Recombinant Cronobacter sakazakii UPF0756 membrane protein ESA_02180 (ESA_02180)

What is Cronobacter sakazakii and why is ESA_02180 significant for research?

Cronobacter sakazakii (formerly known as Enterobacter sakazakii) is a gram-negative, rod-shaped, motile, non-spore forming bacterium that can cause serious infections in humans. This pathogen is particularly concerning because it can lead to neonatal meningitis, septicemia, and necrotizing enterocolitis in infants with mortality rates of 40-80% . The bacterium was first documented in 1961 when it was isolated from infants who died from meningitis .

ESA_02180 is a UPF0756 membrane protein found in C. sakazakii strain ATCC BAA-894. Its significance for research lies in understanding membrane proteins' roles in bacterial pathogenesis, particularly how these proteins might contribute to virulence, antibiotic resistance, and biofilm formation in C. sakazakii. While not extensively characterized, the protein may play roles in membrane integrity, transport, or signaling pathways that contribute to the bacterium's ability to cause disease.

What expression systems are suitable for producing recombinant ESA_02180 protein?

Several expression systems can be used for producing recombinant ESA_02180 protein, with different advantages depending on research needs:

For ESA_02180, E. coli expression systems offer the best yields and shorter turnaround times . In reported protocols, the protein has been successfully expressed with N-terminal His-tags in E. coli, facilitating purification via affinity chromatography . Recombinant proteins can be stored in Tris-based buffer with 50% glycerol at -20°C or -80°C for extended storage .

What are the standard methods for purification of recombinant ESA_02180?

Standard purification methods for recombinant ESA_02180 involve:

• Expression in E. coli with an N-terminal His-tag

• Cell harvesting by centrifugation

• Cell lysis via sonication or high-pressure homogenization

• Affinity chromatography using Ni-NTA or similar matrices

• Elution with imidazole

• Buffer exchange and concentration

• Additional polishing steps (optional): size exclusion chromatography or ion exchange chromatography

For membrane proteins like ESA_02180, detergent-based extraction may be necessary to solubilize the protein from the membrane fraction. After purification, the protein is typically stored in a stabilizing buffer containing glycerol to prevent aggregation and maintain activity during freezing and thawing. Reports indicate that repeated freeze-thaw cycles should be avoided, and working aliquots should be stored at 4°C for up to one week .

How does ESA_02180 potentially contribute to Cronobacter sakazakii pathogenicity and virulence?

While the specific function of ESA_02180 in pathogenicity is not well characterized in the provided literature, we can draw insights from studies on related membrane proteins in C. sakazakii and similar bacteria:

• Membrane integrity and permeability: As a membrane protein, ESA_02180 may influence the structural integrity of the bacterial cell envelope, affecting permeability to antimicrobial compounds.

• Adhesion and invasion mechanisms: Other membrane proteins in C. sakazakii, such as OmpA and OmpX, have been shown to play roles in adherence to and invasion of human cell lines . Studies have demonstrated that C. sakazakii strains can adhere to and invade human epithelial (HEp-2) cells, with adherence mean values of approximately 22 × 10^4 CFU/mL and invasion rates around 3.3% .

• Biofilm formation: Recent research has identified relationships between membrane proteins, biofilm formation, and virulence in C. sakazakii . For example, the lysozyme inhibitor LprI (modulated by HmsP and c-di-GMP) has been shown to be a key factor in biofilm formation and virulence.

• Antibiotic resistance: Membrane proteins can contribute to antibiotic resistance. Studies show that 83% of C. sakazakii strains isolated from powdered infant formula were resistant to multiple antibiotics, with 80% resistant to cephalothin .

Further research using gene knockout or protein interaction studies would be necessary to definitively establish ESA_02180's role in virulence.

What techniques are most effective for studying the structure-function relationship of ESA_02180?

Several advanced techniques can be employed to study the structure-function relationship of ESA_02180:

• Structural determination:

  • X-ray crystallography (challenging for membrane proteins)

  • Cryo-electron microscopy

  • Nuclear magnetic resonance (NMR) spectroscopy for specific domains

  • Computational modeling and molecular dynamics simulations

• Functional analysis:

  • Site-directed mutagenesis to identify critical residues

  • Gene knockout/knockdown studies in C. sakazakii

  • Protein-protein interaction studies (pull-downs, yeast two-hybrid)

  • Lipid binding assays

• Cellular localization:

  • Immunofluorescence microscopy with tagged proteins

  • Subcellular fractionation

  • Protease accessibility assays

• Physiological relevance:

  • Virulence assays in cell culture models

  • Biofilm formation assays

  • Antibiotic susceptibility testing

A comprehensive approach would combine structural insights with functional data to elucidate how ESA_02180's structure relates to its biological function in C. sakazakii.

