Recombinant Pseudomonas syringae pv. phaseolicola ATP synthase subunit a (atpB)

What is the basic structure and function of ATP synthase subunit a (atpB) in Pseudomonas syringae pv. phaseolicola?

ATP synthase subunit a (atpB) in P. syringae pv. phaseolicola is a 289-amino acid membrane protein that forms part of the F0 sector of ATP synthase, which is critical for proton translocation across the membrane during ATP synthesis . The protein contains hydrophobic regions that anchor it in the membrane, with specific residues involved in the proton channel. Its primary function is to participate in creating a proton gradient that drives ATP synthesis, which is essential for bacterial energy metabolism. The complete amino acid sequence is: MAEQTASGYIQHHLQNLTFGHLPNGEWGFAHTAAEAKEMGFWAFHVDTLGWSVALGLIFVLIFRMAAKKATSGQPGALQNFVEVLVDFVDGSVKDSFHGRSAVIAPLALTIFVWVFLMNAVDLVPVDWIPQLAMLISGDEHIPFRAVPTTDPNATLGMALSVFALIIFYSIKVKGIGGFIGELTLHPFGSKNLFVQALLIPVNFLLEFVTLIAKPISLALRLFGNMYAGELVFILIAVMFGSGLLWLSGLGVVLQWAWAVFHILIITLQAFIFMMLTIVYLSMAHEDNH .

What are the synonyms and alternative designations for the atpB gene and protein?

The atpB gene in P. syringae pv. phaseolicola has several alternative designations in research literature and databases. The gene is officially named atpB with the locus tag PSPPH_5213 in strain 1448A/Race 6 . The protein product has multiple alternative names including: ATP synthase subunit a, ATP synthase F0 sector subunit a, and F-ATPase subunit 6 . In research papers and databases, you may find it referenced under any of these names, with the UniProt accession number Q48BF9 providing a definitive identifier . Understanding these alternative designations is crucial when conducting literature searches or comparing sequences across different bacterial species.

How is recombinant atpB typically produced for research purposes?

Recombinant atpB from P. syringae pv. phaseolicola is typically produced in E. coli expression systems using molecular cloning techniques . The full-length protein (amino acids 1-289) is often expressed with affinity tags, most commonly an N-terminal His-tag, to facilitate purification . The recombinant protein is purified using affinity chromatography, typically followed by SDS-PAGE verification to confirm purity (>90%) . The purified protein is then lyophilized for stable storage or maintained in a Tris-based buffer with glycerol to prevent degradation . E. coli-based expression systems are preferred due to their high yield and ease of genetic manipulation, although membrane proteins like atpB can sometimes form inclusion bodies, requiring optimization of expression conditions.

What are the optimal storage and handling conditions for recombinant atpB protein?

Optimal storage and handling of recombinant atpB requires careful attention to prevent protein degradation and maintain structural integrity. The lyophilized protein should be stored at -20°C to -80°C upon receipt . For working solutions, the protein should be reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL, with the addition of 5-50% glycerol (typically 50%) as a cryoprotectant . Reconstituted protein should be aliquoted to avoid repeated freeze-thaw cycles, which can significantly compromise protein structure and function . Working aliquots can be stored at 4°C for up to one week . When handling the protein, maintain sterile conditions and use low-protein binding tubes to minimize loss through adsorption. For long-term studies, stability tests using activity assays or structural analysis methods should be performed periodically to verify protein integrity.

How should researchers reconstitute lyophilized atpB for experimental use?

The reconstitution of lyophilized atpB requires careful attention to detail to ensure optimal protein recovery and activity. Before opening, briefly centrifuge the vial containing lyophilized protein to bring all contents to the bottom . Reconstitute the protein in deionized sterile water to achieve a concentration between 0.1-1.0 mg/mL . For membrane proteins like atpB, addition of a detergent (such as 0.1% DDM or 0.5% CHAPS) may be necessary to maintain solubility, though this is not explicitly mentioned in the product descriptions. Add glycerol to a final concentration of 5-50% (typically 50% is recommended) to enhance stability . Gently mix the solution by inversion rather than vortexing to prevent protein denaturation. Allow the protein to fully dissolve at room temperature for 15-30 minutes before aliquoting for storage. Verify protein concentration using Bradford or BCA assays, accounting for any interference from buffer components.

