Recombinant Pseudomonas syringae pv. syringae ATP synthase subunit b (atpF)

What is Pseudomonas syringae pv. syringae and why is it studied in plant pathology?

Pseudomonas syringae pv. syringae (Pss) is a plant pathogenic bacterium associated with diseases of numerous plant species. It belongs to phylogroup 2 within P. syringae sensu stricto and is notable for its environmental ubiquity and pathogenicity . Pss is extensively studied because it:

• Possesses a more pronounced epiphytic growth stage compared to other pathovars like P. syringae pv. tomato (Pst)

• Demonstrates higher abiotic stress tolerance

• Produces distinct phytotoxins, including syringomycin and syringopeptin

• Contains a 6.1 Mb genome with no plasmids (unlike Pst DC3000 which has a 6.5 Mb genome with two plasmids)

Pss strain B728a has been completely sequenced, revealing 976 unique protein-encoding genes when compared with Pst DC3000, including genomic islands likely contributing to virulence and host specificity .

What is ATP synthase subunit b (atpF) and what role does it play in bacterial metabolism?

ATP synthase subunit b (atpF) is a critical component of the bacterial F₀F₁-ATP synthase complex, which is responsible for ATP production through oxidative phosphorylation. While the search results don't provide specific details about atpF in P. syringae pv. syringae, we can infer its function based on general bacterial ATP synthase structure:

• The F₀ sector of ATP synthase spans the cytoplasmic membrane and contains subunits a, b, and c

• Subunit b forms part of the peripheral stalk connecting the membrane-embedded F₀ and the catalytic F₁ sectors

• It plays a crucial structural role in maintaining the stability of the ATP synthase complex during proton translocation and ATP synthesis

In P. syringae pv. tomato, the ATP synthase subunit b has been identified as PSPTO_5603, located in the cytoplasmic membrane and classified as part of the EV "core" proteome .

How do environmental conditions affect ATP synthase expression in P. syringae?

ATP synthase expression in P. syringae appears to be regulated in response to environmental conditions, though specific data on atpF is limited. Research findings suggest:

• Gene expression patterns in P. syringae differ between in vitro and in planta conditions, including genes related to energy metabolism

• P. syringae adapts its metabolism during different lifestyle stages (epiphytic vs. apoplastic)

• Energy production genes may be differentially expressed during plant infection compared to laboratory culture conditions

• ATP synthase components in P. syringae pv. tomato appear in the core proteome of extracellular vesicles (EVs), suggesting a role in bacterial adaptation to various environments

What are effective methods for cloning and expressing recombinant P. syringae proteins?

Based on methodologies described for other P. syringae proteins, the following approaches are recommended for atpF:

Cloning strategies:

• Amplify the atpF ORF from P. syringae pv. syringae genomic DNA

• Clone into an appropriate expression vector (pET for His-tagged proteins or pGEX for GST-tagged proteins)

• Transform into a suitable E. coli expression strain like BL21

Expression conditions:

• Induce at 16-28°C with 0.2-0.5 mM IPTG

• For membrane proteins like atpF, lower induction temperatures (16°C) for 10+ hours may improve proper folding

• Consider using specialized E. coli strains designed for membrane protein expression

What purification methods are most effective for recombinant ATP synthase components?

For purification of His-tagged recombinant atpF:

• Collect bacterial cells after induction and resuspend in buffer (PBS with 1 mM PMSF)

• Lyse cells by sonication and centrifuge at 12,000 g for 30 min at 4°C

• Load supernatant onto a Ni-NTA His-Bind Resin column pre-equilibrated with PBS

• Wash with PBS and elute with a gradient of 100-500 mM imidazole in PBS

For GST-tagged proteins:

• Induce expression at 28°C with 0.5 mM IPTG for 5 hours

• Sonicate bacterial pellet in PBS at 4°C

• Incubate supernatant with GST-Bind Resin for 3 hours at 4°C

• Elute using buffer containing 20 mM reduced glutathione

• Concentrate by centrifugation and assess by SDS-PAGE

How can researchers verify the structure and function of purified recombinant atpF?

To verify the structural integrity and function of recombinant atpF:

Structural verification:

• SDS-PAGE analysis to confirm protein size and purity

• Western blot with anti-His or anti-GST antibodies to verify tag presence

• Circular dichroism (CD) spectroscopy to assess secondary structure elements

• Mass spectrometry to confirm protein identity and detect post-translational modifications

Functional assays:

• ATP hydrolysis assays to measure ATPase activity

• Reconstitution into liposomes to assess membrane insertion capability

• Proteoliposome-based proton translocation assays

• Protein-protein interaction studies with other ATP synthase components using pull-down assays or co-immunoprecipitation

How might atpF function relate to P. syringae virulence mechanisms?

