Recombinant Cronobacter sakazakii Bifunctional protein aas (aas)

What is the biochemical function of the Aas protein in Cronobacter sakazakii?

The Aas protein in C. sakazakii functions as a bifunctional enzyme with dual activities: 2-acylglycerophosphoethanolamine acyltransferase and acyl-ACP synthetase. While not explicitly detailed in the search results, this bifunctional protein likely plays roles in:

• Phospholipid remodeling through the transfer of acyl groups

• Fatty acid activation via the synthetase function

This protein may contribute to membrane maintenance and adaptation to environmental stresses, which is particularly relevant given C. sakazakii's ability to persist in various environments, including low-moisture conditions that make it problematic in powdered infant formula .

How does Aas protein expression relate to C. sakazakii virulence?

While the Aas protein is not specifically identified among the confirmed virulence factors in the search results, C. sakazakii pathogenicity involves multiple factors. Recent research has identified several virulence-associated proteins in C. sakazakii, including FabH, GshA, GppA, GcvH, IhfB, RfaC, and MsyB . The Aas protein may interact with these pathways, particularly since it likely functions in lipid metabolism, which can affect bacterial membrane integrity and adaptation to host environments.

Research indicates that the regulatory genes rcsA and treR influence C. sakazakii toxicity in zebrafish and rat models . Understanding how Aas expression is regulated, possibly by these or other transcriptional regulators, would provide insights into its potential role in virulence.

What are the optimal conditions for expressing recombinant C. sakazakii Aas protein?

For optimal expression of recombinant C. sakazakii Aas protein:

• Expression System: E. coli is the recommended host for expression

• Tags: N-terminal His-tag facilitates purification

• Construct Design: Full-length protein (1-719 amino acids) should be expressed for complete functionality

While specific expression conditions are not detailed in the search results, standard E. coli expression protocols would typically involve:

• Induction with IPTG (0.1-1.0 mM)

• Temperature optimization (often 16-37°C depending on protein solubility)

• Growth in rich media (such as LB or TB)

• Expression time optimization (4-24 hours)

What purification methods are most effective for isolating high-quality Aas protein?

Based on the His-tagged nature of the recombinant protein, a multi-step purification protocol is recommended:

• Initial Capture: Immobilized metal affinity chromatography (IMAC) using Ni-NTA or similar resin to capture the His-tagged protein

• Intermediate Purification: Size exclusion chromatography to separate the protein from aggregates and impurities

• Quality Assessment: SDS-PAGE to confirm purity (>90% purity is achievable)

The purified protein is typically supplied as a lyophilized powder for stability .

How should researchers properly reconstitute and store recombinant Aas protein?

For optimal handling and storage of recombinant Aas protein:

Reconstitution Protocol:

• Centrifuge the vial briefly to collect contents

• Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 5-50% (recommended 50%) for long-term storage

Storage Conditions:

• Store at -20°C/-80°C upon receipt

• Prepare working aliquots to avoid repeated freeze-thaw cycles

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

• Long-term storage requires -20°C/-80°C with glycerol as a cryoprotectant

The protein is provided in a Tris/PBS-based buffer containing 6% Trehalose at pH 8.0 .

What assays can be used to measure the enzymatic activity of Aas protein?

For assessing the dual enzymatic activities of the Aas protein:

Acyltransferase Activity Assay:

• Substrate preparation: 2-acylglycerophosphoethanolamine and acyl-CoA donors

• Reaction monitoring: HPLC or LC-MS to track substrate conversion and product formation

• Spectrophotometric assays: Coupling release of CoA with chromogenic reagents

Acyl-ACP Synthetase Activity Assay:

• Substrate preparation: Free fatty acids, ATP, and ACP

• Monitoring ATP consumption: Luciferase-based ATP detection

• Product detection: Native PAGE to visualize acylated ACP species

While the specific enzymatic parameters for the C. sakazakii Aas protein are not provided in the search results, these methodological approaches are consistent with standard biochemical characterization techniques for similar bifunctional enzymes.

How can researchers establish structure-function relationships for the Aas protein?

To establish structure-function relationships:

• Domain Mapping: Bioinformatic analysis to identify conserved domains for each function

• Site-Directed Mutagenesis: Create targeted mutations in predicted catalytic residues

• Truncation Analysis: Generate domain-specific constructs to isolate individual functions

• Crystal Structure Determination: X-ray crystallography or cryo-EM to resolve 3D structure

• Molecular Dynamics Simulations: Computational analysis of protein dynamics

These approaches would help delineate which regions of the 719-amino acid protein are responsible for the acyltransferase versus synthetase activities and identify critical residues for catalysis.