How can researchers design experiments to evaluate the immunogenicity of ESA_02180?

To evaluate the immunogenicity of ESA_02180, researchers can design experiments similar to those used for other C. sakazakii proteins like GroEL and OmpX :

• Animal immunization studies:

  • Express and purify recombinant ESA_02180

  • Immunize animal models (mice, rats) with purified protein

  • Collect serum at different time points post-immunization

  • Measure antibody titers using ELISA or other immunoassays

  • Assess protective efficacy through bacterial challenge experiments

• Epitope mapping:

  • Use bioinformatics to predict potential B-cell and T-cell epitopes

  • Synthesize peptide arrays covering the protein sequence

  • Test reactivity with serum from immunized animals or infected individuals

  • Identify immunodominant regions of the protein

• Maternal immunity studies:

  • Immunize pregnant animals with recombinant ESA_02180

  • Challenge offspring with C. sakazakii

  • Evaluate protection against infection

For example, in a study with other C. sakazakii proteins, researchers immunized pregnant rats with recombinant proteins, then challenged 3-day-old offspring with 1 × 10^6 CFU/rat of C. sakazakii. Brain and blood samples were collected to analyze bacterial infection and determine protective efficacy .

What are the methodological challenges in studying membrane proteins like ESA_02180 and how can they be addressed?

Studying membrane proteins like ESA_02180 presents several methodological challenges:

For ESA_02180 specifically, researchers should optimize expression conditions in E. coli (temperature, inducer concentration, duration), screen multiple detergents for solubilization, and use stabilizing additives in buffers. If the protein forms inclusion bodies, refolding protocols using mild detergents can be employed .

How does ESA_02180 compare to other membrane proteins in Cronobacter sakazakii, and what can we learn from comparative analyses?

Comparative analysis of ESA_02180 with other C. sakazakii membrane proteins can provide insights into its potential functions:

• Sequence and structural homology:

  • Comparing ESA_02180 with well-characterized membrane proteins like OmpA and OmpX, which are involved in adhesion and invasion of host cells

  • Identifying conserved domains or motifs that might suggest functional roles

• Evolutionary conservation:

  • Analyzing the presence of ESA_02180 homologs across different Cronobacter species and related Enterobacteriaceae

  • Evaluating sequence conservation in pathogenic versus non-pathogenic strains

• Expression patterns:

  • Comparing expression levels of ESA_02180 under different growth conditions (temperature, pH, nutrient availability)

  • Determining if ESA_02180 is differentially expressed during host cell interaction or biofilm formation

• Functional redundancy:

  • Investigating whether other proteins can compensate for ESA_02180 loss in knockout studies

  • Identifying potential interaction partners within the membrane protein network

Experimental approaches might include comparative proteomics, transcriptomics under various conditions, and systematic functional analysis of multiple membrane proteins to build a comprehensive understanding of their roles in C. sakazakii biology and pathogenesis.

What role might ESA_02180 play in biofilm formation and how can this be experimentally validated?

Biofilm formation is a critical virulence factor for C. sakazakii, enabling persistence in hostile environments and resistance to antimicrobial agents. While the specific role of ESA_02180 in biofilm formation is not established in the provided literature, several experimental approaches can be used to investigate this potential function:

• Gene knockout studies:

  • Create an ESA_02180 deletion mutant in C. sakazakii

  • Compare biofilm formation between wild-type and mutant strains using crystal violet staining, confocal microscopy, or other quantitative methods

  • Perform complementation studies to confirm phenotype is due to the specific gene deletion

• Expression analysis:

  • Measure ESA_02180 expression levels during different stages of biofilm formation using qRT-PCR or RNA-seq

  • Compare expression in planktonic versus biofilm cells

• Protein localization in biofilms:

  • Use fluorescently tagged ESA_02180 to visualize its distribution within biofilm structures

  • Perform immunogold labeling with anti-ESA_02180 antibodies for electron microscopy

• Interaction studies:

  • Identify potential interactions between ESA_02180 and extracellular DNA, proteins, or polysaccharides in the biofilm matrix

  • Investigate interactions with known biofilm regulators like HmsP or c-di-GMP signaling components

Recent research has shown that another C. sakazakii protein, the lysozyme inhibitor LprI, plays a significant role in biofilm formation and binds extracellular DNA, anchoring bacteria within the biofilm matrix . Similar mechanisms could be investigated for ESA_02180.

How might ESA_02180 be utilized in developing diagnostic tools for Cronobacter sakazakii detection?