While direct evidence linking atpF to virulence is limited, several possible connections can be investigated based on current knowledge:

• Energy requirements for virulence factor synthesis:

  • Production of phytotoxins like syringomycin, syringopeptin, and coronatine requires substantial energy resources

  • ATP synthase function may be critical for generating the ATP needed for toxin biosynthesis

• Support for secretion systems:

  • The Type III Secretion System (T3SS) is ATP-dependent, suggesting ATP synthase activity may indirectly affect virulence

  • Effector proteins secreted through T3SS play crucial roles in P. syringae pathogenicity

• Adaptation to plant environments:

  • ATP synthase may be important for bacterial adaptation to varying conditions in plant tissues

  • ATP production could support stress responses during plant colonization

Research approaches to investigate these connections might include:

• Creating atpF mutants and assessing their virulence

• Measuring ATP levels during infection and correlating with virulence factor production

• Investigating atpF expression patterns during different stages of plant infection

How do ATP synthase components compare across different P. syringae pathovars?

Comparative analysis of ATP synthase components across P. syringae pathovars could reveal:

• Sequence conservation patterns that might indicate functional constraints

• Pathovar-specific adaptations related to host range or environmental niches

• Potential horizontal gene transfer events affecting energy metabolism genes

Genome comparison studies between P. syringae pathovars have revealed:

• Substantial genomic diversity between pathovars

• Evidence of homologous recombination affecting core genome functions

• Enrichment of recombination in pathways involved in ATP-dependent transport and metabolism of amino acids

A comprehensive phylogenetic analysis of atpF sequences across P. syringae lineages could provide insights into:

• The evolutionary history of ATP synthase components

• Selection pressures acting on energy metabolism genes

• Potential co-evolution with virulence factors

What experimental approaches can assess the role of atpF in bacterial fitness?

To evaluate the contribution of atpF to P. syringae fitness:

Genome-wide fitness profiling:

• Create a randomly barcoded transposon mutant library in P. syringae

• Grow mutants under different conditions (epiphytic vs. apoplastic)

• Use high-throughput sequencing to identify fitness-contributing genes

Mutant characterization:

• Generate atpF deletion or point mutants

• Assess growth rates under various conditions (minimal vs. rich media)

• Measure competitive fitness in mixed populations with wild-type strains

• Evaluate survival under stress conditions relevant to plant environments

In planta studies:

• Inoculate plants with atpF mutants and wild-type strains

• Compare bacterial population sizes over time

• Assess disease symptom development

• Measure ATP levels in bacterial cells recovered from plants

One study using genome-wide fitness profiling of P. syringae identified genes contributing to fitness both on leaf surfaces and in the apoplast, with amino acid and polysaccharide biosynthesis genes being particularly important in both environments .

How might studying ATP synthase inform novel antimicrobial strategies?

Investigating ATP synthase subunit b could lead to novel antimicrobial approaches:

• Target-based drug design:

  • ATP synthase is essential for bacterial energy production

  • Structural differences between bacterial and plant ATP synthases could be exploited for selective inhibition

  • Compounds targeting the b subunit might disrupt the peripheral stalk, inhibiting ATP production

• Virulence attenuation:

  • Partial inhibition of ATP synthase might reduce virulence without strong selection for resistance

  • This could be particularly effective against energy-intensive virulence mechanisms like toxin production

• Combination strategies:

  • ATP synthase inhibitors might synergize with existing antimicrobials

  • Targeting energy production could sensitize bacteria to other stresses

What methodologies can address the challenge of membrane protein crystallization for structural studies?

Structural studies of membrane proteins like atpF face significant challenges:

Advanced crystallization techniques:

• Lipidic cubic phase (LCP) crystallization

• Bicelle crystallization methods

• Detergent screening to find optimal solubilization conditions

• Use of antibody fragments or nanobodies to stabilize protein conformations

Alternative structural biology methods:

• Cryo-electron microscopy (cryo-EM) for high-resolution structures without crystallization

• NMR spectroscopy for dynamic studies of smaller membrane protein domains

• Molecular dynamics simulations based on homology models

Protein engineering approaches:

• Fusion with crystallization chaperones

• Thermostabilizing mutations

• Removal of flexible regions that might hinder crystallization

How can systems biology approaches integrate ATP synthase function into broader metabolic networks?

Systems biology offers powerful frameworks to understand atpF in the context of P. syringae metabolism:

Multi-omics integration:

• Combine transcriptomics, proteomics, and metabolomics data to map energy flux during infection

• Correlate ATP synthase expression with virulence factor production

• Identify metabolic bottlenecks during different growth phases

Computational modeling:

• Develop genome-scale metabolic models incorporating ATP synthase activity

• Simulate the effects of perturbations to energy metabolism

• Predict metabolic adaptations during host colonization

Network analysis:

• Map protein-protein interactions involving ATP synthase components

• Identify regulatory networks controlling energy metabolism

• Discover potential functional links between ATP synthase and virulence factors

One study identified clusters of genes in P. syringae pv. tomato with coordinated expression patterns across different conditions, including genes involved in ATP synthesis . These clusters could provide insights into how energy metabolism is integrated with other cellular processes during pathogenesis.

Comparison of ATP Synthase Components Across Pseudomonas Species

Methods for Recombinant Protein Production from P. syringae

Virulence Factors in P. syringae Requiring Energy from ATP Synthase Activity