Recombinant Salmonella agona Bifunctional protein aas (aas)

What is the Bifunctional protein aas in Salmonella agona?

Bifunctional protein aas in Salmonella agona (strain SL483) is a multifunctional enzyme with 2-acylglycerophosphoethanolamine acyltransferase activity (EC 2.3.1.40). The protein contains 719 amino acids in its full-length form and has a molecular structure that enables its dual functionality. It plays crucial roles in phospholipid metabolism and membrane homeostasis in Salmonella. The protein has been assigned the UniProt ID B5F4V4 specifically for the S. agona strain SL483, which has been extensively studied due to its involvement in outbreaks .

How conserved is the aas gene across different Salmonella serovars?

The aas gene shows significant conservation across different Salmonella serovars, similar to other structural genes like FlgK which demonstrates >97% conservation among ten major Salmonella serovars including S. Arizonae, S. Typhimurium, S. Typhi, S. Paratyphi A, S. Choleraesuis, S. Enteriditis, S. Heidelberg, S. Schwarzengrund, S. Agona, and S. Paratyphi B . This high degree of conservation makes aas a potential candidate for cross-serovar studies and applications. Comparative genomic analyses of Salmonella isolates from different outbreaks and sources have revealed that such conserved genes maintain their sequence integrity even in isolates separated by significant time periods, as demonstrated in the 1998 and 2008 S. Agona outbreaks analyzed through whole genome sequencing .

What are the optimal conditions for expressing recombinant Salmonella agona aas protein?

The optimal expression of recombinant S. agona Bifunctional protein aas depends on the expression system chosen. Based on current research practices, the protein has been successfully expressed in both E. coli and yeast expression systems. For E. coli-based expression, the following protocol has shown efficacy:

• Cloning the aas gene into a vector containing an N-terminal His-tag

• Transformation into an E. coli expression strain (BL21 or equivalent)

• Induction with IPTG (0.1-1.0 mM) at mid-log phase (OD600 = 0.6-0.8)

• Growth at reduced temperature (16-25°C) for 16-18 hours to enhance soluble protein production

• Lysis using buffer containing appropriate protease inhibitors

For yeast-based expression systems, which have been used to produce partial aas protein with >85% purity (SDS-PAGE), different optimization parameters apply .

What purification strategies yield the highest purity of functional aas protein?

Purification of recombinant aas protein to high purity (>90% as determined by SDS-PAGE) typically involves a multi-step approach:

• Initial capture using immobilized metal affinity chromatography (IMAC) for His-tagged proteins

• Intermediate purification using ion exchange chromatography (IEX)

• Polishing step using size exclusion chromatography (SEC)

The buffer composition greatly influences protein stability and yield, with optimal results observed using Tris/PBS-based buffers with 6% Trehalose at pH 8.0 for final storage . The purified protein should be lyophilized or stored with 50% glycerol to maintain stability during long-term storage at -20°C/-80°C. Repeated freeze-thaw cycles should be avoided to prevent protein degradation and loss of activity .

What experimental approaches best determine the enzymatic activity of recombinant aas protein?

The enzymatic activity of recombinant Bifunctional protein aas can be characterized through several complementary approaches:

• 2-acylglycerophosphoethanolamine acyltransferase assay: This assay measures the transfer of acyl groups from acyl-ACP to 2-acyl-GPE using radiolabeled substrates or HPLC-based detection methods.

• Coupled enzyme assays: These assays link aas activity to the production of detectable products through secondary enzymatic reactions.

• Membrane integration studies: Since aas functions in membrane phospholipid metabolism, liposome-based assays can provide insights into its membrane activity.

Factors affecting enzymatic assays include pH (optimal range typically 7.0-8.0), temperature, divalent cation concentration (particularly Mg²⁺), and substrate specificity .

How do mutations in the aas gene affect protein function and bacterial physiology?

Mutations in the aas gene can significantly impact both protein function and bacterial physiology. Key observations from genomic studies include:

• Single amino acid substitutions can alter substrate specificity or catalytic efficiency

• Mutations in conserved domains may render the protein completely inactive

• Loss of aas function can lead to altered membrane phospholipid composition

In Salmonella, aas gene mutations have been shown to affect:

• Membrane permeability and fluidity

• Resistance to membrane-targeting antimicrobials

• Survival under phosphate-limited conditions

• Virulence and pathogenicity in infection models

Genomic analysis of Salmonella isolates has revealed that certain genes may undergo adaptive mutations during infection or environmental persistence, although specific data on aas mutations is limited compared to other genes like those involved in pathogenicity islands or antimicrobial resistance .

