Recombinant Mycoplasma hyopneumoniae ATP synthase subunit c (atpE)

Basic Research Questions

• What is the structure and function of ATP synthase subunit c (atpE) in Mycoplasma hyopneumoniae?

  ATP synthase subunit c (atpE) in Mycoplasma hyopneumoniae is a key component of the F(0) channel that plays a direct role in translocation across the bacterial membrane. The protein forms a homomeric c-ring consisting of 10-14 subunits that, together with the F(1) delta and epsilon subunits, constitutes the central stalk rotor element of the ATP synthase complex. This molecular machine is essential for energy production in the bacterium.

  The Mycoplasma hyopneumoniae atpE protein:

  • Contains 101 amino acids

  • Has a molecular mass of approximately 10.5 kDa

  • Belongs to the ATPase C chain family

  • Contains highly hydrophobic regions allowing membrane integration

  • Has the amino acid sequence: MNSIVNFSQQLIQNFQEVSQRTAADSSNLKAFAYLGAGLAMIGVIGVGAGQGYAAGKACDAIARNPEAQKQVFRVLVIGTAISETSSIYALLVALILIFVG

• How do recombinant expression systems for M. hyopneumoniae atpE differ from those used for other ATP synthase components?

  Recombinant expression of M. hyopneumoniae atpE presents unique challenges compared to other ATP synthase components like AtpD (β-subunit) due to its highly hydrophobic nature and membrane integration properties.

  When expressing atpE recombinantly:

  • E. coli is commonly used as an expression host, as seen with other ATP synthase components

  • N-terminal His-tagging is frequently employed for purification purposes, though tag placement must be carefully considered to prevent interference with protein folding and function

  • Expression often requires optimization of temperature, induction conditions, and solubilization methods

  • The integrity of epitopes may be affected by production methods, especially if glycosylation is required for antibody recognition

  • Unlike the larger, soluble AtpD subunit (approximately 52.5 kDa), the smaller (10.5 kDa) and highly hydrophobic atpE may require specialized solubilization and purification protocols

• What methodologies are most effective for purifying recombinant M. hyopneumoniae atpE while maintaining its native structure?

  Purification of recombinant M. hyopneumoniae atpE requires specialized techniques due to its hydrophobic nature and membrane protein characteristics:

  Effective purification protocol:

  1. Affinity chromatography using His-tag (if incorporated into the recombinant construct)

  2. Ion exchange chromatography for further purification

  3. Careful selection of detergents for solubilization (mild non-ionic detergents are preferred)

  4. Storage in specialized buffers containing glycerol to maintain stability

  For optimal storage conditions:

  • Store at -20°C/-80°C upon receipt

  • Aliquot to prevent repeated freeze-thaw cycles

  • Use Tris/PBS-based buffer with 6% Trehalose at pH 8.0 for storage

  • Add 5-50% glycerol (final concentration) when storing for long periods

  For reconstitution:

  • Reconstitute in deionized sterile water to 0.1-1.0 mg/mL

  • Centrifuge vials briefly before opening to bring contents to the bottom

• How does the amino acid sequence of M. hyopneumoniae atpE compare with atpE from other bacterial species?

  The M. hyopneumoniae atpE protein shares structural and functional similarities with other bacterial ATP synthase subunit c proteins, though with specific sequence variations:

  Comparison with Nocardioides sp. atpE:

  • M. hyopneumoniae atpE: 101 amino acids
    Sequence: MNSIVNFSQQLIQNFQEVSQRTAADSSNLKAFAYLGAGLAMIGVIGVGAGQGYAAGKACDAIARNPEAQKQVFRVLVIGTAISETSSIYALLVALILIFVG

  • Nocardioides sp. atpE: 69 amino acids
    Sequence: MAIEGSANMIGYGLAAIGPGVGIGLIFAAYISGVARQPEAQSRLQAIAILGFALAEALAIIGIALAFVL

  Key observations:

  • Both share hydrophobic regions critical for membrane integration

  • Both contain conserved residues involved in proton translocation

  • The M. hyopneumoniae sequence is longer, containing additional N-terminal regions

  • Despite differences, functional domains related to ring formation and proton channeling are conserved

  • Both proteins belong to the ATPase C chain family, reflecting their common evolutionary origin and function

Intermediate Research Questions

• What are the experimental challenges in verifying the functional activity of recombinant M. hyopneumoniae atpE?

  Verification of functional activity for recombinant M. hyopneumoniae atpE presents several experimental challenges:

  Major challenges:

  1. Proper oligomerization assessment: The protein must form a proper c-ring of 10-14 subunits to be functional

  2. Membrane integration: As a hydrophobic membrane protein, proper insertion into artificial membranes is required for activity testing

  3. Complex association: The c-subunit functions as part of the larger ATP synthase complex, making isolated functional assessment difficult

  Methodological approaches:

  • Proton translocation assays: Using fluorescent pH indicators to measure proton movement across reconstituted membranes

  • ATPase activity coupling: Measuring ATP hydrolysis/synthesis when combined with purified F1 components

  • Structural verification: Using circular dichroism spectroscopy to confirm secondary structure

  • Oligomerization assessment: Using size exclusion chromatography or native PAGE to verify proper assembly

  • Binding studies: Testing interaction with known binding partners from the ATP synthase complex

  Alternative validation approaches may include competitive binding assays with antibodies that recognize specific conformational epitopes of the native protein.

