Recombinant Salmonella dublin Protein CrcB homolog (crcB)
Description
General Information on CrcB Homologs
CrcB homologs are found in various bacteria and are often involved in carbon catabolite repression, a regulatory mechanism that prioritizes the use of preferred carbon sources over others . Although the precise function of CrcB in S. dublin may differ in some aspects from other bacteria, the core function is likely related to regulatory control.
Role in Virulence and Infection
Small proteins like MgrB have a role in Salmonella virulence . MgrB regulates the activity of the PhoPQ TCS, which is conserved in E. coli . A study showed that Δ mgrB Salmonella is impaired at all stages of macrophages and epithelial cells infection, relative to the isogenic wild-type strain . MgrB has a positive effect on flagella and motility-related genes at both the transcript and protein level and is linked to PhoPQ .
Regulatory Mechanisms Involving CrcB Homologs
The RcsCDB phosphorelay system controls a large regulon in Enterobacteriaceae, impacting biofilm formation, flagella production, synthesis of extracellular capsules, and cell division . The final effector of the RcsCDB system is the response regulator RcsB, which activates or represses multiple genes by binding to different promoter regions . RcsB can act alone or with other transcriptional factors, with its phosphorylation state influencing its activity .
Interactions with Other Proteins
RcsB interacts with proteins such as GadE, BglJ, MatA, or RflM . The auxiliary proteins TviA and RmpA have also been proposed to act in concert with RcsB .
Examples of Experimental Findings
Product Specs
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Target Background
Crucial in reducing intracellular fluoride concentration, thereby mitigating its toxicity.
KEGG: sed:SeD_A0731
Q&A
What is Recombinant Salmonella dublin Protein CrcB homolog (crcB)?
Recombinant Salmonella dublin Protein CrcB homolog (crcB) is a full-length protein (127 amino acids) derived from Salmonella dublin bacteria. It is classified as a putative fluoride ion transporter, with UniProt ID B5FMM5 . This protein is typically produced through recombinant expression in E. coli systems, often with an N-terminal His tag to facilitate purification and downstream experimental applications. The protein exists naturally in Salmonella dublin, a host-adapted serovar that has gained attention due to its increasing prevalence in dairy operations and its multidrug-resistant characteristics .
How should Recombinant Salmonella dublin Protein CrcB be stored for research purposes?
For optimal stability and activity retention, the following storage protocols are recommended:
| Storage Condition | Recommendation | Purpose |
|---|---|---|
| Short-term storage | 4°C for up to one week | Working aliquots |
| Long-term storage | -20°C/-80°C | Extended preservation |
| Storage buffer | Tris-based buffer with 50% glycerol, pH 8.0 | Stability enhancement |
| Important precautions | Avoid repeated freeze-thaw cycles | Prevent protein degradation |
The recommended reconstitution procedure involves:
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Brief centrifugation of the vial before opening
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Reconstitution in deionized sterile water to a concentration of 0.1-1.0 mg/mL
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Addition of glycerol to a final concentration of 5-50% for long-term storage
What is the role of CrcB in Salmonella pathogenicity and virulence?
While the specific role of CrcB in Salmonella dublin virulence isn't directly established in the provided literature, its function should be considered within the broader context of Salmonella dublin's virulence mechanisms. Salmonella dublin expresses numerous virulence factors that contribute to its invasive capacity, including:
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Type III Secretion Systems encoded by Salmonella Pathogenicity Islands (SPI-1 and SPI-2), which facilitate intestinal invasion and systemic spread
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Type VI Secretion Systems from SPI-6 and SPI-19, which enable injection of effector proteins into host cells
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The pSDV plasmid with spv operon associated with host cellular apoptosis
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Flagella encoded by the gene fliC that enable motility and chemotaxis responses
As a putative fluoride ion transporter, CrcB may contribute to ion homeostasis and potentially play a role in environmental adaptation during infection processes. Research into its specific contribution to virulence would require gene knockout studies and subsequent virulence assessment in appropriate model systems.
How does CrcB contribute to antimicrobial resistance in Salmonella dublin?
