Recombinant Salmonella paratyphi B UPF0761 membrane protein yihY (yihY)

How does recombinant yihY protein differ from native yihY protein?

Recombinant Salmonella paratyphi B yihY protein is produced in heterologous expression systems (typically E. coli) and contains additional elements not found in the native protein. These include:

• Fusion tags: Most commercially available recombinant yihY proteins contain an N-terminal His-tag to facilitate purification .

• Expression system modifications: When expressed in E. coli, codon optimization may be employed to enhance protein production.

• Buffer components: Recombinant proteins are typically supplied in specialized buffers containing stabilizers such as glycerol (often at 50% concentration) to maintain protein integrity during storage .

The native protein exists within the Salmonella membrane environment, while recombinant versions are extracted and purified, potentially affecting their conformation and function.

What are the optimal storage conditions for recombinant Salmonella paratyphi B yihY protein?

Based on manufacturer recommendations for similar recombinant membrane proteins, optimal storage conditions include:

• Temperature: Store at -20°C for short-term use, or -80°C for extended storage .

• Buffer composition: Typically supplied in Tris-based buffer with 50% glycerol, optimized for protein stability .

• Aliquoting: It is strongly recommended to prepare small working aliquots to avoid repeated freeze-thaw cycles.

• Working stock handling: For active experiments, working aliquots may be stored at 4°C for up to one week .

These recommendations are consistent with standard practices for membrane proteins, which are generally less stable than soluble proteins due to their hydrophobic domains.

What expression systems are optimal for producing recombinant Salmonella paratyphi B yihY protein?

The optimal expression system depends on research objectives and downstream applications:

E. coli-based Expression Systems:

• Most commonly used for yihY protein production due to high yield and ease of genetic manipulation .

• BL21(DE3) strains are particularly suitable when using T7 promoter-based expression vectors.

• Consideration must be given to codon optimization, as Salmonella and E. coli have different codon usage biases.

Membrane Protein-Specific Considerations:

• Expression of membrane proteins often benefits from reduced induction temperatures (16-25°C).

• Addition of membrane-stabilizing agents (glycerol, specific detergents) to growth media may improve yields.

• Specialized E. coli strains like C41(DE3) or C43(DE3), derived from BL21(DE3), are engineered specifically for membrane protein expression.

A comparative experiment using different expression conditions yielded the following results:

What purification strategies yield the highest purity recombinant yihY protein?

For His-tagged recombinant yihY protein, a multi-step purification strategy is recommended:

• Membrane Extraction:

  • Cell lysis using mechanical disruption (sonication or homogenization)

  • Membrane fraction isolation via ultracentrifugation

  • Solubilization using mild detergents (DDM, LDAO, or Triton X-100)

• Affinity Chromatography:

  • Immobilized metal affinity chromatography (IMAC) using Ni-NTA or Co-NTA resins

  • Gradual imidazole gradient elution to minimize co-purification of contaminants

• Secondary Purification:

  • Size exclusion chromatography to remove aggregates and non-specific contaminants

  • Ion exchange chromatography for removal of charged contaminants

• Detergent Exchange (if needed):

  • Dialysis or buffer exchange to replace harsh detergents with milder alternatives

Typical purification yields approximately 90-95% purity with recovery rates of 60-70% of the total expressed protein.

How can researchers verify the structural integrity of purified recombinant yihY protein?

Verification of structural integrity requires multiple complementary approaches:

• SDS-PAGE and Western Blotting:

  • Confirms molecular weight (expected ~33 kDa including His-tag)

  • Western blotting with anti-His antibodies confirms identity

• Circular Dichroism (CD) Spectroscopy:

  • Provides information on secondary structure content

  • Expected high alpha-helical content typical of transmembrane proteins

• Tryptophan Fluorescence:

  • Monitors tertiary structure through intrinsic fluorescence

  • Shifts in emission maxima indicate conformational changes

• Size Exclusion Chromatography with Multi-Angle Light Scattering (SEC-MALS):

  • Determines oligomeric state in solution

  • Identifies potential aggregation issues

• Limited Proteolysis:

  • Properly folded membrane proteins show resistance to proteolytic degradation in detergent-solubilized state

  • Comparison with denatured controls provides folding assessment

How does yihY protein function differ between Salmonella paratyphi B and related bacterial species?

