Recombinant Acinetobacter baumannii ATP synthase subunit b (atpF)

What is the subunit composition of the A. baumannii F1FO-ATP synthase?

The complete A. baumannii F1FO-ATP synthase (AbF1FO) has a subunit composition of α3:β3:γ:δ:ε:a:b2:c10. This multisubunit complex consists of a membrane-embedded FO sector and a soluble F1 catalytic sector. The F1 sector primarily contains subunits α3:β3:γ:ε, which are responsible for ATP synthesis and hydrolysis. The FO sector, which includes subunit b (present as a dimer, b2), forms the proton channel across the membrane .

What is known about the catalytic properties of A. baumannii ATP synthase?

A. baumannii F1FO-ATP synthase shows latent ATPase activity, meaning it is incapable of ATP-driven proton translocation. This is a critical adaptation for this strictly respiratory opportunistic human pathogen. Experimental evidence demonstrates that the recombinant A. baumannii F1-ATPase (AbF1-ATPase) composed of subunits α3:β3:γ:ε exhibits this latent ATP hydrolysis. When the ε subunit is removed (creating an ε-free AbF1-αβγ complex), ATP hydrolysis increases by 21.5-fold, indicating that subunit ε is the major regulator of the latent ATPase activity .

What structural information is available for A. baumannii ATP synthase?

Multiple high-resolution structures of A. baumannii ATP synthase components have been determined. These include:

These structures have provided valuable insights into both the nucleotide-converting F1 subcomplex and the membrane-embedded FO complex.

What expression systems have been successful for producing recombinant A. baumannii ATP synthase components?

Based on current research, heterologous expression systems have been employed successfully for A. baumannii ATP synthase components. While the search results don't specifically mention the expression system for subunit b, they describe the procedure for other components which can serve as a methodological template. Researchers have used both homologous expression (within A. baumannii) and heterologous systems for various subunits .

For expression in A. baumannii, the following methodology has been employed:

• Construction of expression vectors using pBBR-MCS3 plasmid

• Introduction of confirmed sequence plasmids (like pBBR_AbATPbetaSII) into A. baumannii cells via electroporation

• Growth of transformed cells in TB media containing appropriate antibiotics (e.g., tetracycline at 15 μg/ml)

What is the recommended purification protocol for recombinant A. baumannii ATP synthase components?

The purification of A. baumannii ATP synthase components typically involves a multi-step process:

• Cell lysis: Cells are disrupted using French pressure cell at 20,000 psi followed by centrifugation at 10,000 g for 1 hour

• Membrane preparation: Supernatant is filtered and centrifuged at 200,000 g for 1 hour to harvest membranes

• Solubilization: Membranes are solubilized in buffer containing appropriate detergents (e.g., 1% w/v tPCC-α-M)

• Affinity chromatography: Solubilized protein is purified using Strep affinity column

• Ion exchange chromatography: Further purification using MonoQ 5/50 GL column with gradual elution using KCl

• Final polishing: Additional steps may include desalting and binding to Q Sepharose material

• Reconstitution: The purified protein can be reconstituted into peptidiscs or other suitable membrane mimetics

This protocol has been successful for other ATP synthase components and could be adapted for subunit b with appropriate affinity tags.

What methods have been effective for structural characterization of A. baumannii ATP synthase components?

Multiple complementary techniques have been employed to elucidate the structure of A. baumannii ATP synthase components:

For subunit b specifically, a combination of these approaches would likely be effective, with particular emphasis on its interactions within the larger complex.

How can one assess the functional activity of recombinant A. baumannii ATP synthase components?

Functional assessment of ATP synthase components typically involves several complementary approaches:

• ATP hydrolysis assays: Measuring ATPase activity to quantify the rate of ATP hydrolysis. This can be done with purified components or reconstituted complexes.

• ATP synthesis measurements: Using inverted membrane vesicles containing ATP synthase complexes to assess ATP synthesis capacity under appropriate conditions.

• Mutational analysis: Generating single amino acid substitutions or truncation mutants to identify residues critical for function. For example, the importance of subunit ε's C-terminus in ATP synthesis has been explored using a heterologous expression system .

• Interaction studies: Assessing the binding interactions between different subunits and their impact on enzymatic activity.

These approaches have been successfully applied to other A. baumannii ATP synthase components and could be adapted for studies of subunit b.

How does subunit b contribute to the stability and assembly of the A. baumannii ATP synthase complex?

While the search results don't specifically address this for subunit b, related research approaches could include:

Such approaches would help elucidate the role of subunit b in the structural integrity of the ATP synthase complex.