Is aas protein directly involved in antimicrobial resistance mechanisms in Salmonella agona?

While aas itself is not directly classified as an antimicrobial resistance gene, its role in membrane phospholipid metabolism indirectly contributes to membrane composition and integrity, which can affect susceptibility to membrane-targeting antimicrobials. Current evidence does not suggest that aas functions as a resistance determinant like the well-characterized mdsA and mdsB efflux pump genes .

• Plasmid-borne resistance genes (up to 16 different ARGs on a single plasmid)

• Chromosomal mutations in target genes

• Efflux pump systems (including mdsA and mdsB)

• Mobile genetic elements carrying resistance determinants

A multidrug-resistant S. Agona isolate characterized in 2018 carried 23 different antibiotic resistance genes conferring resistance to 12 different antibiotic classes, as well as genes for resistance to six different heavy metals . The largest plasmid in this isolate (pSE18-SA00377-1, 295,499 bp) belonged to the IncHI2 family and carried 16 antibiotic resistance genes organized in two distinct clusters .

How does recombinant aas protein expression correlate with antibiotic susceptibility profiles?

• Overexpression of membrane proteins like aas may alter membrane properties

• Changes in membrane phospholipid composition can affect permeability to antibiotics

• Expression levels of aas may be altered in response to certain antibiotic exposures

Research on S. Agona isolates from various sources has shown that antimicrobial resistance profiles vary considerably between isolates, with some carrying resistance to multiple antibiotic classes. Genomic analyses have revealed that resistance genes are often carried on plasmids or within mobile genetic elements rather than being chromosomally encoded like aas .

What epitope mapping techniques are most effective for identifying antigenic regions in aas protein?

Epitope mapping of Salmonella proteins can be accomplished through both computational prediction and experimental validation approaches. Based on methodologies applied to other Salmonella proteins like FlgK, effective techniques include:

• Computational prediction:

  • VaxiJen (v2.0) for antigenicity prediction with threshold set at 0.4

  • AllerTOP (v2.0) using auto cross covariance for allergenicity assessment

  • ToxinPred for toxicity analysis

  • Protein-Sol server for physiological properties prediction

  • Vaxign2 for adhesion prediction

• Experimental validation:

  • Immunoprecipitation combined with mass spectrometry

  • Peptide arrays

  • Expression of protein fragments and immunoblotting

  • X-ray crystallography of antibody-antigen complexes

The combination of in silico prediction and in vivo experimental validation has successfully identified consensus peptide epitope sequences in other Salmonella proteins. Similar approaches could be applied to map epitopes in the aas protein for potential diagnostic or vaccine applications .

How can whole genome sequencing enhance understanding of aas gene evolution in different Salmonella agona lineages?

Whole genome sequencing (WGS) provides powerful insights into the evolution of genes like aas across different Salmonella lineages. In a study of S. Agona isolates from two outbreaks separated by ten years (1998 and 2008), WGS revealed:

• Only a mean of eight SNP differences between isolates from both outbreaks

• Evidence that the 2008 outbreak involved direct descendants of the 1998 outbreak strain

• Persistence of Salmonella in food processing facilities over extended periods

For aas gene evolution studies, WGS approaches should include:

• Comparative genomics to identify SNPs and structural variations in the aas gene

• Pan-genome analysis to determine if aas is part of the core or accessory genome

• Phylogenetic reconstruction to trace aas gene lineages across different Salmonella isolates

• Selection pressure analysis to identify regions under positive or purifying selection

WGS has demonstrated exceptional discriminatory power compared to traditional typing methods like PFGE, allowing researchers to differentiate highly clonal isolates and trace evolutionary relationships with high precision .

What are the common challenges in expressing soluble aas protein and how can they be addressed?

Expressing soluble Bifunctional protein aas presents several challenges due to its membrane-associated nature. Common issues and solutions include:

How can researchers validate that recombinant aas protein retains native conformation and activity?

