Recombinant Salmonella newport Bifunctional protein aas (aas)

What is the bifunctional protein AAS in Salmonella Newport and what are its primary functions?

The bifunctional protein AAS (2-acylglycerophosphoethanolamine acyltransferase/acyl-ACP synthetase) in Salmonella Newport performs dual enzymatic functions in phospholipid metabolism and fatty acid activation. Its acyltransferase activity facilitates membrane phospholipid remodeling, while its synthetase activity activates exogenous fatty acids for incorporation into membrane phospholipids. These functions are critical for bacterial membrane homeostasis, particularly under environmental stress conditions similar to those that activate RpoS-dependent stress responses . The functionality of AAS contributes to Salmonella Newport's adaptability across varying environmental conditions, potentially enhancing survival in non-host environments.

How does genetic diversity in Salmonella Newport impact AAS protein structure and function?

Salmonella Newport demonstrates significant genetic diversity with at least four distinct sublineages showing geographic distribution patterns . This genetic diversity extends to genes involved in metabolic functions, including those related to membrane integrity. While AAS is relatively conserved across Salmonella species, the genetic flow and homologous recombination events observed in S. Newport lineages II and III suggest potential variation in regulatory elements affecting AAS expression . Researchers should account for strain-specific differences when studying AAS function, as genetic variations between lineages may influence protein expression levels, substrate specificity, or regulatory control mechanisms. When conducting experimental studies with recombinant AAS, the source lineage should be clearly documented to ensure reproducibility.

What expression systems are most effective for producing recombinant Salmonella Newport AAS protein?

For successful expression of recombinant S. Newport AAS protein, E. coli-based expression systems (particularly BL21(DE3) strains) offer high yields and simplified purification when coupled with appropriate affinity tags. Key methodological considerations include:

• Codon optimization for E. coli expression, particularly important given the divergent codon usage between Salmonella and E. coli

• Use of inducible promoters (such as T7) with careful optimization of induction parameters (temperature, inducer concentration, induction time)

• Fusion with solubility-enhancing tags (such as SUMO, MBP, or TrxA) to reduce inclusion body formation

• Growth conditions that mimic stress responses similar to those activating RpoS-dependent pathways may improve functional expression

For membrane-associated proteins like AAS, expression conditions that promote proper folding rather than maximum yield often produce more functionally active protein. Lowering expression temperature to 18-20°C post-induction and inclusion of appropriate detergents during purification are recommended to maintain protein functionality.

What are the optimal conditions for assessing AAS enzymatic activity in Salmonella Newport strains with varying stress response capabilities?

The bifunctional activity of AAS requires distinct assay conditions for each enzymatic function. Based on studies of wild-type and rpoS-deficient S. Newport strains, optimal assessment requires:

When assessing AAS activity in different S. Newport strains, researchers should consider that rpoS-deficient strains show altered stress responses that may indirectly affect AAS activity . Comparison between wild-type and ΔrpoS strains reveals that stress response capability significantly impacts membrane lipid composition under challenging environmental conditions. Activity assays should incorporate physiologically relevant stress conditions (nutrient limitation, pH stress, or temperature variation) to accurately assess functional differences between strains .

How can site-directed mutagenesis be used to investigate the functional domains of recombinant Salmonella Newport AAS?

Site-directed mutagenesis provides powerful insights into AAS structure-function relationships. The recommended approach includes:

• Target selection: Focus on conserved residues in the two catalytic domains—typically histidine, aspartate, and serine residues in the acyltransferase domain and lysine and arginine residues in the synthetase ATP-binding domain

• Mutagenesis approach: Employ overlap extension PCR or commercial mutagenesis kits (e.g., QuikChange) with the following parameters:

  • Primer design: 25-35 nucleotides with the mutation centrally positioned

  • Extension temperature: 68°C for high-fidelity polymerases

  • Template removal: DpnI digestion (3-4 hours at 37°C)

• Functional analysis: Compare wild-type and mutant proteins through:

  • Individual activity assays for each enzymatic function

  • Thermal stability analysis to detect structural perturbations

  • Substrate binding studies using isothermal titration calorimetry or surface plasmon resonance

This approach has revealed that while the two functional domains of AAS are structurally distinct, mutations in one domain can allosterically affect the other domain's activity, suggesting interdomain communication critical for the protein's bifunctionality. This methodology provides insights into how evolutionarily divergent S. Newport lineages may have developed functional variations in AAS .

What techniques are most effective for studying the role of AAS in Salmonella Newport's adaptation to environmental stressors?

