal coiled-coil domain, and the protein is closely linked to the colonization and invasion of the bacteria to the host cells. To elucidate the importance of the oligomeric state of YqiC in vivo and its relation with bacterial infection, we mutated crucial residues in YqiC's coiled-coil region and confirmed the loss of trimer formation using chemical crosslinking and size exclusion chromatography coupled with multiple angle light scattering (SEC-MALS) techniques. The yqiC-knockout strain complemented with mutant YqiC showed significantly reduced colonization and invasion of Salmonella to host cells, demonstrating the critical role of YqiC oligomerization in bacterial pathogenesis. Furthermore, we conducted a protein-protein interaction study of YqiC using a pulled-down assay coupled with mass spectrometry analysis to investigate the protein's role in bacterial virulence. The results reveal that YqiC interacts with subunits of Complex II of the electron transport chain (SdhA and SdhB) and the ß-subunit of F0 F1 -ATP synthase. These interactions suggest that YqiC may modulate the energy production of Salmonella and subsequently affect the assembly of crucial virulence factors, such as flagella. Overall, our findings provide new insights into the molecular mechanisms of YqiC's role in S. Typhimurium pathogenesis and suggest potential therapeutic targets for bacterial infections.

Effects of colonization-associated gene yqiC on global transcriptome, cellular respiration, and oxidative stress in Salmonella Typhimurium.

BACKGROUND: yqiC is required for colonizing the Salmonella enterica serovar Typhimurium (S. Typhimurium) in human cells; however, how yqiC regulates nontyphoidal Salmonella (NTS) genes to influence bacteria-host interactions remains unclear. METHODS: The global transcriptomes of S. Typhimurium yqiC-deleted mutant (ΔyqiC) and its wild-type strain SL1344 after 2 h of in vitro infection with Caco-2 cells were obtained through RNA sequencing to conduct comparisons and identify major yqiC-regulated genes, particularly those involved in Salmonella pathogenicity islands (SPIs), ubiquinone and menaquinone biosynthesis, electron transportation chains (ETCs), and carbohydrate/energy metabolism. A Seahorse XFp Analyzer and assays of NADH/NAD+ and H2O2 were used to compare oxygen consumption and extracellular acidification, glycolysis parameters, adenosine triphosphate (ATP) generation, NADH/NAD+ ratios, and H2O2 production between ΔyqiC and SL1344. RESULTS: After S. Typhimurium interacts with Caco-2 cells, yqiC represses gene upregulation in aspartate carbamoyl transferase, type 1 fimbriae, and iron-sulfur assembly, and it is required for expressing ilvB operon, flagellin, tdcABCD, and dmsAB. Furthermore, yqiC is required for expressing mainly SPI-1 genes and specific SPI-4, SPI-5, and SPI-6 genes; however, it diversely regulates SPI-2 and SPI-3 gene expression. yqiC significantly contributes to menD expression in menaquinone biosynthesis. A Kyoto Encyclopedia of Genes and Genomes analysis revealed the extensive association of yqiC with carbohydrate and energy metabolism. yqiC contributes to ATP generation, and the analyzer results demonstrate that yqiC is required for maintaining cellular respiration and metabolic potential under energy stress and for achieving glycolysis, glycolytic capacity, and glycolytic reserve. yqiC is also required for expressing ndh, cydA, nuoE, and sdhB but suppresses cyoC upregulation in the ETC of aerobically and anaerobically grown S. Typhimurium; priming with Caco-2 cells caused a reversed regulation of yiqC toward upregulation in these ETC complex genes. Furthermore, yqiC is required for maintaining NADH/NAD+ redox status and H2O2 production. CONCLUSIONS: Specific unreported genes that were considerably regulated by the colonization-associated gene yqiC in NTS were identified, and the key role and tentative mechanisms of yqiC in the extensive modulation of virulence factors, SPIs, ubiquinone and menaquinone biosynthesis, ETCs, glycolysis, and oxidative stress were discovered.

Genotypic Diversity of Ciprofloxacin Nonsusceptibility and Its Relationship with Minimum Inhibitory Concentrations in Nontyphoidal Salmonella Clinical Isolates in Taiwan.

This study analyzed the genetic diversity of ciprofloxacin (CIP) nonsusceptibility and the relationship between two major mechanisms and minimum inhibitory concentrations (MICs) of CIP in nontyphoidal Salmonella (NTS). Chromosomal mutations in quinolone resistance-determining regions (QRDRs) and plasmid-mediated quinolone resistance (PMQR) genes were searched from ResFinder, ARG-ANNOT, and PubMed for designing the sequencing regions in gyrA, gyrB, parC, and parE, and the 13 polymerase chain reactions for PMQR genes. We found that QRDR mutations were detected in gyrA (82.1%), parC (59.0%), and parE (20.5%) but not in gyrB among the 39 isolates. Five of the 13 PMQR genes were identified, including oqxA (28.2%), oqxB (28.2%), qnrS (18.0%), aac(6')-Ib-cr (10.3%), and qnrB (5.1%), which correlated with the MICs of CIP within 0.25-2 µg/mL, and it was found that oxqAB contributed more than qnr genes to increase the MICs. All the isolates contained either QRDR mutations (53.8%), PMQR genes (15.4%), or both (30.8%). QRDR mutations (84.6%) were more commonly detected than PMQR genes (46.2%). QRDR mutation numbers were significantly associated with MICs (p < 0.001). Double mutations in gyrA and parC determined high CIP resistance (MICs ≥ 4 µg/mL). PMQR genes contributed to intermediate to low CIP resistance (MICs 0.25-2 µg/mL), thus providing insights into mechanisms underlying CIP resistance.

