Recombinant Clavibacter michiganensis subsp. sepedonicus ATP synthase subunit b (atpF)

What is the genetic context of atpF in Clavibacter michiganensis subsp. sepedonicus?

The atpF gene in Clavibacter michiganensis subsp. sepedonicus encodes the ATP synthase subunit b, which is part of the F0 domain of ATP synthase. This gene is considered a conserved housekeeping gene, similar to other ATP synthase components like atpD (which encodes the ATP synthase β chain) . The atpF gene is chromosomally encoded and maintained as part of the core genome of Clavibacter michiganensis subspecies. Within the comparative genomic landscape of Clavibacter subspecies, Cms (C. michiganensis subsp. sepedonicus) shows distinctive genomic features including a high number of subspecies-specific coding sequences and numerous mobile elements . This suggests that while atpF is conserved as part of essential cellular machinery, the genetic context surrounding it may vary between subspecies.

To examine the genetic context of atpF:

• Extract genomic DNA using standard bacterial DNA isolation protocols

• Perform PCR amplification using primers designed from conserved flanking regions

• Sequence the amplified region to determine the genetic organization around atpF

• Compare the sequence with other Clavibacter subspecies to identify unique features

How can researchers express recombinant atpF protein for in vitro studies?

Expression of recombinant Clavibacter michiganensis subsp. sepedonicus ATP synthase subunit b requires:

• Gene amplification and cloning:

  • Design primers based on the Cms atpF sequence with appropriate restriction sites

  • Amplify the gene using high-fidelity PCR (typically 35 cycles: denaturation at 94°C for 30s, annealing at gene-specific temperature, extension at 72°C for 1 min)

  • Clone into an appropriate expression vector (pET systems are commonly used)

• Expression optimization:

  • Transform into E. coli expression strains (BL21(DE3) or derivatives)

  • Test expression at different temperatures (18°C, 25°C, 37°C)

  • Optimize IPTG concentration (0.1-1.0 mM) and induction time (3-16 hours)

  • Consider codon optimization if expression levels are low

• Protein purification:

  • Include an affinity tag (His6, GST) for simplified purification

  • Use immobilized metal affinity chromatography followed by size exclusion chromatography

  • Verify purity by SDS-PAGE and identity by Western blotting or mass spectrometry

Commercial sources like CUSABIO TECHNOLOGY LLC provide ready-to-use recombinant protein, which may be advantageous for researchers lacking expression facilities .

What analytical methods are suitable for characterizing purified atpF protein?

Characterization of purified recombinant ATP synthase subunit b should include:

• Structural analysis:

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

  • Thermal shift assays to determine protein stability

  • Dynamic light scattering (DLS) to evaluate oligomeric state and homogeneity

• Functional analysis:

  • ATPase activity assays using colorimetric phosphate detection

  • Reconstitution experiments with other ATP synthase subunits

  • Protein-protein interaction studies using pull-down assays or surface plasmon resonance

• Biophysical characterization:

  • Mass spectrometry for accurate molecular weight determination

  • N-terminal sequencing to confirm correct processing

  • Analytical ultracentrifugation for quaternary structure analysis

When interpreting results, consider that membrane proteins like ATP synthase subunits may require detergents or lipid environments for proper folding and function.

How is atpF utilized in multilocus sequence analysis (MLSA) of Clavibacter subspecies?

ATP synthase genes, including atpF and atpD, serve as valuable genetic markers in multilocus sequence-based analysis and typing (MLSA and MLST) of Clavibacter michiganensis subspecies. While atpD (encoding ATP synthase β chain) is commonly used in such analyses , the approach can be applied to atpF as well:

• Primer design and sequence amplification:

  • Design primers targeting conserved regions of atpF

  • Amplify the gene segment from multiple strains and subspecies

  • Sequence the PCR products using both forward and reverse primers

• Sequence alignment and analysis:

  • Align sequences using software like MUSCLE or CLUSTAL

  • Trim sequences to ensure equal length for analysis

  • Calculate sequence polymorphisms and genetic distances

• Phylogenetic tree construction:

  • Use Maximum Likelihood, Neighbor-Joining, or Bayesian inference methods

  • Assess tree reliability using bootstrap analysis (typically 1000 replicates)

  • Compare topologies with trees generated from other housekeeping genes

The MLSA approach using housekeeping genes like atpF provides robust phylogenetic resolution compared to 16S rRNA sequencing alone, which often lacks discriminatory power at the subspecies level .

How does atpF sequence variation correlate with pathogenicity in Clavibacter michiganensis subspecies?