How does Aas protein expression relate to C. sakazakii persistence in environmental conditions?

C. sakazakii is known for its ability to persist in low-moisture environments, contributing to its presence in powdered infant formula . While specific data on Aas protein's role is not detailed in the search results, researchers investigating this relationship should consider:

• Desiccation Tolerance Assays: Compare survival rates between wild-type and Aas-knockout strains under low-moisture conditions

• Membrane Composition Analysis: Investigate changes in phospholipid profiles in response to environmental stresses

• Gene Expression Studies: Measure aas gene expression under various environmental conditions using RT-qPCR

• Comparative Genomics: Analyze aas gene conservation across C. sakazakii strains with variable environmental persistence

Recent research on RecA deletion has shown impacts on desiccation tolerance and environmental resilience in C. sakazakii . Similar methodologies could be applied to investigate the Aas protein's role.

What methods are most effective for studying Aas protein's role in virulence using animal models?

Based on successful C. sakazakii virulence studies, researchers should consider:

Animal Models:

• Zebrafish Model: Useful for high-throughput initial screening of virulence factors

• Rat Model: Provides more translational relevance to human infections

Experimental Approaches:

• Gene Knockout Studies: Generate Aas-deficient mutants and complemented strains

• Survival Analysis: Monitor host survival rates after infection with wild-type versus mutant strains

• Bacterial Load Quantification: Measure bacterial counts in blood and tissues

• Histopathological Examination: Assess tissue damage and inflammatory responses

• Transcriptomic Analysis: Identify genes co-regulated with aas during infection

Recent studies have successfully used such approaches to identify virulence factors in C. sakazakii, including the demonstration of reduced virulence in RecA knockout mutants .

How can protein-protein interaction studies help understand Aas protein's role in bacterial physiology?

To investigate the interaction network of Aas protein:

• Co-Immunoprecipitation: Using anti-His antibodies to pull down the His-tagged Aas protein and identify interacting partners

• Bacterial Two-Hybrid Assays: Screening for potential protein partners

• Cross-Linking Mass Spectrometry: Identifying spatial relationships between Aas and other proteins

• Proximity-Dependent Biotin Identification (BioID): Mapping the proximal protein environment

These methodologies could reveal interactions with known virulence factors identified in C. sakazakii, such as FabH, GshA, or regulatory proteins like RcsA and TreR , providing insights into how Aas contributes to bacterial physiology and pathogenicity.

What approaches can be used to develop inhibitors targeting the Aas protein as potential antimicrobials?

For inhibitor development targeting Aas protein:

• High-Throughput Screening:

  • Enzymatic activity-based assays to screen compound libraries

  • Fragment-based screening to identify initial chemical scaffolds

• Structure-Based Drug Design:

  • In silico docking studies using homology models or resolved structures

  • Rational design targeting catalytic sites of either enzymatic function

• Evaluation in Bacterial Systems:

  • Growth inhibition assays with identified compounds

  • Membrane integrity assessments

  • Synergy testing with existing antibiotics

• Validation in Animal Models:

  • Efficacy testing in zebrafish and rat models of C. sakazakii infection

  • Toxicity and pharmacokinetic assessments

Recent research identifying RecA as a promising target for mitigating C. sakazakii infections demonstrates the potential of targeting specific proteins to reduce pathogen virulence and environmental persistence .

How can researchers differentiate the dual functionalities of Aas protein in experimental settings?

To experimentally distinguish between the acyltransferase and synthetase activities:

• Selective Substrate Utilization:

  • Design assays with specific substrates for each function

  • Monitor reaction progress using mass spectrometry or chromatographic methods

• Domain-Specific Inhibitors:

  • Develop compounds targeting each functional domain separately

  • Use competitive inhibitors specific to each reaction type

• Mutational Analysis:

  • Create targeted mutations affecting each activity independently

  • Measure the impact on each function using biochemical assays

• Isotope Labeling Studies:

  • Track substrate utilization with isotope-labeled precursors

  • Use NMR or mass spectrometry to follow metabolic flux

This methodological approach would provide insights into whether the dual functions operate independently or exhibit regulatory cross-talk, and how each function contributes to bacterial physiology and virulence.