The relationship between CrcB and antimicrobial resistance in Salmonella dublin represents an important research frontier. Salmonella dublin has emerged as one of the most multidrug-resistant serotypes in the United States, with resistance documented against multiple antimicrobial classes .
Antimicrobial resistance in Salmonella develops through different mechanisms depending on the drug:
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Fluoroquinolone resistance typically occurs through chromosomal mutations and clonal dissemination
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Cephalosporin resistance usually develops through acquisition of mobile genetic elements via plasmids and transposons
The National Antimicrobial Resistance Monitoring System (NARMS) reported that among S. Dublin isolates:
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84% were resistant to five or more classes of antimicrobial drugs
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57% were resistant to seven or more antimicrobial classes
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There was an increase from 29% to 79% in isolates resistant to one or more antimicrobial classes when comparing 1996-2004 with 2005-2013
Studies have documented S. Dublin resistance to multiple antibiotics including:
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Ampicillin
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Chloramphenicol
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Neomycin
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Tetracycline
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Streptomycin
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Sulfonamide
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Amoxicillin/clavulanic acid
While the direct contribution of CrcB to this resistance profile has not been specifically delineated in the provided sources, its potential role in ion transport could influence bacterial membrane permeability and possibly affect drug uptake or efflux. Research investigating CrcB knockout strains and their antimicrobial susceptibility profiles would provide valuable insights into whether this protein contributes to the multidrug resistance phenotype.
What experimental approaches are recommended for studying CrcB function?
To systematically investigate CrcB function in Salmonella dublin, researchers should consider the following methodological approaches:
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Gene Expression Analysis
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qRT-PCR to quantify crcB expression under different environmental conditions
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RNA-seq to identify co-regulated genes in the CrcB regulon
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Reporter gene assays to monitor promoter activity
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Protein Localization and Interaction Studies
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Fluorescent protein tagging for subcellular localization
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Immunoprecipitation coupled with mass spectrometry to identify protein-protein interactions
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Bacterial two-hybrid systems to validate specific interactions
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Membrane fractionation to confirm membrane association
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Functional Characterization
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Gene deletion and complementation studies
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Site-directed mutagenesis of conserved residues
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Fluoride sensitivity assays (given its putative role as a fluoride transporter)
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Ion flux measurements using fluorescent indicators or radioisotopes
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Electrophysiological studies in reconstituted membrane systems
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Structural Analysis
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X-ray crystallography or cryo-EM for high-resolution structural determination
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Circular dichroism for secondary structure analysis
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Limited proteolysis to identify domain boundaries
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How does Salmonella dublin CrcB compare with homologs in other bacterial species?
Comparative analysis of CrcB homologs across bacterial species provides valuable evolutionary and functional insights. The CrcB protein belongs to a conserved family of membrane proteins found in many bacterial species, with primary function typically associated with fluoride ion transport.
Key comparative aspects include:
| Characteristic | Salmonella dublin CrcB | CrcB in Other Species |
|---|---|---|
| Sequence length | 127 amino acids | Typically 120-130 amino acids |
| Membrane topology | Multiple transmembrane domains | Generally conserved topology |
| Conservation | High sequence similarity within Enterobacteriaceae | Moderately conserved across bacterial phyla |
| Function | Putative fluoride ion transporter | Confirmed fluoride ion channel in some species |
| Association with virulence | Under investigation | Variable, species-dependent |
Homology modeling using better-characterized CrcB proteins as templates could provide structural insights into the Salmonella dublin protein. Additionally, complementation studies in heterologous systems could determine functional conservation across species.
What are the optimal conditions for recombinant expression and purification of CrcB?
Based on the available information, the following protocol represents current best practices for recombinant CrcB expression and purification:
Expression System:
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Host: E. coli (strain optimization may be required)
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Vector: Expression vector with N-terminal His-tag
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Induction: IPTG-inducible promoter system (optimization of concentration and temperature recommended)
Purification Protocol:
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Cell lysis via sonication or French press in appropriate buffer
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Membrane fraction isolation via ultracentrifugation
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Solubilization using mild detergents (e.g., DDM, LDAO)
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Immobilized metal affinity chromatography (IMAC) using Ni-NTA resin
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Size exclusion chromatography for further purification
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Final product stored in Tris-based buffer with 50% glycerol at pH 8.0
Protein Quality Assessment:
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Purity confirmation via SDS-PAGE (>90% purity is typically achieved)
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Western blot analysis with anti-His antibodies
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Activity assays (e.g., fluoride transport assays)
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Circular dichroism to confirm proper folding
How can CrcB be utilized in antimicrobial resistance research?