The correlation between atpF sequence variation and pathogenicity in Clavibacter subspecies requires careful analysis:

• Comparative sequence analysis:

  • Obtain atpF sequences from pathogenic and non-pathogenic strains

  • Conduct detailed alignment and polymorphism identification

  • Calculate nucleotide diversity (π) and tests of selection (dN/dS ratios)

• Strain characterization:

  • Perform pathogenicity assays on appropriate host plants

  • Document disease symptoms and bacterial titers in planta

  • Correlate pathogenicity with specific sequence variations

• Functional impact assessment:

  • Model protein structure changes resulting from sequence variations

  • Express variants and assess functional differences in vitro

  • Perform complementation studies in mutant strains

What PCR-based detection methods can be developed using the atpF gene?

Development of PCR-based detection methods targeting atpF requires:

• Primer design strategy:

  • Analyze sequence alignments of atpF from multiple Clavibacter subspecies

  • Identify regions that are conserved within subspecies but variable between them

  • Design primers with optimal properties (Tm ~60°C, low self-complementarity)

  • Consider adding a probe for quantitative real-time PCR applications

• PCR optimization:

  • Determine optimal annealing temperature through gradient PCR

  • Optimize reaction components (MgCl₂ concentration, polymerase type)

  • Establish detection limits using serially diluted template

  • Test primers against a panel of non-target organisms to confirm specificity

• Validation protocol:

  • Test with a diverse collection of target and non-target bacteria

  • Include field samples to assess performance with complex matrices

  • Compare results with established detection methods for the pathogen

A typical PCR protocol would involve initial denaturation at 94°C for 5 min, followed by 35 cycles of denaturation at 94°C for 30s, annealing at the gene-specific temperature, and extension at 72°C for 1 min, with a final extension at 72°C for 10 min .

How can LAMP assays be developed for detecting atpF in field samples?

Loop-mediated isothermal amplification (LAMP) offers advantages for field detection of Clavibacter michiganensis:

• LAMP primer design:

  • Design six primers (F3, B3, FIP, BIP, LF, LB) targeting distinct regions of atpF

  • Ensure primers have appropriate melting temperatures (55-65°C)

  • Check for self-complementarity and primer-dimer formation

  • Validate in silico against sequence databases

• Reaction optimization:

  • Test different DNA polymerases (Bst 2.0 is commonly used)

  • Optimize reaction temperature (typically 60-65°C)

  • Determine optimal reaction time (usually 30-60 minutes)

  • Incorporate colorimetric detection methods (pH indicators, fluorescent dyes)

• Field application protocol:

  • Develop simplified sample preparation methods

  • Create positive and negative controls for field use

  • Establish result interpretation guidelines

  • Validate using blind testing of field samples

Studies on Clavibacter michiganensis have successfully used LAMP assays for detection in seed samples , and similar approaches could be adapted for atpF-based detection of Clavibacter michiganensis subsp. sepedonicus.

How can protein-protein interactions of ATP synthase subunit b be studied?

Investigating protein-protein interactions of ATP synthase subunit b requires multiple complementary approaches:

• In vitro interaction studies:

  • Pull-down assays using tagged recombinant proteins

  • Surface plasmon resonance (SPR) for binding kinetics

  • Isothermal titration calorimetry (ITC) for thermodynamic parameters

  • Chemical cross-linking followed by mass spectrometry

• In vivo interaction analysis:

  • Bacterial two-hybrid assays

  • Förster resonance energy transfer (FRET) with fluorescently tagged proteins

  • Co-immunoprecipitation from bacterial lysates

  • Split-GFP complementation assays

• Structural characterization:

  • X-ray crystallography of protein complexes

  • Cryo-electron microscopy for larger assemblies

  • NMR spectroscopy for mapping interaction interfaces

  • Hydrogen-deuterium exchange mass spectrometry

ATP synthase subunit b typically interacts with other components of the F₀ complex and serves as a peripheral stalk connecting F₁ and F₀ domains. Understanding these interactions is crucial for elucidating the structure-function relationship of the complete ATP synthase complex.

What are the challenges in structural studies of recombinant ATP synthase subunit b?

Structural studies of ATP synthase subunit b face several challenges:

• Protein expression and purification obstacles:

  • Membrane-associated proteins are often difficult to express

  • Protein may aggregate without proper membrane mimetics

  • Detergent selection is critical for maintaining native structure

  • Purification yields may be low due to toxicity or inclusion body formation

• Crystallization challenges:

  • Intrinsic flexibility in certain regions complicates crystal formation

  • Finding optimal crystallization conditions requires extensive screening

  • Co-crystallization with stabilizing partners may be necessary

  • Membrane proteins typically have lower crystallization success rates

• Alternative structural approaches:

  • Cryo-electron microscopy for single-particle analysis

  • Solid-state NMR for membrane-embedded proteins

  • Small-angle X-ray scattering (SAXS) for low-resolution envelope

  • Computational modeling based on homologous structures

To overcome these challenges, researchers often employ strategies such as truncation constructs, fusion with crystallization chaperones, or incorporation into nanodiscs or amphipols.