Studying AAS's role in environmental adaptation requires integrating multiple experimental approaches:

• Comparative genomics and transcriptomics:

  • Whole genome sequencing across S. Newport lineages to identify natural AAS variants

  • RNA-seq under varying environmental conditions to determine stress-responsive AAS expression patterns

• In vitro survival assays:

  • Growth curve analysis in soil extracts with varying amendments, comparing wild-type and AAS-deficient strains

  • Measurement of lag time (λ), maximum growth rate (μmax), and maximum population density (Nmax) parameters

  • Competition assays with indigenous microbes in nonsterile environmental samples

• Membrane integrity analysis:

  • Fluorescent membrane staining (e.g., DiBAC4(3), propidium iodide) to assess membrane potential and permeability

  • Lipidomics to determine phospholipid composition changes under stress conditions

• In vivo colonization studies:

  • Animal models to assess virulence and colonization capacity of AAS mutants

  • Competitive index determination between wild-type and AAS-deficient strains

Research on rpoS-deficient S. Newport strains has demonstrated that stress response capabilities significantly impact environmental survival . Similar methodologies applied to AAS-modified strains would elucidate this protein's specific contribution to stress adaptation and environmental persistence.

How does AAS contribute to Salmonella Newport's antibiotic resistance phenotypes?

The bifunctional AAS protein may contribute to antibiotic resistance through membrane remodeling that affects permeability barriers. Studies of multidrug-resistant S. Newport strains like REPJJP01 suggest correlations between membrane composition and resistance profiles. The methodological approach to investigate this relationship involves:

• Generation of AAS knockout, overexpression, and site-directed mutant strains in antibiotic-resistant backgrounds

• Comparative minimum inhibitory concentration (MIC) determination across strain variants

• Membrane fluidity assessment using fluorescence anisotropy

• Analysis of outer membrane protein composition and lipid A modifications

• Efflux pump activity measurements using fluorescent substrates

Recent data indicates that AAS activity may influence the incorporation of exogenous fatty acids into membrane phospholipids, potentially altering membrane fluidity and permeability to antibiotics. This membrane remodeling activity appears particularly important in environmental conditions that trigger stress responses, similar to those that activate RpoS-dependent pathways .

What is the relationship between AAS function and Salmonella Newport persistence in agricultural environments?

Investigation of AAS's role in environmental persistence requires experimental approaches that simulate agricultural conditions:

• Soil extract survival assays:

  • Preparation of sterile and nonsterile soil extracts with various amendments

  • Inoculation with wild-type and AAS-deficient S. Newport strains

  • Monitoring population dynamics over time (0-96 hours)

• Environmental stress modeling:

  • Temperature fluctuation (4-37°C)

  • Desiccation and rehydration cycles

  • Nutrient limitation and competition with indigenous microbiota

• Genetic stability assessment:

  • Long-term passage under selective conditions

  • Whole genome sequencing to identify compensatory mutations

Data from studies with rpoS-deficient strains indicate that stress response capability significantly impacts survival in soil environments . AAS likely contributes to this persistence through maintenance of membrane integrity under stress conditions. In amended soil extracts, wild-type strains show significantly higher maximum population densities (Nmax) compared to stress-response deficient strains, suggesting that proteins involved in membrane homeostasis, including AAS, play key roles in environmental adaptation .

How does Salmonella Newport AAS compare structurally and functionally to homologous proteins in other Salmonella serovars?

Comparative analysis of AAS across Salmonella serovars provides evolutionary insights and functional predictions. Methodological approaches include:

• Sequence analysis:

  • Multiple sequence alignment of AAS proteins from diverse Salmonella serovars

  • Calculation of conservation scores for catalytic and substrate-binding residues

  • Identification of serovar-specific sequence variations

• Structural comparison:

  • Homology modeling based on crystallographic structures of related proteins

  • Molecular dynamics simulations to identify conformational differences

  • Virtual screening for serovar-specific inhibitors

• Functional characterization:

  • Heterologous expression of AAS variants from different serovars

  • Enzymatic activity comparison under standardized conditions

  • Complementation studies in AAS-deficient backgrounds

The genetic diversity observed across S. Newport lineages suggests that AAS may have undergone serovar-specific adaptations . Whole genome sequencing has revealed that S. Newport lineages II and III diverged early in serotype evolution and have evolved largely independently, potentially leading to functional specialization of proteins like AAS that are involved in environmental adaptation .

What methodologies are recommended for identifying the role of AAS in the genetic diversification of Salmonella Newport lineages?

The genetic diversification of S. Newport lineages provides a natural experiment for studying AAS evolution. Recommended methodologies include:

• Phylogenomic analysis:

  • Whole genome sequencing of diverse S. Newport isolates

  • Identification of single nucleotide polymorphisms (SNPs) within and surrounding the aas gene

  • Analysis of selective pressure (dN/dS ratios) on the aas coding sequence

• Recombination detection:

  • Statistical methods to identify recombination events affecting the aas locus

  • Comparison with recombination patterns observed around other genes (e.g., mutS)

  • Analysis of mobile genetic elements in proximity to aas

• Expression profiling:

  • qRT-PCR analysis of aas expression across lineages

  • Identification of lineage-specific regulatory elements

  • Characterization of transcription factor binding sites

• Functional comparison:

  • Cloning and expression of aas variants from different lineages

  • Enzymatic activity comparison under various environmental conditions

  • Complementation of aas deficiency across lineage backgrounds

The observed genetic flow and homologous recombination events around genes like mutS in S. Newport lineages II and III provide a model for studying similar evolutionary processes affecting functional genes like aas . Such studies can reveal how selective pressures in different environmental niches have shaped protein function across evolutionary time.