Given the increasing prevalence of multidrug-resistant Salmonella Dublin strains, CrcB represents a potential target for antimicrobial research strategies. Researchers could explore:
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CrcB as a Drug Target:
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Development of specific inhibitors targeting CrcB function
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Screening of compound libraries against purified CrcB
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Structure-based drug design once crystal structure is determined
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Role in Resistance Mechanisms:
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Investigation of CrcB expression levels in resistant vs. susceptible strains
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Analysis of genetic variations in crcB gene across resistant isolates
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Determination of whether CrcB influences uptake or efflux of antimicrobial compounds
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Combination Therapies:
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Assessment of synergistic effects between CrcB inhibitors and conventional antibiotics
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Evaluation of ion transport inhibitors as resistance modifiers
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The multi-drug resistance profile of Salmonella Dublin to critical antibiotics (including ampicillin, chloramphenicol, tetracycline, and ceftriaxone) makes this research particularly urgent from a public health perspective .
What methods are effective for studying CrcB's role in Salmonella Dublin virulence?
To elucidate CrcB's contribution to Salmonella Dublin's distinctive virulence profile, researchers should consider:
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Animal Models:
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Bovine infection models (given S. Dublin's host adaptation)
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Mouse models for preliminary screening
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Cell culture systems using bovine intestinal and macrophage cell lines
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Virulence Assays:
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Invasion assays in epithelial cell lines
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Intracellular survival in macrophages
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Biofilm formation assays
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Competitive index experiments with wildtype and crcB mutants
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Transcriptomic Approaches:
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RNA-seq analysis of host response to wildtype vs. crcB mutants
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Identification of virulence factors co-regulated with crcB
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Salmonella Dublin's clinical manifestation is more severe than other Salmonella serovars due to its enhanced invasive capacity in cattle . Understanding CrcB's contribution to this characteristic could provide valuable insights for intervention strategies.
What are common challenges in working with recombinant CrcB and how can they be addressed?
Researchers working with recombinant CrcB often encounter several technical challenges:
| Challenge | Potential Solution |
|---|---|
| Low expression levels | Optimize codon usage for expression host; test different promoter systems; evaluate different E. coli strains |
| Protein insolubility | Express as fusion protein with solubility enhancers; optimize lysis and extraction buffers; use mild detergents for membrane protein extraction |
| Protein instability | Add stabilizing agents to buffer; optimize pH and ionic strength; maintain consistent cold chain |
| Loss of activity during purification | Minimize purification steps; confirm activity at each purification stage; identify stabilizing conditions |
| Aggregation | Include low concentrations of appropriate detergents; optimize protein concentration; include reducing agents if appropriate |
When troubleshooting purification issues, researchers should consider implementing a systematic approach testing different buffer compositions, detergents, and stabilizing agents to identify optimal conditions for maintaining CrcB structural integrity and function.
How can researchers validate the functional activity of purified recombinant CrcB?
Functional validation of purified CrcB is essential before proceeding with downstream applications. Recommended validation approaches include:
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Transport Activity Assays:
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Fluoride ion transport assays using fluorescent indicators
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Liposome reconstitution assays to measure ion flux
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Patch-clamp electrophysiology on reconstituted channels
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Binding Assays:
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Fluoride binding assays using isothermal titration calorimetry
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Fluorescence-based ligand binding assays
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Surface plasmon resonance with potential interacting partners
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Structural Integrity Assessment:
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Circular dichroism to confirm secondary structure
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Size exclusion chromatography to verify oligomeric state
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Thermal shift assays to assess stability
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These complementary approaches provide a comprehensive assessment of CrcB functionality, ensuring that the recombinant protein maintains native-like properties suitable for further experimental applications.