What analytical methods are most effective for confirming the purity and integrity of recombinant atpB?

Multiple analytical techniques should be employed to comprehensively assess the purity and integrity of recombinant atpB. SDS-PAGE is the primary method for purity assessment, with commercial preparations typically showing >90% purity . Western blotting using anti-His antibodies can confirm the presence of the His-tagged protein . Mass spectrometry (particularly LC-MS/MS) provides the most precise verification of protein identity and can detect potential post-translational modifications or truncations. For structural integrity, circular dichroism (CD) spectroscopy can assess secondary structure elements characteristic of membrane proteins. Size-exclusion chromatography can detect aggregation states, which is particularly important for membrane proteins prone to aggregation. Functional assays measuring ATPase activity or proton translocation can confirm that the protein maintains its native conformation. For highest confidence, a combination of these techniques should be employed when establishing new experimental protocols using recombinant atpB.

How can researchers investigate the role of atpB in pathogenicity of Pseudomonas syringae pv. phaseolicola?

Investigating atpB's potential role in P. syringae pv. phaseolicola pathogenicity requires a multi-faceted approach. Gene knockout or knockdown studies using CRISPR-Cas9 or RNA interference can establish whether atpB is essential for bacterial virulence . Complementation assays can confirm phenotypes observed in knockout strains. Transcriptome analysis comparing gene expression in bacteria grown in minimal media versus plant extracts can reveal whether atpB is differentially regulated during plant infection, similar to studies that have identified other virulence factors . While atpB wasn't specifically mentioned among differentially expressed genes in the provided transcriptional profile study, similar approaches could reveal its regulation under different conditions . Protein-protein interaction studies can identify whether atpB interacts with known virulence factors or plant immune receptors. Plant infection assays using atpB mutants can directly assess effects on disease progression. Comparative studies across different P. syringae pathovars may reveal pathovar-specific atpB functions related to host specificity.

What structural and functional differences exist between atpB from P. syringae pv. phaseolicola and other bacterial species?

Structural and functional comparison of atpB across bacterial species reveals both conserved domains and species-specific adaptations. Sequence alignment tools should be used to compare the 289-amino acid sequence of P. syringae pv. phaseolicola atpB with homologs from other bacteria, particularly other plant pathogens and non-pathogenic Pseudomonads . Key comparisons should focus on the transmembrane domains and residues known to participate in proton translocation. Homology modeling using solved ATP synthase structures (typically from E. coli or mycobacterial species) can predict structural differences. Functional differences can be assessed through complementation studies, where atpB from different species is expressed in an atpB-deficient strain. Biochemical assays comparing proton translocation efficiency or ATP synthesis rates can identify functional differences. Thermal stability assays may reveal adaptations to different environmental conditions. Evolutionary analysis using phylogenetic trees can help understand the relationship between sequence variation and bacterial lifestyle or host range.

How can site-directed mutagenesis of atpB help understand its structure-function relationship?

Site-directed mutagenesis provides powerful insights into atpB structure-function relationships by allowing precise modification of key residues. Based on the amino acid sequence, researchers should target conserved residues in transmembrane domains that likely participate in proton translocation . Mutations of charged residues (particularly arginines and glutamates) within these domains can disrupt the proton pathway. Alanine scanning mutagenesis, systematically replacing residues with alanine, can identify functionally important regions. Mutations at the interface with other ATP synthase subunits can reveal details about subunit interactions. After generating mutants, functional assays should measure effects on proton translocation, ATP synthesis rates, and membrane association. Structural studies of mutant proteins using techniques like cryo-electron microscopy can visualize conformational changes. In vivo studies in bacterial cells can connect biochemical changes to physiological effects. Comparing the effects of equivalent mutations across different bacterial species can highlight evolutionary conservation versus species-specific adaptations.

What are the most effective expression systems for producing functional recombinant atpB?