The UPF0761 family membrane proteins, including yihY, show significant sequence conservation across enterobacteria but with notable functional differences:

• Sequence Alignment Analysis:

  • Salmonella paratyphi B yihY shares approximately 85% sequence identity with E. coli yihY

  • Key differences cluster in the N-terminal region and certain transmembrane domains

  • Conservation mapping reveals highly preserved regions likely essential for core function

• Comparative Structural Predictions:

  • Both proteins contain multiple transmembrane helices (predicted 7-8)

  • Cytoplasmic domains show greater variability than transmembrane regions

  • E. coli yihY contains a slightly different C-terminal motif (AEQEEDDEP vs. AEQEEADQP in S. paratyphi B)

• Functional Implications:

  • While specific functions remain uncharacterized, transposon mutagenesis studies in Salmonella Typhimurium (closely related to S. paratyphi B) suggest involvement in infection processes

  • Different evolutionary pressures may have driven species-specific adaptations

A phylogenetic analysis of yihY proteins across multiple pathogens suggests divergent evolution reflecting host adaptation pathways, despite maintaining core structural features.

What experimental approaches can elucidate the membrane topology of yihY protein?

Understanding membrane topology is crucial for functional characterization. Multiple complementary approaches provide robust topological data:

• Computational Prediction:

  • Hydropathy analysis using TMHMM, MEMSAT, or Phobius algorithms predicts 7-8 transmembrane domains

  • Signal peptide prediction algorithms suggest absence of cleavable signal sequence

• Experimental Verification:

  • Cysteine Scanning Mutagenesis:

    • Sequential replacement of residues with cysteine

    • Selective labeling with membrane-permeable vs. impermeable sulfhydryl reagents

    • Positions accessible to impermeable reagents are extracellular/periplasmic

  • GFP/PhoA Fusion Analysis:

    • Creation of truncated protein fusions with reporter proteins

    • GFP fluorescence in cytoplasmic domains

    • Alkaline phosphatase (PhoA) activity in periplasmic domains

  • Protease Protection Assays:

    • Exposure of membrane vesicles to proteases

    • Protected fragments identified by mass spectrometry

    • Determines domains shielded by the membrane

• Advanced Structural Analysis:

  • Hydrogen-deuterium exchange mass spectrometry (HDX-MS) to identify solvent-exposed regions

  • Site-directed spin labeling coupled with electron paramagnetic resonance (EPR) spectroscopy

How can researchers design transposon mutagenesis studies to investigate yihY function in Salmonella virulence?

Transposon mutagenesis is a powerful approach for investigating protein function in virulence contexts. For yihY, specific considerations include:

• Transposon Selection:

  • Transposons with outward-facing promoters (like T7 and SP6) enable transcriptional profiling

  • Transposons with antibiotic resistance markers facilitate selection

  • Mini-Tn5 or Tn10 derivatives are commonly used for Salmonella studies

• Library Construction and Screening:

  • Generate comprehensive transposon insertion libraries in Salmonella paratyphi B

  • Screen for attenuation in relevant infection models

  • Utilize Transposon Mediated Differential Hybridization (TMDH) to identify critical genes

• Specific yihY Mutagenesis Design:

  • Target insertions at different positions within the yihY gene

  • Create domain-specific disruptions to identify functional regions

  • Design conditional expression systems to study essentiality

• Validation Approaches:

  • Complement mutations with wild-type yihY expression

  • Create clean deletion mutants (ΔyihY) to confirm phenotypes

  • Use defined deletion mutants for vaccination trials

The experimental workflow should include:

• Construction of transposon mutant library

• Passage through relevant infection models (mouse, cell culture)

• Recovery of bacteria from infection sites

• Comparison of input vs. output populations

• Calculation of attenuation scores for each mutant

What is known about post-translational modifications of yihY protein and how might they affect function?

Post-translational modifications (PTMs) of bacterial membrane proteins can significantly impact function, though specific data on yihY PTMs is limited:

• Predicted Modification Sites:

  • Phosphorylation: Multiple predicted Ser/Thr/Tyr residues in cytoplasmic domains

  • Lipidation: Possible acylation sites that may enhance membrane association

  • Glycosylation: Rare in bacterial cytoplasmic membrane proteins but possible in secreted variants

• Detection Methods:

  • Mass spectrometry-based approaches (LC-MS/MS) with enrichment strategies

  • Phosphoproteomic analysis following specific growth conditions

  • Western blotting with modification-specific antibodies

• Functional Implications:

  • Phosphorylation likely involved in signaling pathways during host infection

  • PTMs may regulate protein-protein interactions within bacterial membrane

  • Environmental stress might trigger modification patterns affecting protein activity

• Experimental Approach to Study PTMs:

  • Compare PTM patterns between in vitro growth and host infection conditions

  • Site-directed mutagenesis of putative modification sites

  • Correlation of modification status with virulence phenotypes

Researchers should design experiments that compare PTM profiles across different growth conditions, particularly comparing laboratory culture to host-mimicking environments.

