Recombinant Shigella dysenteriae serotype 1 ATP synthase subunit a (atpB)

What is the structure and function of Shigella dysenteriae serotype 1 ATP synthase subunit a (atpB)?

ATP synthase subunit a (atpB) from Shigella dysenteriae serotype 1 is a critical component of the F0 sector of ATP synthase, a multi-subunit enzyme complex responsible for ATP production. The protein consists of 271 amino acids with a predominantly hydrophobic profile, reflecting its membrane-embedded position . The protein functions as part of the proton channel within the F0 sector, facilitating the translocation of protons across the membrane that ultimately drives ATP synthesis.

The amino acid sequence (MASENMTPQDYIGHHLNNLQLDLRTFSLVDPQNPPATFWTINIDSMFFSVGLGLLFLVLFRSVAKKATSGVPGKFQTAIELVIGFVNGSVKDMYHGKSKLIAPLALTIFVWVFLMNLMDLLPIDLLPYIAEHVLGLPALRVVPSADVNVTLSMALGVFILILFYSIKMKGIGGFTKELTLQPFNHWAFIPVNLILEGVSLLSKPVSLGLRLFGNMYAGELIFILIAGLLPWWSQWILNVPWAIFHILIITLQAFIFMVLTIVYLSMASEEH) reveals multiple transmembrane domains that anchor the protein within the bacterial membrane .

How does recombinant Shigella dysenteriae atpB differ from native protein?

The recombinant Shigella dysenteriae serotype 1 ATP synthase subunit a protein is expressed with an N-terminal His-tag to facilitate purification . While the core protein structure remains intact, the addition of this tag creates several important distinctions from the native protein:

• Molecular weight differences due to the addition of histidine residues

• Potential changes in solubility characteristics

• Modified isoelectric point

• Availability of a metal affinity purification method

What are the optimal storage conditions for recombinant Shigella dysenteriae atpB protein?

The recombinant atpB protein requires specific storage conditions to maintain stability and activity:

Repeated freeze-thaw cycles should be avoided as they can lead to protein denaturation and loss of activity . The presence of trehalose in the buffer serves as a cryoprotectant, helping to maintain protein structure during the freeze-thaw process.

What are the recommended approaches for reconstituting lyophilized atpB protein?

For optimal reconstitution of lyophilized Shigella dysenteriae atpB protein:

• Briefly centrifuge the vial prior to opening to ensure all contents settle at the bottom

• Reconstitute in deionized sterile water to achieve a concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 5-50% (with 50% being the standard recommendation) for long-term storage

• Aliquot the reconstituted protein to minimize freeze-thaw cycles

• Verify protein concentration using spectrophotometric methods after reconstitution

This methodological approach ensures maximum retention of protein functionality while minimizing degradation. The addition of glycerol helps prevent ice crystal formation during freezing, which could otherwise damage protein structure.

How can researchers verify the purity and integrity of recombinant atpB protein?

Multiple complementary analytical techniques should be employed to assess protein purity and integrity:

• SDS-PAGE analysis: The recombinant protein should demonstrate >90% purity by SDS-PAGE . A single dominant band at the expected molecular weight (approximately 30 kDa plus His-tag) confirms identity and purity.

• Western blotting: Using anti-His antibodies can confirm the presence of the recombinant protein.

• Mass spectrometry: For precise molecular weight determination and verification of sequence integrity.

• Dynamic light scattering (DLS): To assess protein homogeneity and detect potential aggregation.

• Circular dichroism (CD): To analyze secondary structure and confirm proper folding.

The combined results from these techniques provide comprehensive quality assessment of the recombinant protein before experimental use.

How does atpB structure and function compare to T3SS ATPases like Spa47 in Shigella species?

While both atpB and Spa47 are ATP-interacting proteins in Shigella species, they have distinct structural and functional roles:

Spa47 forms oligomeric structures that are critical for its ATP hydrolysis activity, with oligomeric forms showing approximately 8-fold higher activity than monomeric forms . This oligomerization-dependent activation represents a potential regulatory mechanism for T3SS function. In contrast, atpB functions as part of the proton channel in the membrane-embedded F0 sector of ATP synthase .

Structural studies of Spa47 have revealed that ATP binding induces conformational changes that spread from the binding pocket to the conserved luminal loop facing the predicted pore of the Spa47 hexamer . These findings suggest mechanistic similarities between T3SS ATPases and F/V-type ATPases, potentially indicating a common evolutionary origin .

What methodological approaches can be used to study atpB oligomerization and protein-protein interactions?

To investigate atpB oligomerization and protein-protein interactions:

• Size exclusion chromatography (SEC): Separate different oligomeric states based on molecular size.

• Analytical ultracentrifugation (AUC): Determine the sedimentation coefficient and molecular weight of different protein species in solution, as has been effectively used with Spa47 .

• Blue native PAGE: Separate native protein complexes while maintaining protein-protein interactions.

• Cross-linking coupled with mass spectrometry: Identify interaction interfaces and protein complex topology.

• Förster resonance energy transfer (FRET): Measure protein-protein interactions in real-time.

• Surface plasmon resonance (SPR): Determine binding kinetics and affinity constants.

• Isothermal titration calorimetry (ITC): Measure thermodynamic parameters of protein interactions.