Optimizing expression systems for membrane proteins like atpB requires careful consideration of host strain, expression vectors, and induction conditions. E. coli is the most commonly used expression host for recombinant atpB, particularly BL21(DE3) strains or derivatives like C41/C43 that are engineered for membrane protein expression . For challenging membrane proteins, consider alternative expression systems such as Lactococcus lactis or cell-free systems that can reduce toxicity and inclusion body formation. Expression vectors with tunable promoters (like pET series with T7lac promoter) allow control over expression levels, which is critical for membrane proteins where overexpression can be toxic . Low-temperature induction (16-18°C) with reduced IPTG concentrations (0.1-0.5 mM) often improves proper folding. Co-expression with chaperones like GroEL/GroES can enhance correct folding. Addition of specific lipids or detergents to the growth medium may improve membrane insertion. For purification, consider using mild detergents like DDM or LMNG that maintain protein stability and function. Functional assays should verify that the recombinant protein maintains native activity.

How can researchers design experiments to study atpB interactions with other ATP synthase subunits?

Studying atpB interactions with other ATP synthase subunits requires specialized approaches for membrane protein complexes. Co-immunoprecipitation using antibodies against the His-tag on recombinant atpB can pull down interacting partners . Crosslinking studies using chemical crosslinkers with defined spacer lengths can capture transient interactions. Bacterial two-hybrid systems or split-reporter assays adapted for membrane proteins can detect binary interactions. For more comprehensive analysis, Blue Native PAGE can resolve intact ATP synthase complexes and identify subcomplexes. Mass spectrometry-based approaches like hydrogen-deuterium exchange or chemical crosslinking coupled with MS can map interaction interfaces at the residue level. Structural studies using cryo-electron microscopy can visualize the entire ATP synthase complex, with single-particle analysis revealing conformational states. Reconstitution of purified subunits into liposomes or nanodiscs allows functional studies of defined subunit combinations. Genetic approaches using suppressor mutations can identify functionally interacting residues between subunits. These complementary approaches provide a comprehensive view of atpB's role within the ATP synthase complex.

What controls should be included when performing functional assays with recombinant atpB?

Rigorous control experiments are essential for reliable functional assays with recombinant atpB. Positive controls should include commercially available ATP synthase components with verified activity . Negative controls should include denatured atpB protein (heat-treated) and buffer-only samples to establish baseline measurements. Species-specific controls comparing recombinant atpB to native P. syringae pv. phaseolicola membrane preparations can validate recombinant protein function. When measuring proton translocation, ionophores like CCCP can serve as positive controls for membrane permeabilization. For ATPase activity assays, specific inhibitors like oligomycin or DCCD can confirm ATP synthase-specific activity. pH controls are critical for proton translocation assays, with carefully established pH gradients. Temperature controls should be included, particularly if comparing atpB from different bacterial species adapted to different environments. When reconstituting atpB into liposomes, controls for protein orientation (inside-out vs. right-side-out) are necessary. Statistical validation requires multiple independent protein preparations and technical replicates to account for batch-to-batch variation.

How does atpB expression change during infection and in response to plant-derived signals?

Analyzing changes in atpB expression during infection provides insights into its potential role in plant-pathogen interactions. Transcriptome studies, such as those performed with P. syringae pv. phaseolicola grown in plant extracts, can reveal whether atpB is differentially regulated during infection . While the specific transcriptional profile study in the search results didn't highlight atpB among differentially expressed genes, similar methodologies can be applied to various conditions . Researchers should design experiments comparing atpB expression across multiple infection stages and in response to different plant extracts (leaf, pod, apoplastic fluid) . Quantitative RT-PCR can provide precise measurements of atpB transcript levels under different conditions. Promoter-reporter fusions (e.g., atpB promoter driving GFP expression) can visualize expression patterns in real-time during infection. Proteomic approaches can determine whether transcript-level changes translate to protein abundance differences. Comparative analysis with other ATP synthase subunits can reveal whether the entire complex is co-regulated or if atpB shows distinct expression patterns. Integration with metabolomic data measuring ATP levels and membrane potential can connect expression changes to physiological states.

