Recombinant Actinobacillus succinogenes ATP synthase subunit a (atpB)

What is ATP synthase subunit a (atpB) in Actinobacillus succinogenes?

ATP synthase subunit a (atpB) is an integral membrane protein component of the F0 sector in the F1F0-ATP synthase complex in A. succinogenes. This enzyme consists of multiple subunits arranged in the structure α3:β3:γ:δ:ε:a:b2:c10, with atpB (subunit a) playing a crucial role in proton translocation across the cellular membrane. The full-length protein consists of 261 amino acids and is encoded by the atpB gene (also known as Asuc_0332) . As part of the complete ATP synthase complex, atpB contributes to the organism's energy metabolism, which is particularly important for A. succinogenes as a strictly respiratory organism that produces succinic acid as a primary metabolite .

How does recombinant atpB differ from native atpB in experimental applications?

Recombinant and native atpB exhibit several key differences that impact experimental applications:

These differences are significant for researchers designing experiments. Native atpB functions within the complete ATP synthase complex in its natural lipid environment, while recombinant atpB requires careful reconstitution approaches to study its authentic function . Researchers must consider these differences when interpreting results from in vitro studies using recombinant protein versus in vivo studies examining native protein function.

What expression systems and purification methods yield the highest purity recombinant atpB?

The expression and purification of high-quality recombinant A. succinogenes atpB requires specialized approaches:

For optimal expression in E. coli, recommended conditions include:

• Induction at lower temperature (16-20°C)

• Reduced IPTG concentration (0.1-0.5 mM)

• Extended expression time (16-24 hours)

• Addition of membrane-stabilizing compounds

A multi-step purification protocol typically yields >90% purity :

• Cell lysis in buffer containing appropriate detergents (e.g., DDM, LDAO)

• IMAC purification utilizing the His-tag

• Ion exchange chromatography as a secondary purification step

• Size exclusion chromatography for final polishing

For storage, the purified protein should be maintained in Tris/PBS-based buffer with 6% trehalose at pH 8.0 . Long-term storage requires addition of 50% glycerol and storage at -80°C, with aliquoting to avoid freeze-thaw cycles .

How does atpB contribute to energy metabolism and succinic acid production in A. succinogenes?

AtpB plays a critical role in A. succinogenes energy metabolism that indirectly impacts succinic acid production:

A. succinogenes has unique metabolic characteristics that make ATP synthase particularly important:

• It possesses an incomplete TCA cycle that natively terminates at succinic acid

• The organism is capnophilic, incorporating CO2 into succinic acid, requiring energy

• ATP generation influences the balance between biomass formation and product synthesis

Genome-scale metabolic modeling of A. succinogenes (model iBP722) has demonstrated that ATP synthase activity significantly affects calculated flux distributions under different fermentation conditions . Specifically, the model shows that carbon dioxide fixation pathways and ATP synthesis are interconnected, with the transport mechanism of carbon sources and ability to fix CO2 being crucial determinants of metabolic flux .

How stable is recombinant atpB under various storage and experimental conditions?

The stability of recombinant A. succinogenes atpB varies significantly under different conditions:

For optimal stability, commercial preparations recommend:

• Avoiding repeated freeze-thaw cycles

• Using Tris/PBS-based buffer with 6% trehalose at pH 8.0

• Adding 5-50% glycerol for long-term storage (with 50% being optimal)

• Reconstituting lyophilized protein to 0.1-1.0 mg/mL concentration

During experimental procedures, stability can be enhanced by:

• Maintaining consistent temperature (4°C during handling)

• Including appropriate detergents to maintain membrane protein solubility

• Adding reducing agents to prevent oxidation of cysteine residues

• Minimizing exposure to proteases and other degradative enzymes

These stability parameters are crucial for researchers planning long-term studies or designing experimental protocols that require consistent protein quality across multiple experimental sessions.

How can site-directed mutagenesis of atpB affect ATP synthesis/hydrolysis in experimental systems?