Validating the native conformation and activity of recombinant aas protein requires multiple complementary approaches:

• Structural validation:

  • Circular dichroism (CD) spectroscopy to assess secondary structure

  • Thermal shift assays to determine protein stability

  • Limited proteolysis to probe folding state

  • Size exclusion chromatography to confirm monomeric/oligomeric state

• Functional validation:

  • Enzymatic activity assays comparing recombinant protein to native extracts

  • Lipid binding assays to confirm interaction with physiological substrates

  • Reconstitution into liposomes to test membrane integration

  • Complementation of aas-deficient Salmonella strains

• Immunological validation:

  • Western blotting with conformation-specific antibodies

  • ELISA to measure epitope accessibility

  • Surface plasmon resonance to quantify binding kinetics

Recombinant proteins expressed in E. coli systems, such as the His-tagged full-length aas protein described in the literature, should be tested for activity immediately after purification to establish a baseline for subsequent storage condition optimization .

How do variations in the aas gene correlate with Salmonella agona virulence and pathogenicity?

• Conserved genes like aas typically maintain core metabolic functions across strains

• Virulence is more commonly associated with pathogenicity islands, effector proteins, and mobile genetic elements

In studies of S. Agona isolates from various sources including canal water in Bangkok, all strains contained essential virulence factors associated with invasion, adhesion, and survival during infection, regardless of their antimicrobial resistance profiles . While specific aas gene variations have not been directly linked to virulence, the protein's role in membrane homeostasis could indirectly influence:

• Survival in hostile environments

• Resistance to host defense mechanisms

• Adaptation to specific infection niches

Comprehensive genomic and proteomic approaches combining WGS data with expression profiling would be required to establish definitive correlations between aas variants and virulence .

What bioinformatic pipelines best analyze aas gene presence and variation across Salmonella populations?

Based on approaches used in genomic studies of Salmonella, effective bioinformatic pipelines for analyzing aas gene presence and variation should include:

Studies of S. Agona outbreaks have demonstrated the value of such approaches, revealing that isolates from outbreaks separated by ten years differed by only a mean of eight SNPs, indicating direct descent rather than independent contamination events .

What is the potential of aas protein as a diagnostic biomarker for Salmonella agona detection?

The potential of aas protein as a diagnostic biomarker for S. Agona detection must be evaluated in the context of its conservation across Salmonella serovars. While highly conserved proteins make excellent targets for genus-level detection, they may lack serovar specificity. Nevertheless, aas protein offers several advantages as a diagnostic target:

• Stable expression: As a core metabolic protein, aas is likely constitutively expressed

• Structural accessibility: Surface-exposed epitopes could be targeted by antibodies

• Functional importance: Mutations would likely be deleterious, reducing false negatives

For serovar-specific detection, diagnostic assays would need to target:

• Serovar-specific variations within the aas gene

• Unique post-translational modifications

• Serovar-specific expression patterns

Methodologies similar to those used for epitope mapping of the FlgK protein, combining in silico prediction with experimental validation, could identify serovar-specific epitopes in the aas protein .

How might recombinant aas protein be utilized in vaccine development strategies against Salmonella?

The utilization of recombinant aas protein in vaccine development would follow approaches similar to those employed for other Salmonella proteins like FlgK. Strategic considerations include:

• Epitope identification:

  • Computational prediction of B-cell and T-cell epitopes

  • Experimental validation through animal immunization studies

  • Identification of conserved epitopes for broad protection

• Delivery platform selection:

  • Subunit vaccines containing purified recombinant protein

  • DNA vaccines encoding the aas gene

  • Viral vector vaccines expressing aas protein

  • Attenuated Salmonella strains with modified aas expression

• Adjuvant formulation:

  • Selection of appropriate adjuvants (e.g., Freund's incomplete adjuvant as used in FlgK studies)

  • Optimization of protein:adjuvant ratios

  • Development of novel delivery systems

• Immunization protocol optimization:

  • Determination of optimal dosage (e.g., 100 μg protein per dose)

  • Establishment of prime-boost schedules

  • Route of administration optimization

Studies with the FlgK protein demonstrated that subcutaneous administration of 100 μg recombinant protein in Freund's incomplete adjuvant, with a booster at three weeks, produced detectable antibody responses in broilers . Similar approaches could be applied to evaluate aas protein as a vaccine candidate.