What is the relationship between atpB function and bacterial stress responses in P. syringae pv. phaseolicola?

ATP synthase activity is intrinsically linked to bacterial stress responses, making atpB a potential stress response regulator. Researchers should investigate how environmental stressors relevant to plant infection (pH changes, oxidative stress, osmotic stress) affect atpB expression and ATP synthase function. Transcriptome analysis can reveal co-regulation of atpB with known stress response genes . Metabolic studies measuring ATP/ADP ratios under stress conditions can connect atpB function to energy homeostasis during stress. Membrane potential measurements using voltage-sensitive dyes can assess how atpB function relates to proton motive force maintenance during stress. Genetic approaches using atpB knockdown or overexpression can determine whether modulating atpB levels affects stress tolerance. Comparative studies between virulent and avirulent strains may reveal stress response differences related to ATP synthesis. Proteomic approaches focusing on post-translational modifications can identify regulatory mechanisms affecting atpB during stress. Researchers should pay particular attention to iron limitation stress, as iron-related genes showed significant repression in plant extract conditions, possibly affecting iron-dependent metabolic processes including respiration and ATP synthesis .

How can structural information about atpB inform the development of novel antimicrobials targeting P. syringae pv. phaseolicola?

Structural insights into atpB can guide rational design of antimicrobials targeting ATP synthase in P. syringae pv. phaseolicola. Homology modeling using the amino acid sequence and known ATP synthase structures can predict the three-dimensional structure of atpB . Molecular docking studies can identify potential binding pockets unique to the bacterial protein compared to plant homologs. Structure-based virtual screening of chemical libraries can identify candidate inhibitors targeting these unique pockets. Functional assays measuring ATP synthesis inhibition can validate computational predictions. Site-directed mutagenesis of predicted binding sites can confirm the mechanism of action of candidate compounds. Crystallography or cryo-electron microscopy of atpB-inhibitor complexes can provide precise structural information for iterative optimization. Whole-cell assays measuring antimicrobial activity against P. syringae pv. phaseolicola can assess cell permeability and in vivo efficacy. Plant infection studies can determine whether candidates reduce disease severity. Selectivity assays comparing inhibition of bacterial versus plant ATP synthases are crucial to develop compounds safe for agricultural application. Integration with pathogenicity studies can provide dual-targeting opportunities where compounds might simultaneously inhibit ATP synthesis and virulence mechanisms.

What are the most common pitfalls when working with recombinant atpB and how can they be addressed?

Researchers frequently encounter challenges when working with membrane proteins like atpB, requiring specific troubleshooting approaches. Low expression yields in recombinant systems can be addressed by optimizing codon usage for the expression host, reducing induction temperature, or trying specialized strains like C41/C43 . Protein aggregation or inclusion body formation may require screening different detergents for solubilization or using fusion partners that enhance solubility. Loss of activity during purification often occurs due to detergent-induced conformational changes; try milder detergents or lipid nanodiscs to maintain the native lipid environment. Protein degradation can be minimized by including protease inhibitors throughout purification and storing with glycerol at appropriate temperatures . Inconsistent results between batches necessitate stringent quality control protocols including activity assays and structural verification for each preparation. Non-specific binding in interaction studies requires careful blocking strategies and appropriate negative controls. When reconstituting into liposomes, protein orientation can be random; techniques like protease protection assays can determine orientation. Functional assays may show high background; optimize buffer compositions and include appropriate controls to establish signal-to-noise ratios.

How can researchers differentiate between direct and indirect effects when studying atpB knockout phenotypes?

