Recombinant Salmonella agona Probable intracellular septation protein A (yciB)

What is YciB and what is its structural characterization in Salmonella agona?

YciB (Probable intracellular septation protein A) is an inner membrane protein found in Salmonella agona and related bacteria. Structurally, YciB is a multi-pass transmembrane protein containing five transmembrane domains . The full amino acid sequence of Salmonella agona YciB consists of 179 residues and includes the sequence: MKQFLDFLPLVVFFAFYKLYDIYAATSALIVATAIVLIYSWVRYRKIEKMALITFVLVAVFGGLTLFFHNDEFIKWKVTVIYALFAGALLISQWVMKKPLIQRMLGKELALPQQVWSKLNLAWALFFIACGLANIYIAFWLPQNIWVNFKVFGLTALTLIFTLLSGVYIYRHLPQEDKS .

The membrane topology of YciB has been experimentally confirmed using a dual pho-lac reporter system in E. coli, verifying the predicted five-transmembrane domain structure . For research purposes, recombinant YciB from Salmonella agona (strain SL483) is available as a purified protein, typically stored in Tris-based buffer with 50% glycerol .

What are the key phenotypes associated with yciB deletion mutants?

Studies in E. coli have shown that deletion of yciB results in several distinct phenotypes:

• Increased susceptibility to low osmolarity conditions

• Reduced biofilm formation capacity

• Compromised cell envelope integrity, evidenced by increased sensitivity to antibiotics like vancomycin and detergents such as SDS in the presence of EDTA

These phenotypes become significantly more severe when yciB deletion is combined with deletion of dcrB, which encodes an inner membrane lipoprotein. The double mutant (ΔyciB ΔdcrB) shows synthetic lethality in low-salt medium, suggesting complementary roles in maintaining envelope integrity .

What experimental approaches are recommended for studying YciB localization?

To study YciB localization in bacterial cells, researchers should consider the following methodological approaches:

• Fluorescent protein fusion analysis: Creating YciB-GFP/YFP fusion proteins to visualize localization patterns using fluorescence microscopy. When designing these constructs, it's critical to ensure that the fluorescent tag doesn't disrupt the transmembrane topology of YciB.

• Membrane fractionation: Separate inner and outer membrane fractions using sucrose density gradient centrifugation followed by Western blot analysis with anti-YciB antibodies.

• Immunogold electron microscopy: Using gold-labeled antibodies against YciB for high-resolution localization within the membrane architecture.

• Bacterial two-hybrid system: This approach has successfully demonstrated that YciB interacts with various proteins involved in cell elongation and division . For this method:

  • Create fusion constructs of YciB with DNA-binding domain fragments

  • Create fusion constructs of potential interacting proteins with activation domain fragments

  • Co-transform into reporter strains and screen for positive interactions

  • Validate interactions using complementary methods such as co-immunoprecipitation

How do YciB and DcrB function synergistically in maintaining bacterial envelope integrity?

The synergistic relationship between YciB and DcrB is essential for maintaining bacterial envelope integrity through their roles in lipoprotein maturation and proper localization. Research findings indicate:

• Redundant functional roles: YciB and DcrB appear to have overlapping functions in maintaining cell envelope integrity, as evidenced by the synthetic lethality of the double mutant .

• Lipoprotein processing impact: In the ΔyciB ΔdcrB double mutant, the abundant outer membrane lipoprotein Lpp mislocalizes to the inner membrane where it forms toxic linkages to peptidoglycan . This mislocalization is due to inefficient lipid modification at the first step in lipoprotein maturation.

• Mechanistic basis: The aberrant localization of Lpp is attributed to attenuation in Lgt-mediated transacylation (phosphatidylglycerol:preprolipoprotein diacylglyceryl transferase activity) . The defect appears to be related to altered membrane fluidity rather than reduced phosphatidylglycerol levels.

• Temperature sensitivity: Notably, a ΔdcrB mutant alone shows poor viability at low temperatures, conditions that affect membrane fluidity, suggesting that DcrB becomes essential under conditions that challenge membrane homeostasis .

Methodologically, researchers can investigate this synergy through:

• Lipidomic analysis of membrane composition in single and double mutants

• Membrane fluidity measurements using fluorescence anisotropy techniques

• In vitro reconstitution of Lgt activity using purified components and membrane extracts from various mutants

What molecular mechanisms underlie YciB's role in lipoprotein maturation?

YciB appears to influence lipoprotein maturation indirectly by affecting membrane properties that impact the activity of lipoprotein processing enzymes. Key research findings suggest:

• Impact on Lgt function: In ΔyciB ΔdcrB cells, there is inefficient lipid modification by Lgt, which catalyzes the initial step in lipoprotein maturation (transfer of diacylglyceryl from phosphatidylglycerol to the lipobox cysteine) .