• How can recombinant M. hyopneumoniae atpE be used in the development of serological assays for disease diagnosis?

  Recombinant M. hyopneumoniae atpE shows potential as a diagnostic antigen for serological assays, similar to how the ATP synthase beta subunit (AtpD) has been used for M. pneumoniae diagnosis:

  Implementation approach:

  1. Antigen preparation:

     • Express recombinant atpE in E. coli with appropriate tags

     • Purify using affinity chromatography followed by ion exchange chromatography

     • Verify protein integrity through SDS-PAGE and western blotting

  2. ELISA development:

     • Coat microtiter plates with purified recombinant atpE

     • Block non-specific binding sites

     • Add diluted test samples (serum)

     • Detect using enzyme-labeled anti-pig antibodies

     • Develop with appropriate substrate and measure absorbance

  3. Performance assessment:

     • Determine cut-off values using ROC analysis

     • Calculate sensitivity and specificity

     • Compare with commercial assays

  Based on studies with similar ATP synthase components, optimal ELISA protocols for M. hyopneumoniae atpE might include:

  • Sample dilution at 1:5 ratio using appropriate diluent

  • Addition of detection solution (90 μL) to each well

  • Addition of 10 μL diluted samples

  • Incubation at 20-25°C for 30 minutes

  • Washing five times with wash buffer

  • Addition of enzyme-labeled antibody

  • Final detection with TMB substrate

  Validation would require testing against a panel of serum samples from infected and healthy animals to establish sensitivity and specificity parameters.

• What protein-protein interactions does M. hyopneumoniae atpE form within the ATP synthase complex and how can these be studied?

  M. hyopneumoniae atpE forms critical protein-protein interactions within the ATP synthase complex that are essential for its function:

  Key interactions:

  1. Self-association to form the c-ring oligomer (10-14 subunits)

  2. Interaction with subunit a of the F₀ sector at the a/c interface

  3. Interaction with the γ and ε subunits of the F₁ sector

  4. Possible interaction with regulatory proteins specific to Mycoplasma

  Methodological approaches to study these interactions:

  1. Co-immunoprecipitation (Co-IP):

     • Express tagged versions of atpE and potential interaction partners

     • Use antibodies to pull down the primary protein and identify binding partners by western blot or mass spectrometry

  2. Yeast two-hybrid (Y2H) screening:

     • Create fusion constructs of atpE with DNA-binding domains

     • Screen against Mycoplasma proteome fragments fused to activation domains

     • Identify interactions through reporter gene activation

  3. Surface plasmon resonance (SPR):

     • Immobilize purified atpE on sensor chips

     • Flow potential binding partners over the surface

     • Measure binding kinetics through changes in refractive index

  4. Crosslinking studies:

     • Use chemical crosslinkers to stabilize transient interactions

     • Analyze crosslinked products by SDS-PAGE and mass spectrometry

  5. Cryo-electron microscopy:

     • Visualize the entire ATP synthase complex

     • Map the location and interactions of the c-ring within the complex

     • Compare structures under different conditions or with mutations

  These methods can reveal both structural and functional aspects of atpE interactions that may be relevant to understanding M. hyopneumoniae energy metabolism and potential drug targets.

• How do the immunogenic properties of recombinant M. hyopneumoniae atpE compare with other M. hyopneumoniae proteins used in diagnostics?

  When comparing the immunogenic properties of recombinant M. hyopneumoniae atpE with other diagnostic antigens, several factors must be considered:

  Comparative immunogenicity analysis:

  1. Antibody response kinetics:

     • Similar to ATP synthase beta subunit (AtpD) in M. pneumoniae, atpE may induce antibody responses in early infection stages

     • Based on data from ATP synthase subunits, IgM antibodies may appear first (around 14 days post-infection), followed by IgA and IgG

  2. Antibody class distribution:

     • Studies with similar proteins show varying patterns of antibody class responses

     • For example, with AtpD in M. pneumoniae, 70% of children showed IgM positivity, 56% showed IgA positivity, and 78% showed IgG positivity

     • Adult serum samples showed 67% IgM positivity, 65% IgA positivity, and 61% IgG positivity against recombinant AtpD

  3. Sensitivity and specificity comparison:

     • ATP synthase components typically show high specificity (90-97%) in ELISA tests

     • When combined with other antigens like adhesins, diagnostic sensitivity can be improved

     • ROC analysis can determine optimal cut-off values for different antibody classes

  4. Antigen stability:

     • ATP synthase components are generally more conserved than surface variable proteins

     • This may provide more consistent diagnostic results across different M. hyopneumoniae strains

  5. Mucosal vs. systemic responses:

     • ATP synthase components may induce both mucosal (SIgA) and systemic (IgG) antibody responses

     • Data from vaccination studies show that SIgA antibody responses peak around 14 days post-immunization

  These comparisons suggest that recombinant atpE could potentially serve as a valuable diagnostic antigen, particularly when used in combination with other M. hyopneumoniae proteins to improve sensitivity and specificity.