Recombinant Salmonella paratyphi B NADH-quinone oxidoreductase subunit K (nuoK)

What is NADH-quinone oxidoreductase subunit K (nuoK) in Salmonella paratyphi B?

NADH-quinone oxidoreductase subunit K (nuoK) is a membrane protein component of the NADH dehydrogenase I complex (NDH-1) in Salmonella paratyphi B, functioning as part of the bacterial respiratory chain electron transport system . The protein is encoded by the nuoK gene (locus name SPAB_00659) and has been classified with the Enzyme Commission number EC 1.6.99.5, indicating its role in oxidoreduction reactions . NuoK participates in the transfer of electrons from NADH to quinones, contributing to the creation of a proton gradient across the bacterial membrane, which is essential for ATP synthesis and cellular energy production. The full amino acid sequence of nuoK from Salmonella paratyphi B (strain ATCC BAA-1250 / SPB7) has been identified as: MIPLTHGLILAAILFVLGLTGLVIRRNLLFMLIGLEIMINAS ALAFVVAGSYWGQTDGQVMYILAISLAAAEASIGLALLLQLHRRRQNLNIDSVSEMRG . It is important to note that nuoK functions within the context of different Salmonella paratyphi B biotypes, including the sensu stricto biotype, which causes paratyphoid fever, and the Java biotype, which is associated with gastroenteritis .

How should recombinant Salmonella paratyphi B nuoK protein be stored for optimal stability?

The optimal storage conditions for recombinant Salmonella paratyphi B nuoK protein involve a careful balance of temperature, buffer composition, and handling practices to maintain structural integrity and biological activity . For standard laboratory storage, recombinant nuoK should be kept at -20°C in an appropriate buffer system, typically a Tris-based buffer containing 50% glycerol that has been optimized specifically for this protein . For extended preservation periods, it is recommended to store the protein at either -20°C or preferably -80°C to minimize molecular degradation and maintain functional integrity . Researchers should strictly avoid repeated freezing and thawing cycles which can significantly accelerate protein denaturation and loss of enzymatic activity. For ongoing experiments requiring regular access to the protein, working aliquots can be safely maintained at 4°C for up to one week, though activity should be regularly monitored . When preparing storage buffers, consideration should be given to maintaining physiologically relevant pH and ionic strength to preserve the native conformation of the protein, particularly important for membrane proteins like nuoK that contain hydrophobic domains.

What is the phylogenetic relationship between different Salmonella Paratyphi B strains?

The phylogenetic relationships among Salmonella Paratyphi B strains reveal complex evolutionary patterns characterized by distinct genetic lineages and geographic clustering . Advanced whole-genome sequencing studies have employed sophisticated bioinformatic approaches including Parsnp alignment and Gubbins algorithms to detect recombination regions in the core genome, enabling more accurate phylogenetic reconstructions . Time-resolved phylogeny analyses conducted using BEAST (Bayesian Evolutionary Analysis Sampling Trees) with recombination-filtered single-nucleotide polymorphisms (SNPs) have estimated mutation rates of approximately 1.7 SNP/genome/year (95% CI 1.44–2.0 SNP/genome/year) for Salmonella Paratyphi B strains, comparable to other S. enterica serovars despite their distinct ecological niches . Principal component analysis of accessory genome components has identified at least two major clusters: Cluster I, which groups historical strains with European isolates and some Latin American strains, and Cluster II, which exclusively contains Latin American strains and is associated with a prophage sequence similar to Salmonella phage SEN34 . Further genomic analyses of plasmid composition have revealed additional clustering patterns (Clusters I-IV) associated with different plasmid types, including IncI1, IncHI2, and COLRNAI plasmids, which cross geographical boundaries and provide insights into horizontal gene transfer patterns among these strains .

How does antimicrobial resistance develop in Salmonella Paratyphi B, and what are the genetic mechanisms involved?

Antimicrobial resistance in Salmonella Paratyphi B has emerged through complex genetic mechanisms involving both chromosomal elements and mobile genetic determinants, contributing to a concerning rise in multidrug-resistant isolates . The Salmonella genomic island 1 (SGI1), a 43-kb DNA segment originally characterized in Salmonella Typhimurium DT104, has been identified as a major contributor to multidrug resistance in S. Paratyphi B dT+ strains in Canada and globally . This genetic island harbors genes conferring the pentaresistance phenotype (ampicillin, chloramphenicol, streptomycin, sulfonamide, and tetracycline, collectively abbreviated as ACSSuT) . Nucleotide sequencing of SGI1 has revealed 44 open reading frames, some showing homology to genes associated with plasmid transfer, suggesting its potential plasmidic origin and capacity for horizontal transmission between bacterial populations . The worldwide dissemination of resistant strains harboring SGI1 has led researchers to hypothesize that this genetic element may provide selective advantages beyond antimicrobial resistance . Additionally, plasmid-mediated resistance has been documented in S. Paratyphi B var. Java sequence type 28 (ST28) strains, with principal component analysis identifying distinct clusters associated with specific plasmid types, including IncI1 plasmids (cluster I), IncHI2 plasmids (cluster II), COLRNAI plasmids (cluster III), and combinations of IncI1 and IncHI2 plasmids (cluster IV) . These findings underscore the complex interplay between chromosomal and plasmid-mediated resistance mechanisms in S. Paratyphi B, contributing to the rapid emergence and dissemination of multidrug-resistant strains that pose significant clinical challenges.

What are the metabolomic signatures associated with Salmonella Paratyphi infections?