• Suppression mechanisms: The lethality of the ΔyciB ΔdcrB double mutant can be suppressed by:

  • Increased expression of Lgt

  • Deletion of lpp

  • Removal of Lpp-peptidoglycan linkages

• Envelope stress responses: Both Cpx and Rcs signaling systems are upregulated in the double mutant in response to envelope stress .

• Proposed model: YciB likely affects lipid homeostasis, altering membrane fluidity in ways that impact Lgt activity. The ΔyciB mutation may lead to lipid composition changes that simulate the physical effects of lower temperatures, making DcrB essential for lipoprotein maturation .

For researchers investigating these mechanisms, recommended approaches include:

• Lipidomic profiling of membrane phospholipid composition

• In vitro lipoprotein processing assays with membrane fractions

• Measurement of membrane physical properties (fluidity, thickness)

• Genetic suppressor screens to identify additional components

How can structural biology approaches contribute to understanding YciB function?

Structural biology approaches provide crucial insights into YciB's function by revealing:

• Structural homology: The crystal structure of DcrB (a functional partner of YciB) in Salmonella shares significant similarity with the mycobacterial periplasmic protein LpqN, which has been suggested to bind lipids and influence lipid transport . This suggests that exploring potential lipid-binding properties of YciB-associated proteins may be fruitful.

• Membrane topology determination: Experimental validation of YciB's predicted five transmembrane domains using techniques like the dual pho-lac reporter system has been successful .

• Protein-protein interaction interfaces: YciB interacts with various proteins involved in cell elongation and division . Structural studies can help map these interaction interfaces.

For researchers pursuing structural studies of YciB, consider:

• Expressing recombinant YciB with purification tags in expression systems optimized for membrane proteins

• Using detergent screening to identify optimal conditions for solubilization and purification

• Applying techniques like cryo-electron microscopy or X-ray crystallography for structural determination

• Performing site-directed mutagenesis of conserved residues to identify functionally important regions

What is the relationship between YciB function and Salmonella pathogenesis?

While direct evidence linking YciB to Salmonella virulence wasn't found in the provided search results, researchers can explore this connection based on these insights:

• Envelope integrity connection: YciB is involved in maintaining cell envelope integrity , which is crucial for bacterial survival during infection and resistance to host defense mechanisms.

• Salmonella outbreaks: Salmonella Agona has been implicated in significant outbreaks, including a 2017-2018 outbreak among infants in France associated with contaminated infant milk products . Understanding factors like YciB that affect membrane integrity may help explain persistence in manufacturing environments.

• Environmental persistence: The ability of Salmonella Agona to persist in dry food production environments for extended periods (as evidenced by outbreaks separated by years caused by the same strain) may be related to envelope properties influenced by proteins like YciB.

For researchers investigating YciB's potential role in pathogenesis, consider:

• Creating yciB deletion mutants in Salmonella agona and testing virulence in infection models

• Examining survival under conditions mimicking host environments (antimicrobial peptides, acidic pH, bile salts)

• Investigating potential contributions to persistence in food production environments

• Analyzing expression patterns of yciB during different stages of infection

What are the optimal conditions for expressing and purifying recombinant YciB?

Based on available information about recombinant YciB from Salmonella agona, researchers should consider the following methodological approach:

• Expression systems:

  • For structural studies: E. coli strains optimized for membrane protein expression (C41, C43) with inducible promoters

  • For functional studies: Expression in yciB knockout strains for complementation assays

• Purification strategy:

  • Affinity purification with appropriate tags (His-tag commonly used)

  • Solubilization in mild detergents (DDM, LMNG or equivalent)

  • Size exclusion chromatography for final purification

• Storage conditions:

  • Optimally stored in Tris-based buffer with 50% glycerol

  • Store at -20°C or -80°C for extended storage

  • Avoid repeated freeze-thaw cycles

  • Working aliquots can be stored at 4°C for up to one week

• Quality control:

  • Verify purity by SDS-PAGE

  • Confirm identity by mass spectrometry or western blotting

  • Assess proper folding using circular dichroism spectroscopy

How can interaction partners of YciB be systematically identified and validated?