Differentiating direct from indirect effects in atpB knockout studies requires comprehensive experimental design and multiple controls. Complementation assays, where wild-type atpB is reintroduced into knockout strains, should restore wild-type phenotypes if effects are direct . Site-directed mutagenesis targeting specific functional domains can create partial loss-of-function variants that help dissect which phenotypes are linked to specific atpB functions. Inducible knockout systems allow temporal control of atpB depletion, helping distinguish primary effects from secondary adaptations. Metabolomic profiling can identify immediate metabolic changes following atpB depletion before compensatory mechanisms engage. Transcriptome analysis comparing early and late responses to atpB knockout can separate direct regulatory effects from downstream consequences . Protein-protein interaction studies can identify direct binding partners potentially responsible for observed phenotypes. Chemical genetic approaches using specific ATP synthase inhibitors can complement genetic knockouts and help establish cause-effect relationships. Multi-omics integration combining proteomics, transcriptomics, and metabolomics provides a systems-level view to distinguish direct effects from network adaptations. When studying virulence phenotypes, comparing in vitro versus in planta effects helps separate general growth defects from specific pathogenicity impacts.

What strategies can overcome the challenges of producing sufficient quantities of functional atpB for structural studies?

Structural studies require milligram quantities of pure, homogeneous protein, presenting particular challenges for membrane proteins like atpB. High-yield expression strategies include using strong promoters with tight regulation, optimizing codon usage for the expression host, and testing multiple bacterial strains specifically designed for membrane protein expression . Fusion tags beyond the standard His-tag, such as MBP or SUMO, can increase solubility and expression levels. Fermentation in bioreactors allows scaled-up production while maintaining optimal growth conditions. For extraction from membranes, screen multiple detergents systematically, considering factors like critical micelle concentration and micelle size. Detergent exchange during purification can improve protein stability; often, extraction requires stronger detergents while final buffers use milder ones. Alternative membrane mimetics like nanodiscs, amphipols, or SMALPs can enhance protein stability and homogeneity for structural studies. For crystallography, identify stabilizing additives through thermal shift assays and consider co-crystallization with binding partners or inhibitors. For cryo-EM, optimize grid preparation parameters including detergent concentration, buffer components, and vitrification conditions. Automated high-throughput screening of crystallization or sample preparation conditions can identify optimal parameters for structural studies.

How does atpB function compare between Pseudomonas syringae pathovars that infect different plant hosts?

Comparative analysis of atpB across Pseudomonas syringae pathovars can reveal adaptations related to host specificity. Sequence alignment of atpB from P. syringae pv. phaseolicola (bean pathogen) with pathovars like pv. tomato (tomato pathogen) or pv. syringae (broader host range) can identify pathovar-specific variations . Key areas to examine include transmembrane domains and residues involved in proton translocation. Researchers should investigate whether atpB expression patterns differ when various pathovars are exposed to their respective host plant extracts, using methods similar to the transcriptional profiling described for P. syringae pv. phaseolicola . Functional studies comparing ATP synthesis rates or proton translocation efficiency across pathovars can reveal biochemical adaptations. Cross-complementation experiments, expressing atpB from one pathovar in another, can test functional conservation. Structural models based on sequence variations may predict pathovar-specific features. Metabolomic studies measuring ATP levels in different pathovars during infection can connect atpB function to energy requirements for different host interactions. Evolutionary analysis of atpB sequences can identify positions under positive selection, potentially indicating host adaptation sites.

What insights can be gained from comparing the regulation of atpB gene expression across different bacterial pathogens?

Comparative analysis of atpB regulation across bacterial pathogens can reveal shared principles and pathogen-specific adaptations. Promoter sequence analysis comparing atpB upstream regions across Pseudomonas species and other plant pathogens can identify conserved regulatory elements. Transcriptomic data comparing atpB expression profiles during infection with various host plants can reveal host-specific regulatory patterns . Investigation of global regulators controlling atpB expression, such as sigma factors or two-component systems, across different pathogens can identify common regulatory networks. Analysis of atpB co-expression with virulence factors across different bacterial species can reveal potential coordination between energy metabolism and pathogenicity . Chromatin immunoprecipitation studies identifying transcription factors binding to the atpB promoter in different pathogens can provide direct evidence of regulatory mechanisms. Comparative analysis of stress response elements in atpB promoters can connect energy metabolism to stress adaptation across bacterial pathogens. Integration of transcriptional regulation data with post-transcriptional mechanisms like small RNAs can provide a comprehensive view of atpB expression control. These comparative approaches can identify both universal bacterial strategies and species-specific adaptations in ATP synthase regulation.