How can genome editing techniques be applied to study atpF function in Clavibacter michiganensis?

Genome editing of atpF in Clavibacter michiganensis requires:

• CRISPR-Cas9 based approach:

  • Design sgRNAs targeting specific regions of atpF

  • Create a delivery vector compatible with Clavibacter

  • Include appropriate homology arms for repair template

  • Optimize transformation protocol for high efficiency

• Homologous recombination strategy:

  • Design constructs with selection markers flanked by homologous regions

  • Transform cells using electroporation or conjugation

  • Screen transformants using antibiotic selection

  • Verify mutations by PCR and sequencing

• Phenotypic characterization:

  • Assess growth rates in different media and conditions

  • Measure ATP synthesis capacity

  • Evaluate membrane potential maintenance

  • Test pathogenicity in appropriate plant hosts

• Complementation analysis:

  • Reintroduce wild-type or mutant atpF variants

  • Use inducible promoters for controlled expression

  • Assess restoration of phenotypes

  • Quantify expression levels by RT-qPCR

Genetic manipulation in Clavibacter is challenging due to its Gram-positive nature and limited genetic tools, but recent advances in bacterial genome editing have made targeted mutations increasingly feasible.

How does atpF sequence conservation compare across Clavibacter subspecies?

Analysis of atpF sequence conservation across Clavibacter subspecies reveals:

Comparative genomics studies have shown that while Clavibacter michiganensis subspecies share a core genome, Cms (C. michiganensis subsp. sepedonicus) displays the highest number of subspecies-specific coding sequences . This suggests unique evolutionary pressures on this subspecies that may also influence the evolution of housekeeping genes like atpF.

What insights can atpF sequence analysis provide about the evolution of Clavibacter subspecies?

Evolutionary analysis of atpF sequences can provide valuable insights:

• Molecular clock analysis:

  • Calculate substitution rates in atpF compared to other genes

  • Estimate divergence times between subspecies

  • Identify periods of rapid or constrained evolution

  • Correlate with known historical events in bacterial evolution

• Selection pressure assessment:

  • Calculate dN/dS ratios to identify purifying or positive selection

  • Perform codon-based tests of selection

  • Identify specific amino acid sites under selection

  • Compare selection patterns with other ATP synthase subunits

• Recombination analysis:

  • Test for evidence of horizontal gene transfer

  • Identify potential recombination breakpoints

  • Assess impact of recombination on phylogenetic inference

  • Compare with recombination patterns in other genomic regions

Analysis of housekeeping genes in Clavibacter michiganensis has shown that the subspecies form distinct phylogenetic groups . Recent studies suggest that some Clavibacter subspecies may warrant elevation to species level based on genome-wide DNA homology , and atpF sequence analysis could contribute additional evidence for taxonomic reclassification.

What bioinformatic pipelines are recommended for analyzing atpF sequence data?

A comprehensive bioinformatic pipeline for atpF analysis should include:

• Sequence quality assessment and preprocessing:

  • Trim low-quality bases (typically Phred score <20)

  • Remove adapter sequences and primers

  • Merge overlapping paired-end reads if applicable

  • Filter sequences by length and quality metrics

• Comparative sequence analysis:

  • Multiple sequence alignment (MUSCLE, MAFFT, or ClustalW)

  • Alignment visualization and editing (Jalview, MEGA)

  • Conservation analysis (ConSurf, WebLogo)

  • Polymorphism identification and annotation

• Phylogenetic analysis:

  • Model testing to identify optimal evolutionary models

  • Tree construction using Maximum Likelihood or Bayesian methods

  • Bootstrap analysis (minimum 1000 replicates)

  • Tree visualization and annotation (FigTree, iTOL)

• Functional prediction:

  • Protein structure prediction (Alphafold2, I-TASSER)

  • Functional domain annotation (InterProScan, CDD)

  • Impact prediction for amino acid substitutions (PROVEAN, SIFT)

  • Protein-protein interaction prediction (STRING)

For multilocus sequence analysis incorporating atpF with other genes, concatenated alignments can be created after individual gene analysis, as demonstrated in studies of Clavibacter michiganensis using six housekeeping genes .

How can researchers integrate atpF data with other genomic information for comprehensive analysis?

Integration of atpF data with other genomic information requires:

Genome comparison across Clavibacter subspecies has revealed significant variations in genome size, gene content, and mobile elements . Integration of atpF data with these genome-wide analyses can provide a more comprehensive understanding of the evolutionary relationships and functional adaptations among Clavibacter subspecies.