Recombinant Shewanella halifaxensis ATP synthase subunit a (atpB)

What is the structure and function of ATP synthase in Shewanella halifaxensis?

ATP synthase in Shewanella halifaxensis, like in other organisms, is a multimeric protein complex that catalyzes ATP synthesis. The enzyme consists of two major domains: the F₁ domain with catalytic activity located in the cytoplasm, and the F₀ domain embedded in the membrane forming a proton channel. The complete structure includes multiple subunits (α₃β₃γδεab₂c₁₀₋₁₄) that work together in the rotational catalysis mechanism .

In Shewanella species, ATP synthase exhibits some unique characteristics compared to other bacteria. Notably, while ATP synthase typically functions in ATP synthesis coupled to a proton gradient, research has shown that in Shewanella oneidensis (a related species), substrate-level phosphorylation is actually the primary source of ATP under anaerobic conditions, with ATP synthase playing a secondary role .

How does the sequence of ATP synthase subunit b (atpF) from Shewanella halifaxensis compare to other bacterial species?

The ATP synthase subunit b (atpF) in Shewanella halifaxensis (strain HAW-EB4) consists of 156 amino acids with the sequence: MSINATLLGQAISFLLFVWFCMKFVWPPLMNAIEERQKKIADGLADAGRAAKDLELAQVKATEQLKDAKATANEIIEQANKRKAQIVDEAKVEADTERAKIIAQGHAEIENERNRVKEDLRKQVAALAIAGAEKILERSIDEAAHSDIVNKLVAEL .

This sequence contains regions that facilitate its membrane anchoring and participation in the stator structure of ATP synthase. While detailed comparative analyses aren't provided in the search results, the general structure maintains the functional domains necessary for ATP synthase operation, including regions that interact with other subunits to form the mechanical units involved in rotational catalysis .

What are the optimal conditions for expressing recombinant Shewanella halifaxensis ATP synthase subunits in E. coli?

While the search results don't provide specific expression protocols for S. halifaxensis ATP synthase subunits, researchers typically optimize several parameters:

Expression System Selection:

• BL21(DE3) or similar E. coli strains designed for high-level protein expression

• Temperature: Often lowered to 18-25°C during induction to enhance protein folding

• Induction: IPTG concentration typically between 0.1-1.0 mM depending on construct

Buffer Optimization:
Based on available recombinant protein information, storage conditions for the purified protein include:

• Tris-based buffer with 50% glycerol

• Storage at -20°C for short-term or -80°C for extended storage

• Avoiding repeated freeze-thaw cycles

Researchers should perform small-scale expression trials varying induction time, temperature, and IPTG concentration to determine optimal conditions for their specific construct.

What purification methods are most effective for isolating recombinant ATP synthase subunits?

Effective purification of ATP synthase subunits typically involves a multi-step approach:

1. Affinity Chromatography:

• His-tag purification for subunits engineered with histidine tags

• Biotin-tag systems for specific experimental setups requiring immobilization

2. Additional Purification Steps:

• Ion exchange chromatography to separate based on charge properties

• Size exclusion chromatography for final polishing and buffer exchange

Purification Buffer Considerations:

• Inclusion of protease inhibitors

• Optimized pH (typically 7.0-8.0)

• Appropriate salt concentration (typically 100-300 mM NaCl)

• Addition of glycerol (10-20%) to enhance stability

For functional studies, membrane protein extraction requires careful detergent selection, with commonly used detergents including n-dodecyl-β-D-maltoside (DDM) or digitonin at concentrations above their critical micelle concentration .

How can researchers study the rotational dynamics of ATP synthase using recombinant subunits?

Studying rotational dynamics of ATP synthase requires sophisticated experimental setups:

Engineering Approach:
Researchers can follow strategies similar to those described by Noji and colleagues:

• Introduce biotin-tags onto specific subunits (β or a)

• Add His-tags to the c subunit ring

• Immobilize membrane fragments containing the engineered ATP synthase on glass surfaces

• Attach fluorescent markers (like actin filaments) to the biotinylated subunits

• Observe rotation using fluorescence microscopy upon ATP addition

Expected Results:

• Counterclockwise rotation can be observed upon ATP addition

• Rotational torque measurements provide insights into the mechanical force generated

• Comparing rotation patterns between different constructs helps elucidate the mechanical coupling between subunits

This approach allows direct visualization of conformational changes during the catalytic cycle and can reveal the mechanical basis of energy conversion.

How does pH affect the conformation and function of ATP synthase, and what methods can detect these changes?