ESA_02180 could potentially serve as a target for developing sensitive and specific diagnostic tools for C. sakazakii detection, particularly in food safety applications:

• Antibody-based detection methods:

  • Develop monoclonal or polyclonal antibodies against recombinant ESA_02180

  • Create immunoassays (ELISA, lateral flow) for rapid detection in food samples

  • Implement immunomagnetic separation techniques for bacterial concentration

• Nucleic acid-based detection:

  • Design PCR primers targeting the ESA_02180 gene

  • Develop multiplex PCR or real-time PCR assays for concurrent detection of multiple targets

  • Create DNA microarrays incorporating ESA_02180 with other virulence genes

• Aptamer-based biosensors:

  • Select DNA/RNA aptamers with high affinity for ESA_02180

  • Develop electrochemical or optical biosensors for sensitive detection

• Mass spectrometry-based approaches:

  • Identify unique peptide signatures of ESA_02180 for MALDI-TOF MS identification

  • Develop targeted proteomics assays for detection in complex samples

The development of such tools is particularly important given the severity of C. sakazakii infections in infants and the association with contaminated powdered infant formula. Current diagnostic methods can detect C. sakazakii nucleic acid using PCR targeting the bacterial outer membrane protein A (ompA) gene , and similar approaches could be developed for ESA_02180.

What experimental approaches can be used to determine if ESA_02180 is a potential target for antimicrobial development?

To evaluate ESA_02180 as a potential antimicrobial target, researchers can employ several experimental approaches:

• Essentiality studies:

  • Create conditional knockouts or use CRISPR interference to modulate ESA_02180 expression

  • Determine if the protein is essential for bacterial growth or virulence

  • Assess growth kinetics and morphological changes in depletion strains

• Target validation:

  • Perform in silico drug binding site analysis

  • Conduct high-throughput screening of compound libraries against the recombinant protein

  • Validate hits using biophysical methods (thermal shift assays, surface plasmon resonance)

• Functional inhibition studies:

  • Design peptide inhibitors based on structure predictions

  • Test antibodies or nanobodies for functional blocking activity

  • Evaluate natural products for specific inhibition

• In vitro and in vivo efficacy:

  • Test candidate inhibitors for growth inhibition or biofilm disruption

  • Evaluate cytotoxicity in mammalian cell lines

  • Assess efficacy in relevant animal infection models

• Resistance development:

  • Study potential resistance mechanisms through laboratory evolution

  • Analyze clinical isolates for natural variations in ESA_02180 sequence or expression

The growing concern over antibiotic resistance in C. sakazakii makes this research direction particularly important. Studies have shown that 83% of C. sakazakii strains isolated from powdered infant formula were resistant to 1-7 antibiotics, with resistance to cephalothin being particularly common (80%) .

How can researchers investigate the potential role of ESA_02180 in Cronobacter sakazakii adaptation to different environments?

C. sakazakii can survive in diverse environments, including dry foods like powdered infant formula and various hospital settings. To investigate ESA_02180's potential role in environmental adaptation:

• Stress response studies:

  • Monitor ESA_02180 expression under various stress conditions (desiccation, osmotic stress, pH shifts, heat shock)

  • Compare survival rates between wild-type and ESA_02180 mutant strains under stress conditions

  • Assess membrane integrity changes during stress response

• Desiccation resistance:

  • Evaluate the survival of ESA_02180 mutants during drying and rehydration cycles

  • Compare fatty acid composition and membrane fluidity in wild-type versus mutant strains

  • Assess recovery rates after extended periods in low-moisture environments

• Biofilm formation in different media:

  • Analyze biofilm architecture and composition in food-related versus clinical environments

  • Determine if ESA_02180 expression or localization changes in biofilms formed on different surfaces

• Host adaptation:

  • Study ESA_02180 expression during interaction with different host cell types

  • Compare invasion efficiency in epithelial versus immune cells

  • Assess protein modification or regulation during host-pathogen interaction

Understanding how membrane proteins like ESA_02180 contribute to environmental adaptation could help develop strategies to control C. sakazakii in food production environments and prevent contamination of infant formula.

What approaches can be used to study potential interactions between ESA_02180 and host immune system components?

Understanding interactions between bacterial proteins and host immunity is crucial for developing effective vaccines and therapeutics. For ESA_02180, several approaches can be employed:

• Immune recognition studies:

  • Test recognition of purified ESA_02180 by pattern recognition receptors (TLRs, NODs)

  • Measure cytokine production by immune cells exposed to the protein

  • Determine if ESA_02180 activates or suppresses immune signaling pathways

• Antibody-mediated immunity:

  • Evaluate antibody responses to ESA_02180 in animal models

  • Test whether anti-ESA_02180 antibodies can neutralize bacterial attachment or invasion

  • Assess if passive immunization with these antibodies provides protection

• Cellular immunity:

  • Characterize T-cell responses to ESA_02180 epitopes

  • Measure T-cell proliferation and cytokine production

  • Identify potential MHC-presented peptides from ESA_02180

• Maternal immunity transfer:

  • Study placental transfer of anti-ESA_02180 antibodies in animal models

  • Evaluate protection of neonates through maternal immunization

  • Compare with other immunogenic C. sakazakii proteins like GroEL and OmpX

Previous research has demonstrated that immunization with certain C. sakazakii proteins can induce protective immune responses. For instance, immunization of pregnant rats with recombinant GroEL and OmpX resulted in protective effects in their offspring when challenged with C. sakazakii .