Research on Spa47 has demonstrated that oligomerization significantly impacts ATPase activity, with oligomeric forms showing much higher activity than monomeric forms . Similar methodologies could be applied to investigate whether atpB activity is also influenced by its incorporation into larger protein complexes.

How can researchers investigate the role of atpB in Shigella virulence and pathogenesis?

Investigating the role of atpB in Shigella virulence requires a multi-faceted approach:

• Gene knockout and complementation studies: Create atpB deletion mutants and complement with wild-type or mutant atpB to assess the impact on bacterial growth and virulence.

• Site-directed mutagenesis: Target conserved residues to identify those critical for function, similar to approaches used with Spa47's catalytic Walker A domain .

• Invasion assays: Determine if atpB mutations impact the ability of Shigella to invade host cells.

• Cellular ATP measurement: Quantify ATP production in wild-type versus atpB mutant strains.

• In vivo infection models: Assess the virulence of atpB mutants in appropriate animal models.

What are the key catalytic residues in Shigella dysenteriae atpB and how do they compare to other ATP-related proteins?

The catalytic mechanism of ATP synthase involves several conserved residues in the atpB subunit that facilitate proton translocation. In Shigella dysenteriae serotype 1 atpB, key functional regions include:

• Transmembrane helices: The protein contains multiple hydrophobic segments that form transmembrane helices, creating a proton channel through the membrane.

• Conserved charged residues: Specific charged amino acids within the transmembrane regions likely participate in proton translocation.

In comparison, the T3SS ATPase Spa47 from Shigella flexneri contains well-defined motifs for ATP binding and hydrolysis:

• Walker A motif: Contains a conserved lysine residue essential for ATP binding. Mutation of this lysine residue (K165A) abolishes ATPase activity .

• Arginine finger: The conserved R350 residue is critical for ATP hydrolysis, though it does not directly contribute to ATP binding .

Understanding these structural elements provides insight into the distinct but related mechanisms by which different ATP-interacting proteins function in Shigella species.

How do mutations in atpB affect ATP synthase function and bacterial physiology?

Studies on the related T3SS ATPase Spa47 have shown that mutations in catalytic residues can abolish ATPase activity while maintaining oligomerization capacity . These findings suggest that protein-protein interactions and enzymatic activity can be uncoupled, at least in some ATP-related proteins in Shigella.

Similar methodological approaches could be applied to atpB, using site-directed mutagenesis to target conserved residues followed by functional assays to assess the impact on ATP synthesis and bacterial growth.

How does Shigella dysenteriae atpB compare to homologous proteins in other bacterial species?

ATP synthase subunit a is highly conserved across bacterial species, reflecting its essential role in energy metabolism. Comparative analysis reveals:

• Sequence conservation: High sequence similarity, particularly in functional domains involved in proton translocation.

• Structural homology: Conserved transmembrane topology across species.

• Functional conservation: Similar role in the ATP synthase complex across different bacterial taxa.

What is the relationship between ATP synthase and type III secretion system ATPases in Shigella species?

Research on Shigella ATPases suggests evolutionary and mechanistic connections between different ATP-utilizing systems:

• Shared architectural features: Both ATP synthase and T3SS contain ring-shaped ATPase complexes .

• Mechanistic similarities: Studies on Spa47 indicate that nucleotide-driven conformational changes may be linked to rotation mechanisms similar to those in F/V-type ATPases .

• Evolutionary relationship: The structural similarities suggest a potential common evolutionary origin between T3SS ATPases and F/V-type ATPases .

These connections provide a broader perspective on the evolution of energy-coupling systems in bacteria and highlight the diverse ways in which ATP-interacting proteins have been adapted for different cellular functions, from energy production to virulence.

What are the major challenges in working with membrane proteins like atpB and how can they be addressed?

Working with membrane proteins presents several technical challenges:

• Solubilization: Membrane proteins like atpB require detergents or other solubilizing agents for extraction from membranes.
  Solution: Optimize detergent type and concentration; consider using amphipols or nanodiscs for stabilization.

• Maintaining native conformation: Detergent-solubilized proteins may not retain native structure.
  Solution: Use mild detergents and validate protein folding with spectroscopic methods.

• Functional assays: Testing activity outside the membrane environment is challenging.
  Solution: Reconstitute into proteoliposomes for functional studies; develop membrane-mimetic systems.

• Crystallization: Membrane proteins are notoriously difficult to crystallize.
  Solution: Consider lipidic cubic phase crystallization; explore alternative structural biology approaches like cryo-EM.

These methodological considerations are essential for successful experimental work with membrane-embedded proteins like atpB.

What are the promising research areas for Shigella dysenteriae atpB in relation to antimicrobial development?

As drug resistance becomes increasingly prevalent in Shigella species , exploring atpB as a potential antimicrobial target offers several research opportunities:

• Structure-based drug design: Using the structural information of atpB to design specific inhibitors that disrupt ATP synthesis.

• Combination therapies: Investigating synergistic effects between ATP synthase inhibitors and existing antibiotics.

• Comparative analyses: Exploring structural and functional differences between bacterial and human ATP synthases to develop selective inhibitors.

• Alternative approaches: Investigating the potential of atpB-targeting aptamers, peptides, or antibodies as novel therapeutic modalities.

With extensively drug-resistant (XDR) Shigella infections emerging as a significant public health concern , innovative approaches targeting essential metabolic machinery like ATP synthase represent an important avenue for future antimicrobial development.