Salmonella Paratyphi infections generate distinctive metabolomic signatures that can be leveraged for diagnostic applications and to understand host-pathogen interactions during enteric fever . Two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC/TOFMS) analysis of plasma from patients with Salmonella infections has identified 695 individual metabolite peaks, demonstrating the complex metabolic perturbations induced during infection . Supervised pattern recognition techniques applied to these metabolomic data have revealed highly significant and reproducible metabolite profiles that can effectively distinguish S. Typhi cases, S. Paratyphi A cases, and uninfected controls . Researchers have determined that a combination of just six metabolites can accurately define the etiological agent, representing a potential breakthrough for rapid diagnostic applications in regions where enteric fever is endemic . These serovar-specific systemic biomarkers not only provide diagnostic utility but also offer valuable insights into the biological mechanisms underlying the pathogenesis of different Salmonella serovars, including S. Paratyphi B. Although the specific metabolomic signatures for S. Paratyphi B have not been as extensively characterized as those for S. Typhi and S. Paratyphi A, the established methodological framework provides a robust approach for extending these investigations to S. Paratyphi B infections, potentially revealing unique metabolic adaptations associated with both the sensu stricto and Java biotypes .

What approaches are being explored for vaccine development against Salmonella Paratyphi B?

Vaccine development against Salmonella Paratyphi B has progressed significantly with the exploration of live attenuated vaccine candidates that demonstrate cross-protection against both major biotypes . Researchers have successfully developed a live attenuated Salmonella enterica serovar Paratyphi B vaccine that confers protection in mouse models challenged with both S. Paratyphi B sensu stricto (causative agent of enteric fever) and S. Paratyphi B Java (associated with gastroenteritis) . This dual protection capability is particularly valuable given the antigenic similarities yet distinct clinical manifestations of these two biotypes. The rationale for developing such vaccines has been strengthened by observations that the emergence of new conjugate vaccines targeting other enteric fever serovars could potentially create an ecological niche that might be filled by S. Paratyphi B, leading to increased incidence of these infections . Comparative genomics approaches have informed the rational design of these vaccine candidates by identifying conserved antigens and virulence factors that can elicit protective immune responses against both biotypes . Although the current global incidence of invasive S. Paratyphi B sensu stricto infections remains relatively low, the development of effective vaccines represents a proactive strategy in the comprehensive control of Salmonella infections and anticipates potential epidemiological shifts that might occur in response to vaccination programs targeting other Salmonella serovars .

What are the optimal conditions for expression and purification of recombinant Salmonella paratyphi B nuoK?

The expression and purification of recombinant Salmonella paratyphi B nuoK requires specialized approaches due to its hydrophobic nature and membrane-embedded characteristics . Researchers typically employ bacterial expression systems such as Escherichia coli strains specifically designed for membrane protein expression, including C41(DE3), C43(DE3), or Lemo21(DE3), which are engineered to tolerate the potential toxicity associated with overexpression of membrane proteins. The expression vector selection should incorporate strong, inducible promoters (such as T7) and appropriate fusion tags that facilitate detection and purification while minimizing interference with protein folding and function . Common fusion partners include histidine tags, which enable metal affinity chromatography, or larger solubility-enhancing partners such as maltose-binding protein (MBP) or glutathione S-transferase (GST) that may improve membrane protein solubility. The expression conditions should be carefully optimized, typically involving lower temperatures (16-25°C) and reduced inducer concentrations to promote proper membrane integration and folding. For purification, a multi-step approach is recommended, beginning with membrane fraction isolation through differential centrifugation, followed by solubilization using mild detergents such as n-dodecyl-β-D-maltopyranoside (DDM) or lauryl maltose neopentyl glycol (LMNG) . Subsequent purification typically employs a combination of affinity chromatography, ion exchange, and size exclusion techniques, maintaining detergent concentrations above critical micelle concentration throughout to prevent protein aggregation.

What techniques are available for studying protein-protein interactions involving nuoK in the respiratory complex?

The investigation of protein-protein interactions involving nuoK within the respiratory complex requires sophisticated techniques capable of capturing both stable and transient associations in their native membrane environment . Cross-linking mass spectrometry (XL-MS) represents a powerful approach that can capture spatial relationships between nuoK and neighboring proteins by introducing covalent bonds between proximal amino acid residues, followed by enzymatic digestion and mass spectrometric analysis to identify the cross-linked peptides. Blue native polyacrylamide gel electrophoresis (BN-PAGE) enables the separation of intact membrane protein complexes under non-denaturing conditions, preserving physiologically relevant interactions and allowing subsequent immunoblotting or mass spectrometry to confirm the presence of nuoK within specific respiratory subcomplexes. Förster resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) techniques provide opportunities to study dynamic interactions in living bacterial cells by tagging nuoK and potential interaction partners with appropriate fluorophores or luciferase/fluorophore pairs, respectively. Cryo-electron microscopy (cryo-EM) has revolutionized structural biology of membrane protein complexes and can reveal the precise positioning of nuoK within the respiratory complex architecture at near-atomic resolution, providing insights into both structural arrangements and functional implications of these interactions. Co-immunoprecipitation followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) allows researchers to pull down nuoK along with its interaction partners using specific antibodies, followed by identification of the complete interactome, though this approach requires careful optimization for membrane proteins to maintain native interactions.

Table: Key Characteristics of Salmonella paratyphi B NADH-quinone oxidoreductase subunit K (nuoK)