What are the latest methodological advances in studying membrane proteins that could be applied to ESA_02180 research?

Recent technological advances have expanded our ability to study challenging membrane proteins like ESA_02180:

• Structural biology innovations:

  • Cryo-electron microscopy advances enabling atomic-resolution structures of membrane proteins without crystallization

  • Integrative structural biology combining multiple techniques (NMR, SAXS, crosslinking mass spectrometry)

  • Computational methods like AlphaFold2 for structure prediction

• Membrane mimetics:

  • Nanodiscs composed of membrane scaffold proteins and phospholipids

  • Styrene-maleic acid lipid particles (SMALPs) for native membrane protein extraction

  • Cell-free expression systems with direct incorporation into liposomes

• Single-molecule techniques:

  • Single-molecule FRET to study conformational changes

  • Atomic force microscopy for topographical and mechanical properties

  • Optical tweezers for measuring forces in membrane protein dynamics

• In-cell structural biology:

  • In-cell NMR to study membrane proteins in their native environment

  • Proximity labeling methods (BioID, APEX) to identify interaction partners

  • Super-resolution microscopy for visualizing membrane protein organization

• High-throughput functional screening:

  • CRISPR-based screening for functional characterization

  • Microfluidic platforms for rapid protein engineering and activity testing

  • Automated patch clamp systems for electrophysiological characterization

Applying these cutting-edge methods to ESA_02180 could provide unprecedented insights into its structure, function, and role in C. sakazakii pathogenesis.

How does research on ESA_02180 fit into the broader context of Cronobacter sakazakii pathogenesis studies?

Research on ESA_02180 should be integrated into the broader understanding of C. sakazakii pathogenesis, which encompasses several key areas:

• Virulence mechanisms: Studies have identified various virulence factors in C. sakazakii, including outer membrane proteins that promote adhesion and invasion. For example, OmpA and OmpX have been implicated in basolateral invasion of human enterocyte-like Caco-2 and intestinal epithelial cells . Understanding how ESA_02180 might interact with or complement these known virulence factors is important.

• Antibiotic resistance: 83% of C. sakazakii strains isolated from powdered infant formula were resistant to 1-7 antibiotics . If ESA_02180 contributes to membrane permeability or efflux pump function, it could influence antibiotic susceptibility.

• Biofilm formation: Recent research has identified the role of proteins like lysozyme inhibitor LprI in biofilm formation and virulence . Investigating whether ESA_02180 participates in biofilm formation pathways would be valuable.

• Host-pathogen interactions: C. sakazakii can adhere to and invade human epithelial cells with adherence mean values of approximately 22 × 10^4 CFU/mL and invasion rates around 3.3% . The role of ESA_02180 in these processes deserves investigation.

• Environmental persistence: C. sakazakii can survive in dry foods and has been found in powdered infant formula with contamination levels of 0.22–1.61 MPN/100g . Membrane proteins may contribute to desiccation resistance.

Integrating ESA_02180 research into these broader contexts will provide a more comprehensive understanding of C. sakazakii pathogenesis.

What bioinformatic approaches can be used to predict potential functions of ESA_02180 based on sequence and structural features?

Several bioinformatic approaches can help predict potential functions of ESA_02180:

• Sequence-based analyses:

  • Homology searches using BLAST, HMMer against protein databases

  • Identification of conserved domains using Pfam, InterPro, or CDD

  • Sequence motif discovery for functional site prediction

  • Transmembrane topology prediction using TMHMM or Phobius

• Structural prediction and analysis:

  • 3D structure prediction using AlphaFold2 or RoseTTAFold

  • Molecular dynamics simulations to study conformational dynamics

  • Binding site prediction using computational algorithms

  • Electrostatic surface analysis for potential interaction sites

• Evolutionary analyses:

  • Phylogenetic profiling to identify co-evolving proteins

  • Analysis of selection pressure to identify functionally important residues

  • Comparison with homologs in other bacterial species

• Functional network inference:

  • Protein-protein interaction prediction based on co-expression data

  • Genomic context analysis (operons, gene neighborhoods)

  • Integration of multi-omics data to predict functional relationships

• Pathway analysis:

  • Mapping potential functions to known bacterial pathways

  • Identifying potential roles in transport, signaling, or metabolism