To comprehensively identify and validate YciB interaction partners, researchers should employ multi-layered approaches:

• Screening for interactions:

  • Bacterial two-hybrid system: Successfully used to show YciB interacts with various proteins involved in cell elongation and division

  • Pull-down assays with tagged YciB followed by mass spectrometry

  • Co-immunoprecipitation with antibodies against YciB

• Validation methods:

  • Fluorescence resonance energy transfer (FRET) between YciB and candidate partners

  • Bimolecular fluorescence complementation (BiFC) in vivo

  • Surface plasmon resonance to measure binding kinetics of purified components

  • Genetic approaches: synthetic genetic interactions, suppressor screening

• Functional characterization:

  • Create deletion mutants of identified interaction partners

  • Test for phenocopy or synthetic effects with yciB mutations

  • Assess impact on lipoprotein maturation and membrane homeostasis

  • Map interaction domains through truncation and site-directed mutagenesis

• Localization studies:

  • Co-localization analysis using fluorescent protein fusions

  • Super-resolution microscopy to precisely map interaction sites

What comparative genomic approaches can reveal about YciB function across bacterial species?

Comparative genomic analyses provide valuable insights into the evolutionary conservation and potential functional importance of YciB:

• Ortholog identification and analysis:

  • Identify YciB orthologs across bacterial species using sequence similarity searches

  • Construct phylogenetic trees to understand evolutionary relationships

  • Analyze conservation patterns of specific domains or residues

  • Examine synteny (gene neighborhood conservation) across genomes

• Structure-function relationships:

  • Map conserved residues onto predicted structural models

  • Identify potentially functionally important motifs

  • Correlate sequence variation with differences in bacterial envelope organization

• Co-evolution analysis:

  • Identify proteins that show coordinated evolutionary patterns with YciB

  • Examine co-occurrence patterns of yciB and dcrB across bacterial genomes

  • Look for compensatory mutations that may indicate functional relationships

• Experimental verification:

  • Test complementation of E. coli yciB mutants with orthologs from different species

  • Compare phenotypes of yciB deletions across multiple bacterial species

  • Examine cross-species differences in interaction networks

How can understanding YciB function contribute to developing novel antimicrobial strategies?

YciB's role in maintaining cell envelope integrity presents promising avenues for antimicrobial development:

• Targeting YciB directly:

  • Design inhibitors that disrupt YciB function based on structural information

  • Target YciB-interacting proteins involved in cell division and elongation

  • Develop peptides that mimic interaction interfaces to disrupt protein-protein interactions

• Exploiting synthetic lethality:

  • Design compounds that inhibit DcrB function, which would be selectively toxic to bacteria with compromised YciB function

  • Identify additional synthetic lethal relationships with yciB that could be targeted

• Membrane homeostasis disruption:

  • Develop agents that alter membrane fluidity in ways that are particularly detrimental to bacteria lacking functional YciB

  • Target lipoprotein maturation pathways in conjunction with envelope stressors

• Vaccine development approaches:

  • Assess whether YciB epitopes could serve as vaccine candidates

  • Determine if YciB-deficient strains could serve as attenuated live vaccine candidates

What experimental systems best model the role of YciB in bacterial persistence?

To effectively study YciB's role in bacterial persistence, researchers should consider:

• Environmental persistence models:

  • Low-moisture food matrices to mimic dry food production environments where Salmonella Agona has shown remarkable persistence

  • Temperature fluctuation chambers to assess adaptation to changing environmental conditions

  • Biofilm formation assays on relevant surfaces (stainless steel, plastic)

• Genetic approaches:

  • Construction of reporter strains with fluorescent proteins under control of yciB promoter to monitor expression under different stress conditions

  • Creation of conditional mutants to study essential functions

  • CRISPR interference systems for tunable repression of yciB expression

• Host interaction models:

  • Macrophage survival assays to evaluate persistence within phagocytic cells

  • Gallstone biofilm models to study chronic infection

  • Animal models of chronic Salmonella infection

• Multi-omics integration:

  • Transcriptomic profiling of yciB mutants under various stress conditions

  • Proteomic analysis focusing on envelope proteins

  • Metabolomic assessment of lipid composition changes

How might YciB function relate to bacterial adaptation to environmental stresses?

YciB appears to play a critical role in bacterial adaptation to environmental stresses through its impact on envelope integrity:

• Osmotic stress adaptation:

  • YciB deletion mutants show increased susceptibility to low osmolarity

  • This suggests YciB may be important for maintaining cell envelope integrity during osmotic fluctuations

• Temperature adaptation:

  • The relationship between YciB and DcrB becomes particularly important at low temperatures

  • This indicates a role in maintaining membrane function during temperature shifts

• Persistence mechanisms:

  • The ability of Salmonella Agona to persist in food production environments for extended periods (10+ years) suggests sophisticated adaptation mechanisms

  • YciB may contribute to this persistence by helping maintain envelope integrity under adverse conditions

• Research approach recommendations:

  • Examine yciB expression patterns under various stress conditions

  • Test survival of yciB mutants after exposure to desiccation, temperature fluctuations, and nutrient limitation

  • Analyze membrane lipid composition changes in response to stress in wild-type versus yciB mutant strains