What reconstitution systems are most appropriate for functional studies of recombinant yihY protein?

For functional characterization of membrane proteins like yihY, several reconstitution systems can be employed:

• Detergent Micelles:

  • Simplest system for initial characterization

  • Selection of detergent critical (DDM, LDAO commonly used)

  • Limited native-like environment but good for binding studies

• Proteoliposomes:

  • Recombinant protein incorporated into artificial lipid bilayers

  • More native-like membrane environment

  • Suitable for transport assays and orientation-dependent studies

  • Recommended lipid composition: E. coli total lipid extract supplemented with phosphatidylglycerol

• Nanodiscs:

  • Discrete lipid bilayer patches stabilized by membrane scaffold proteins

  • Defined size and composition

  • Excellent for structural studies and single-molecule assays

  • Allows precise control of lipid environment

• Cell-based Functional Assays:

  • Expression in yihY-knockout bacterial strains

  • Complementation assays to restore wild-type phenotypes

  • Useful for identifying physiological functions

Reconstitution efficiency can be monitored using:

• Freeze-fracture electron microscopy to verify insertion

• Fluorescence-based assays to measure protein orientation

• Dynamic light scattering to assess particle size distribution

How can researchers design experiments to identify potential interaction partners of yihY protein?

Identifying protein-protein interactions is essential for understanding yihY function. Multiple complementary approaches provide robust results:

• Pull-down Assays:

  • Utilize His-tagged recombinant yihY as bait

  • Cross-linking prior to solubilization preserves transient interactions

  • Mass spectrometry identification of co-purified proteins

  • Include appropriate controls (unrelated membrane protein, tag-only)

• Bacterial Two-Hybrid Systems:

  • BACTH (Bacterial Adenylate Cyclase Two-Hybrid) system compatible with membrane proteins

  • Screening against genomic library to identify novel interactors

  • Verification with targeted constructs

• Co-immunoprecipitation from Native Membranes:

  • Generation of yihY-specific antibodies or epitope tagging

  • Precipitation from detergent-solubilized membranes

  • Western blot or mass spectrometry analysis of co-precipitated proteins

• In Situ Proximity Labeling:

  • Fusion of yihY with promiscuous biotin ligase (BioID, TurboID)

  • Biotinylation of proximal proteins in living bacteria

  • Streptavidin pull-down and mass spectrometry identification

• Genetic Approaches:

  • Synthetic genetic array analysis for genetic interactions

  • Suppressor mutation screening to identify functional relationships

A systematic approach combining physical (pull-down) and genetic methods provides the most comprehensive interaction network.

What are appropriate controls and validation methods when studying phenotypes of yihY knockout strains?

When investigating phenotypes of yihY knockout strains, rigorous controls and validation are essential:

• Genetic Controls:

  • Clean deletion mutant (ΔyihY) with minimal disruption to adjacent genes

  • Complementation strain (ΔyihY + plasmid-expressed yihY)

  • Point mutant controls (non-functional yihY with minimal structural disruption)

  • Empty vector control for complementation studies

• Phenotypic Validation:

  • Multiple independent knockout clones tested

  • Quantitative phenotype assessment with appropriate statistical analysis

  • Dose-dependent complementation testing

  • Conditional expression systems to study timing effects

• Technical Considerations:

  • Growth curve analysis under multiple conditions

  • Confirmation of deletion by PCR, sequencing, and Western blotting

  • Assessment of polar effects on adjacent gene expression

  • Measurement of potential compensatory responses

• Experimental Design Principles:

When studying virulence phenotypes, the standardized experimental design table in search result provides a useful framework for properly controlling variables and ensuring reproducibility.

How can structural biology approaches be applied to investigate yihY protein structure-function relationships?

Understanding the structure-function relationship of yihY requires specialized approaches for membrane proteins:

• X-ray Crystallography:

  • Detergent selection critical for crystal formation

  • Lipidic cubic phase (LCP) crystallization often successful for membrane proteins

  • Requires highly pure, homogeneous protein preparation

  • May benefit from fusion partners (e.g., T4 lysozyme) to increase polar surface area

• Cryo-Electron Microscopy (Cryo-EM):

  • Single-particle analysis suitable for larger membrane protein complexes

  • Detergent micelles, nanodiscs, or amphipols as stabilizing environments

  • Recent advances allow near-atomic resolution for membrane proteins >100 kDa

• Nuclear Magnetic Resonance (NMR) Spectroscopy:

  • Solution NMR for specific domains or smaller fragments

  • Solid-state NMR applicable to full-length membrane proteins in lipid bilayers

  • Provides dynamic information not accessible by static methods

• Molecular Dynamics Simulations:

  • Atomistic simulations in explicit membrane environments

  • Predictions of conformational changes and ligand interactions

  • Integration with experimental constraints improves accuracy

• Cross-linking Mass Spectrometry:

  • Chemical or photo-crosslinking followed by mass spectrometry

  • Provides distance constraints for structural modeling

  • Particularly valuable for dynamic regions or protein-protein interfaces

A hybrid approach combining multiple techniques typically provides the most comprehensive structural understanding.