Site-directed mutagenesis of A. succinogenes atpB provides valuable insights into structure-function relationships of ATP synthase. Drawing from related studies on ATP synthase in A. baumannii , several key mutation targets can be identified:

Research on A. baumannii ATP synthase demonstrates that modifications to regulatory elements can dramatically impact function. For example, removal of the inhibitory ε subunit resulted in a 21.5-fold increase in ATP hydrolysis activity . Similar principles likely apply to A. succinogenes ATP synthase.

Experimental approaches should include:

• Creating mutations using overlap extension PCR or commercial site-directed mutagenesis kits

• Expressing mutant proteins in appropriate hosts

• Purifying and reconstituting mutants into liposomes or nanodiscs

• Measuring ATP synthesis/hydrolysis activities under standardized conditions

• Structural characterization using techniques like hydrogen-deuterium exchange mass spectrometry

These studies would reveal how specific residues in atpB contribute to the unique properties of A. succinogenes ATP synthase, potentially identifying targets for metabolic engineering to enhance succinic acid production.

What metabolic engineering strategies involving atpB could enhance succinic acid production?

ATP synthase engineering represents a promising but underexplored approach for enhancing succinic acid production in A. succinogenes. Several strategies can be proposed based on our understanding of ATP synthase function and A. succinogenes metabolism:

These strategies should be evaluated in the context of A. succinogenes' unique metabolism:

• The organism has an incomplete TCA cycle terminating at succinic acid

• It incorporates CO2 into succinic acid, requiring energy

• ATP availability affects the balance between growth and product formation

Implementation would utilize genetic tools developed for A. succinogenes, including:

• Homologous recombination with linear PCR fragments containing genomic homology regions

• The pLGZ920 expression vector system encoding chloramphenicol resistance

• Cre-lox systems for marker recycling in sequential genetic modifications

Genome-scale metabolic modeling (using model iBP722) would be valuable for predicting the effects of these manipulations before experimental implementation . The model contains 1072 enzymatic reactions associated with 722 metabolic genes and can simulate various growth and production conditions .

How does atpB structure in A. succinogenes compare to homologs in other bacterial species?

Comparative analysis of atpB across bacterial species reveals important evolutionary and functional insights:

Studies on A. baumannii ATP synthase provide valuable comparative insights:

• The architecture and regulatory elements visualized by cryo-EM at 3.0 Å resolution revealed the C-terminal domain of subunit ε in an extended position

• Removal of regulatory elements resulted in dramatically increased ATP hydrolysis

• Mutational studies identified critical residues for domain-domain interactions

For A. succinogenes specifically, its atpB likely contains adaptations related to:

• Its capnophilic nature and CO2 incorporation capabilities

• Role in succinic acid production as a primary fermentation product

• Ability to utilize various carbon sources including pentose and hexose sugars

Detailed structural comparison would require techniques such as:

• Homology modeling based on resolved ATP synthase structures

• Evolutionary analysis to identify conserved functional residues

• Molecular dynamics simulations to predict structure-function relationships

How can genome-scale metabolic models predict the effects of atpB modifications?

Genome-scale metabolic models (GSMMs) provide powerful platforms for predicting the effects of atpB modifications in A. succinogenes. The existing GSMM for A. succinogenes, iBP722 , offers a robust foundation for such analyses:

The iBP722 model features:

• Coverage of 1072 enzymatic reactions associated with 722 metabolic genes

• 713 metabolites involved in A. succinogenes metabolism

• Validated ability to predict growth on various carbon sources and succinic acid production

To model atpB modifications specifically:

• Identify reactions involving ATP synthase in the model

• Modify constraints to reflect expected changes in ATP synthesis efficiency

• Incorporate experimental data on ATP synthase kinetics when available

• Simulate under various media conditions and environmental parameters

• Analyze predicted flux distributions through central carbon metabolism

• Identify potential bottlenecks or unexpected consequences

The metabolic model has demonstrated that CO2 fixation pathways and ATP synthesis are interconnected, with carbon source transport mechanisms being crucial determinants of metabolic flux . This suggests that atpB modifications could have complex ripple effects throughout metabolism that can be effectively predicted using GSMM approaches.