Recent research has revealed that pH significantly impacts ATP synthase conformation and function:

pH Effects on ATP Synthase:

• At acidic pH, ATP synthase adopts four distinct conformations

• Three conformations represent different stages in the reaction cycle

• Two unique states exist under acidic conditions that aren't observed at neutral pH

Methodological Approaches:

• Cryo-electron Microscopy (Cryo-EM):

  • Allows visualization of ATP synthase conformations at different pH values

  • Can detect subtle conformational changes in the F₁-F₀ coupling region

• Multi-omics Approach:

  • Spatial proteomics: Identifies location and distribution of ATP synthase components

  • Interaction proteomics: Maps protein-protein interactions under different pH conditions

  • Transcriptomics: Reveals changes in gene expression related to ATP synthase

• pH-dependent Activity Assays:

  • ATP synthesis/hydrolysis rates measured across pH range

  • Conformational probes to detect structural changes

Understanding these pH-dependent conformational changes is particularly relevant for conditions like hypoxia, where tissues become acidic, affecting ATP synthase function in diseases like cancer and cardiac ischemia .

What role does ATP synthase play in Shewanella species under anaerobic conditions?

In Shewanella species, ATP synthase plays a surprisingly secondary role in energy production under anaerobic conditions:

Primary ATP Production Mechanism:

• Substrate-level phosphorylation is the primary source of ATP in anaerobic conditions

• Genes ackA (SO2915) and pta (SO2916) are crucial for acetate production and substrate-level ATP generation

• Mutants lacking these genes cannot grow anaerobically with lactate and fumarate

ATP Synthase Function:

• Deletion of F-type ATP synthase (SO4746 to SO4754) shows only minor growth defects with lactate under anaerobic conditions

• ATP synthase mutants expressing proteorhodopsin (a light-dependent proton pump) show restored growth when exposed to light

• This suggests ATP synthase functions primarily in proton pumping rather than ATP synthesis under these conditions

Research Implications:
This unusual energy conservation strategy appears to be common across Shewanella species based on genomic analysis and phenotypic characterization of multiple strains. Understanding this mechanism is crucial for researchers studying Shewanella's unique respiratory capabilities, including its ability to reduce extracellular electron acceptors like metals and electrodes .

What antibodies and detection methods are most reliable for studying ATP synthase subunits in Shewanella?

While specific antibodies for Shewanella halifaxensis ATP synthase aren't detailed in the search results, researchers can consider:

Antibody Options:

• Commercial Antibodies:

  • Polyclonal antibodies against conserved regions of ATP synthase β subunit, such as those available from Agrisera (AS16 3976)

  • These antibodies are raised against synthetic peptides derived from conserved sequences

• Custom Antibody Development:

  • Using synthetic peptides derived from Shewanella-specific sequences

  • KLH-conjugated peptides are effective immunogens for raising polyclonal antibodies

Detection Methods:

• Western Blot Analysis:

  • Recommended dilutions: 1:1000-1:5000 for most anti-ATP synthase antibodies

  • Expected molecular weight: ~55-60 kDa for the β subunit

• Sample Preparation:

  • Mitochondrial or bacterial membrane proteins should be carefully isolated

  • Denaturation typically at 80°C for 10 minutes in standard sample buffer containing SDS and β-mercaptoethanol

Researchers working with Shewanella should validate antibody cross-reactivity, as some antibodies developed against model organisms may have variable reactivity with Shewanella proteins.

How can researchers effectively compare ATP synthase function between different Shewanella species?

Comparing ATP synthase function between Shewanella species requires a multi-faceted approach:

Comparative Genomic Analysis:

• Sequence alignment of ATP synthase subunit genes (atpA-H) across Shewanella species

• Identification of conserved domains and species-specific variations

Functional Assays:

• Growth Phenotyping:

  • Compare growth of wild-type and ATP synthase mutants under various conditions:

    • Aerobic vs. anaerobic environments

    • Different carbon sources (lactate, N-acetylglucosamine, etc.)

    • Various electron acceptors (oxygen, fumarate, metal oxides)

• ATP Synthesis Measurement:

  • Luciferase-based ATP quantification assays

  • Comparison of ATP production rates under standardized conditions

• Proton Pumping Assays:

  • pH-sensitive fluorescent dyes to monitor proton translocation

  • Light-dependent growth recovery using heterologous proton pumps like proteorhodopsin

This comparative approach can reveal functional differences in ATP synthase across Shewanella species and provide insights into their diverse energy conservation strategies.

What is known about the trafficking and surface localization of ATP synthase in bacterial systems?

Recent research on eukaryotic systems has revealed surprising aspects of ATP synthase trafficking that may inform bacterial studies:

Ectopic ATP Synthase:

• ATP synthase complexes can be found on cancer cell surfaces (eATP synthase)

• These surface-localized complexes generate ATP in the extracellular environment

Trafficking Mechanism (in eukaryotes):

• Initial assembly in mitochondria

• Delivery to cell surface along microtubules via:

  • Dynamin-related protein 1 (DRP1)

  • Kinesin family member 5B (KIF5B)

• Mitochondrial membrane fusion with plasma membrane to anchor ATP synthase

While this specific mechanism is described for eukaryotic cells, it raises interesting questions about potential surface localization of ATP synthase in bacterial systems like Shewanella. Researchers could investigate whether similar trafficking or surface expression occurs in bacterial cells using techniques such as:

• Surface protein biotinylation

• Fluorescence microscopy with non-permeabilized cells

• Activity assays on intact cells vs. membrane fractions