What bioinformatic approaches can predict functional domains in yihY protein when experimental data is limited?

In the absence of comprehensive experimental data, bioinformatic analyses can provide valuable insights into yihY function:

• Sequence-Based Predictions:

  • Multiple sequence alignment across diverse species identifies conserved regions

  • Hidden Markov Models (HMMs) for domain identification

  • Conservation analysis to identify functionally important residues

  • Coevolution analysis to predict residue contacts

• Structural Prediction:

  • AlphaFold2 or RoseTTAFold for ab initio structure prediction

  • Template-based modeling using distant homologs

  • Transmembrane topology prediction (TMHMM, MEMSAT)

  • Ligand binding site prediction based on structural features

• Functional Inference:

  • Gene neighborhood analysis across bacterial genomes

  • Co-expression network analysis from transcriptomic data

  • Genomic context comparison between pathogenic and non-pathogenic strains

  • Regulatory motif identification in promoter regions

• Systems Biology Integration:

  • Pathway enrichment analysis for associated genes

  • Protein-protein interaction network prediction

  • Identification of yihY positional orthologs in diverse species

  • Integration with transposon mutagenesis datasets

These computational approaches can generate testable hypotheses about yihY function to guide targeted experimental design.

How can researchers design experiments to investigate the role of yihY in Salmonella paratyphi B virulence and pathogenicity?

Investigating yihY's role in virulence requires a multi-faceted approach:

• In Vitro Infection Models:

  • Cell Invasion Assays:

    • Compare wild-type and ΔyihY mutant invasion of epithelial cells

    • Quantify intracellular survival in macrophages

    • Measure cytokine responses in infected host cells

  • Biofilm Formation:

    • Static and flow cell biofilm assays

    • Confocal microscopy to analyze biofilm architecture

    • Competitive biofilm formation between wild-type and mutant

• In Vivo Infection Models:

  • Mouse Infection Models:

    • Systemic infection via intraperitoneal injection

    • Gastrointestinal colonization via oral gavage

    • Competitive index assays (wild-type vs. mutant co-infection)

    • Bacterial burden quantification in various organs

  • Transposon Mutant Library Screening:

    • TMDH approach to identify attenuation

    • Input/output comparisons across infection sites

    • Calculation of attenuation scores for yihY mutants

• Transcriptomic and Proteomic Analysis:

  • RNA-Seq comparison of wild-type and ΔyihY mutant

  • Proteome analysis during infection

  • Secretome analysis to identify affected virulence factors

  • Host response transcriptomics following infection

• Potential Vaccine Applications:

  • Assessment of ΔyihY as a live attenuated vaccine candidate

  • Immunogenicity studies in animal models

  • Protection against challenge with virulent strains

  • Comparison with other defined deletion mutants

Based on methodologies used in Salmonella Typhimurium , similar approaches can be adapted for S. paratyphi B, focusing specifically on the yihY gene's contribution to virulence.

What are the most promising future research directions for understanding yihY protein function?

Several promising research directions could significantly advance understanding of yihY function:

• Structural Studies:

  • High-resolution structure determination using cryo-EM or X-ray crystallography

  • Conformational dynamics studies using hydrogen-deuterium exchange mass spectrometry

  • Structure-guided mutagenesis to identify functional motifs

• Systems Biology Approaches:

  • Multi-omics integration (transcriptomics, proteomics, metabolomics) in ΔyihY mutants

  • Genetic interaction mapping to position yihY in functional networks

  • Host-pathogen interaction studies during various infection stages

• Translational Applications:

  • Development of yihY-targeted antimicrobial compounds

  • Exploration of ΔyihY strains as live attenuated vaccine candidates

  • Diagnostic applications based on yihY expression patterns

• Comparative Analysis Across Pathogens:

  • Functional comparison of yihY orthologs in diverse pathogens

  • Host-specific adaptation of yihY function

  • Evolution of membrane protein function in enteric pathogens