What are the unique structural adaptations in A. baumannii ATP synthase compared to other bacterial and mitochondrial ATP synthases?

The A. baumannii F1FO-ATP synthase exhibits several unique structural features:

• In the membrane-embedded FO complex, there are specific structural adaptations along both the entry and exit pathways of the proton-conducting a-subunit. These features are absent in mitochondrial ATP synthases .

• The F1 subcomplex reveals a specific self-inhibition mechanism that supports a unidirectional ratchet mechanism to avoid wasteful ATP consumption .

• Unlike some bacterial counterparts, the A. baumannii subunit ε (Abε) does not bind MgATP, which in other bacteria regulates the up and down movements of this subunit .

These unique structural features represent potential targets for the development of selective therapeutics against this pathogen.

How can site-directed mutagenesis be used to probe the function of specific residues in ATP synthase subunit b?

Site-directed mutagenesis approaches, as applied to other A. baumannii ATP synthase components, provide a template for subunit b studies:

• Identification of conserved or potentially important residues through sequence alignment and structural analysis

• Generation of single amino acid substitutions or truncation mutants using PCR-based mutagenesis techniques

• Expression and purification of mutant proteins using established protocols

• Functional characterization through:

  • Assembly studies to assess the impact on complex formation

  • Activity assays to measure effects on ATP synthesis and hydrolysis

  • Stability assessments to determine effects on complex integrity

• Structural studies of mutant proteins to visualize conformational changes

This approach has been successfully employed for subunit ε, where both single amino acid substitutions and C-terminal truncated mutants were created to identify elements critical for the self-inhibition mechanism of ATP hydrolysis .

Why is the A. baumannii ATP synthase considered a potential drug target?

The A. baumannii ATP synthase represents an attractive therapeutic target for several reasons:

• Essential function: The ATP synthase is essential for this strictly respiratory opportunistic human pathogen's survival.

• Unique features: The complex contains structural adaptations not present in human mitochondrial ATP synthases, potentially allowing for selective targeting.

• Multidrug resistance: A. baumannii is part of the ESKAPE group of pathogens known for antimicrobial resistance, necessitating novel therapeutic approaches .

• Bioenergetic bottleneck: Targeting ATP synthase affects the culmination of bioenergetics in this pathogen, potentially disrupting multiple cellular processes simultaneously.

These factors make the ATP synthase, including subunit b, a promising target for next-generation therapeutics against this clinically relevant pathogen.

What experimental approaches can be used to identify potential inhibitors targeting specific subunits of A. baumannii ATP synthase?

Several experimental approaches could be employed to identify inhibitors targeting ATP synthase subunits:

• Structure-based drug design: Using the available structural information to design compounds that bind to specific sites, particularly those unique to A. baumannii.

• High-throughput screening: Testing libraries of compounds against purified ATP synthase components or reconstituted complexes.

• Fragment-based drug discovery: Identifying small molecular fragments that bind to subunits and can be developed into larger, more potent inhibitors.

• ATP hydrolysis inhibition assays: Screening compounds for their ability to inhibit the ATPase activity of purified complexes.

• Growth inhibition assays: Testing compounds for their ability to selectively inhibit growth of A. baumannii compared to human cells.

These approaches could be specifically tailored to target subunit b or its interactions within the larger ATP synthase complex.

What are the major challenges in expressing and purifying functional recombinant A. baumannii ATP synthase subunit b?

While the search results don't specifically address challenges for subunit b, the following challenges are commonly encountered with ATP synthase components and can be anticipated:

• Protein solubility: Membrane proteins like subunit b often have solubility issues. This can be addressed through:

  • Optimization of detergent type and concentration

  • Use of fusion partners to enhance solubility

  • Exploration of membrane mimetics like nanodiscs or peptidiscs

• Maintaining native conformation: Ensuring the recombinant protein maintains its functional fold, especially if expressed in heterologous systems.

• Protein-protein interactions: Subunit b normally exists in a complex, and isolation may affect stability.

• Functional assessment: Developing appropriate assays to verify that the recombinant protein maintains native functionality.

How can protein engineering be used to enhance the stability or expression of A. baumannii ATP synthase components?

Several protein engineering strategies could be employed:

• Introduction of stabilizing mutations based on comparative sequence analysis or computational prediction.

• Design of fusion constructs with solubility-enhancing partners that can be later removed if necessary.

• Codon optimization for the expression host to improve translation efficiency.

• Introduction of affinity tags at locations that minimize interference with function and structure.

• Co-expression with chaperones or partner proteins that facilitate proper folding and assembly.

These approaches have proven successful for other challenging membrane proteins and could be applied to A. baumannii ATP synthase subunit b.