What are the most common challenges in purifying active recombinant Salmonella Newport AAS protein and how can they be overcome?

Purification of functional recombinant AAS presents several technical challenges due to its bifunctional nature and membrane association. Common issues and solutions include:

The multifunctional nature of AAS makes activity preservation particularly challenging. Researchers should implement activity assays at each purification step to track retention of both enzymatic functions, as conditions that preserve one activity may compromise the other. Successful purification typically requires a balance between yield and functional preservation rather than maximizing protein quantity.

How can researchers effectively design experiments to study AAS function in the context of Salmonella Newport's complex stress response networks?

Studying AAS within stress response networks requires integrating multiple approaches:

• Genetic interaction mapping:

  • Construction of dual mutants (aas with stress response genes)

  • Synthetic genetic array analysis to identify epistatic relationships

  • Complementation studies with controlled expression systems

• Protein-protein interaction studies:

  • Bacterial two-hybrid screening

  • Co-immunoprecipitation followed by mass spectrometry

  • Proximity labeling techniques (BioID, APEX) adapted for bacterial systems

• Multi-omics integration:

  • Parallel analysis of transcriptome, proteome, and lipidome

  • Network analysis to position AAS within stress response pathways

  • Perturbation studies with environmental stressors

• Time-resolved experiments:

  • Sampling across stress exposure timeline

  • Pulse-chase labeling of newly synthesized proteins

  • Real-time monitoring of membrane integrity

Studies of rpoS-deficient S. Newport strains have demonstrated the complex interplay between stress response genes and environmental adaptation . Similar methodologies can position AAS within these networks by examining how its function changes under conditions that activate RpoS-dependent and independent stress responses. This approach has revealed that proteins involved in membrane homeostasis often function cooperatively within larger stress response networks rather than independently.

What emerging technologies show promise for advancing understanding of AAS function in Salmonella Newport pathogenesis and environmental persistence?

Several emerging technologies offer new approaches to studying AAS function:

• CRISPR interference (CRISPRi) and activation (CRISPRa):

  • Tunable repression or activation of aas expression

  • Tissue-specific or condition-specific modulation in infection models

  • Multiplexed targeting of aas alongside related genes

• Single-cell technologies:

  • Microfluidic systems for monitoring individual bacterial responses

  • Single-cell RNA-seq to capture population heterogeneity

  • Time-lapse microscopy with fluorescent membrane reporters

• Advanced structural biology approaches:

  • Cryo-electron microscopy for membrane protein structures

  • Hydrogen-deuterium exchange mass spectrometry for conformational dynamics

  • Integrative structural modeling combining multiple data sources

• In situ techniques:

  • RNA-FISH for visualizing aas expression in infected tissues

  • Advanced imaging mass spectrometry for lipid localization

  • In vivo biosensors for real-time monitoring of bacterial metabolism

These technologies would allow researchers to address questions about how AAS function varies across S. Newport lineages with different pathogenic potential and environmental persistence capabilities . For example, studies of the persistent REPJJP01 strain might reveal specific adaptations in AAS function that contribute to this strain's success in diverse environments .

How can research on Salmonella Newport AAS contribute to broader understanding of bacterial adaptation and evolution?

Research on S. Newport AAS offers insights into fundamental biological processes:

• Evolutionary biology:

  • Model for studying functional diversification after gene duplication

  • Insights into adaptation to new ecological niches

  • Understanding of selection pressures on multifunctional proteins

• Host-pathogen interactions:

  • Mechanisms of bacterial adaptation to host environments

  • Evolution of virulence traits from environmental adaptation mechanisms

  • Lipid metabolism as a nexus between virulence and persistence

• Systems biology:

  • Integration of metabolism with stress responses

  • Network properties of multifunctional proteins

  • Robustness and plasticity in bacterial regulatory systems

• Biophysics of membrane systems:

  • Lipid-protein interactions under environmental stress

  • Principles of membrane homeostasis

  • Mechanisms of membrane remodeling in response to external stimuli

The distinct evolutionary trajectories of S. Newport lineages provide a natural experiment for studying how bifunctional proteins like AAS evolve under different selective pressures . Combined with the strain's ability to persist in diverse environments , this makes S. Newport AAS an excellent model for understanding the molecular basis of bacterial adaptation and evolution.