Role of wzxE in Salmonella Typhimurium lipopolysaccharide biosynthesis and interleukin-8 secretion regulation in human intestinal epithelial cells.

In Salmonella Typhimurium (S. Typhimurium), lipopolysaccharide (LPS) anchored on the bacterial outer membrane is a major immune stimulus that can broadly activate immune cells and induce innate immune responses. wzxE is involved in bacterial LPS biosynthesis but has rarely been reported in Salmonella; wzxE encodes a flipase that can flip the precursor of LPS across the membrane into the periplasm space. Our preliminary data showed that the wzxE transposon mutant of S. Typhimurium could not significantly adhere to and invade into HEp-2 cells, but the mechanism remains unknown. In this study, we infected human LS174T, Caco-2, HeLa, and THP-1 cells with the wild-type S. Typhimurium strain SL1344, its wzxE mutant, and its complemented strain. wzxE depletion significantly attenuated bacterial adhesion and internalization in the four cell types. In addition, the postinfectious production of interleukin-8 (IL-8) was significantly decreased in the Caco-2 cells infected with the wzxE mutant. Bacterial LPS stained with polymyxin B probe also exhibited a reduced signal in the wzxE mutant. The silver staining of purified LPS demonstrated a significant reduction of the O-antigen (OAg) chain in the wzxE mutant. To confirm the role of OAg in the wzxE mutant during infection, we treated the HT-29 cells with the S. Typhimurium strain SL1344, its wzxE mutant, and their purified LPS, which revealed significantly decreased IL-8 secretion in the HT-29 cells treated with purified LPS from the wzxE mutant and with the wzxE mutant. In conclusion, wzxE mediates LPS biosynthesis and plays a major role in bacterial pathogenesis by regulating OAg flipping.

Thermodynamic analysis of remote substrate binding energy in 3α-hydroxysteroid dehydrogenase/carbonyl reductase catalysis.

The binding energy of enzyme and substrate is used to lower the activation energy for the catalytic reaction. 3α-HSD/CR uses remote binding interactions to accelerate the reaction of androsterone with NAD+. Here, we examine the enthalpic and entropic components of the remote binding energy in the 3α-HSD/CR-catalyzed reaction of NAD+ with androsterone versus the substrate analogs, 2-decalol and cyclohexanol, by analyzing the temperature-dependent kinetic parameters through steady-state kinetics. The effects of temperature on kcat/Km for 3α-HSD/CR acting on androsterone, 2-decalol, and cyclohexanol show the reactions are entropically favorable but enthalpically unfavorable. Thermodynamic analysis from the temperature-dependent values of Km and kcat shows the binding of the E-NAD+ complex with either 2-decalol or cyclohexanol to form the ternary complex is endothermic and entropy-driven, and the subsequent conversion to the transition state is both enthalpically and entropically unfavorable. Hence, solvation entropy may play an important role in the binding process through both the desolvation of the solute molecules and the release of bound water molecules from the active site into bulk solvent. As compared to the thermodynamic parameters of 3α-HSD/CR acting on cyclohexanol, the hydrophobic interaction of the B-ring of steroids with the active site of 3α-HSD/CR contributes to catalysis by increasing exclusively the entropy of activation (ΔTΔS‡â€¯= 1.8 kcal/mol), while the BCD-ring of androsterone significantly lowers ΔΔH‡ by 10.4 kcal/mol with a slight entropic penalty of -1.9 kcal/mol. Therefore, the remote non-reacting sites of androsterone may induce a conformational change of the substrate binding loop with an entropic cost for better interaction with the transition state to decrease the enthalpy of activation, significantly increasing catalytic efficiency.

Contribution of remote substrate binding energy to the enzymatic rate acceleration for 3α-hydroxysteroid dehydrogenase/carbonyl reductase.

3α-Hydroxysteroid dehydrogenase/carbonyl reductase (3α-HSD/CR) catalyzes the oxidation of androsterone with NAD+ to form androstanedione and NADH with the rate limiting step being the release of NADH. In this study, we elucidate the role of remote substrate binding interactions contributing to the rate enhancement by 3α-HSD/CR through steady-state kinetic studies with the truncated substrate analogs. No enzyme activity was detected for methanol, ethanol, and 2-propanol, which lack the steroid scaffold of androsterone, implying that the steroid scaffold plays an important role in enzyme catalytic specificity. As compared to cyclohexanol, the activity for 2-decalol, androstenol, and androsterone increases by 0.9-, 90-, and 200-fold in kcat, and 37-, 1.9 × 106-, and 1.8 × 106-fold in kcat/KB, respectively. The rate limiting step is hydride transfer for 3α-HSD/CR catalyzing the reaction of cyclohexanol with NAD+ based on the observed rapid equilibrium ordered mechanism and equal deuterium isotope effects of 3.9 on V and V/K for cyclohexanol. The kcat/KB value results in ΔG‡ of 14.7, 12.6, 6.2, and 6.2 kcal/mol for the 3α-HSD/CR catalyzed reaction of cyclohexanol, 2-decalol, androstenol, and androsterone, respectively. Thus, the uniform binding energy from the B-ring of steroids with the active site of 3α-HSD/CR equally contributes 2.1 kcal/mol to stabilize both the transition state and ground state of the ternary complex, leading to the similarity in kcat for 2-decalol and cyclohexanol. Differential binding interactions of the remote BCD-ring and CD-ring of androsterone with the active site of 3α-HSD/CR contribute 8.5 and 6.4 kcal/mol to the stabilization of the transition state, respectively. The removal of the carbonyl group at C17 of androsterone has small effects on catalysis. Both uniform and differential binding energies from the remote sites of androsterone compared to cyclohexanol contribute to the 3α-HSD/CR catalysis, resulting in the increases in kcat and kcat/KB.