Recombinant Shewanella baltica ATP synthase subunit b (atpF)

What is Shewanella baltica ATP synthase subunit b and what are its key characteristics?

Shewanella baltica ATP synthase subunit b (atpF) is a critical component of the F-type ATP synthase complex, specifically part of the F₀ sector that spans the bacterial membrane. This protein is also known as ATP synthase F₀ sector subunit b, ATPase subunit I, or F-ATPase subunit b . The full-length protein consists of 156 amino acids with a molecular weight of approximately 17-18 kDa.

The amino acid sequence of Shewanella baltica atpF (strain OS155) is MNFNATLIGQTVAFIIFVWFCMKFVWPPLMNAIEERQKRIADGLADADRAVKDLELAQAKATDQLKEAKVTANEIIEQANKRKAQIVEEAKTEANAERAKIIAQGKAEIEAERNRVKEDLRKQVATLAIMGAEKILERSIDPAAHSDIVNKLVAEI . The protein features a hydrophobic N-terminal region that anchors it in the membrane and a more hydrophilic C-terminal domain that extends into the cytoplasm and interacts with other components of the ATP synthase complex.

Functionally, subunit b serves as a critical part of the peripheral stalk (or stator) of ATP synthase, connecting the membrane-embedded F₀ sector to the catalytic F₁ sector. This structural role is essential for maintaining the relative positions of the rotating and stationary parts of the enzyme during the catalytic cycle.

How should recombinant Shewanella baltica ATP synthase subunit b be stored and handled for optimal stability?

Proper storage and handling of recombinant Shewanella baltica ATP synthase subunit b is crucial for maintaining its structural integrity and biological activity. The recommended storage conditions include keeping the protein at -20°C for regular use, or at -80°C for extended storage periods . The protein is typically supplied in a Tris-based buffer containing 50% glycerol, which has been optimized for protein stability .

To minimize protein degradation during experimental procedures, it is advisable to avoid repeated freeze-thaw cycles, as these can lead to protein denaturation and loss of activity . Instead, researchers should prepare working aliquots that can be stored at 4°C for up to one week . This approach balances convenience with the need to preserve protein integrity.

The shelf life of the recombinant protein varies depending on storage conditions. Generally, liquid formulations have a shelf life of approximately 6 months when stored at -20°C or -80°C, while lyophilized forms can remain stable for up to 12 months under the same conditions . Factors affecting shelf life include buffer composition, storage temperature, and the intrinsic stability of the protein itself.

What expression systems are suitable for producing recombinant Shewanella baltica ATP synthase subunit b?

Recombinant Shewanella baltica ATP synthase subunit b is typically produced using in vitro E. coli expression systems . This approach is preferred due to the relative simplicity of bacterial expression systems and their ability to produce sufficient quantities of properly folded membrane proteins. The protein is commonly expressed with an N-terminal 10xHis-tag to facilitate purification through affinity chromatography .

When designing expression strategies for this transmembrane protein, researchers should consider:

• Selection of appropriate E. coli strains optimized for membrane protein expression

• Induction conditions that balance protein yield with proper folding

• Solubilization methods that effectively extract the protein from bacterial membranes while preserving its native structure

• Purification protocols that minimize aggregation while maximizing purity

The expression region typically encompasses the full-length protein (residues 1-156) , ensuring that all functional domains are present in the recombinant product. This is particularly important for structural and functional studies where complete protein architecture is essential.

How does the structure of bacterial ATP synthase subunit b contribute to the rotational mechanics of the enzyme?

The structure of bacterial ATP synthase subunit b plays a crucial role in the rotational mechanics of the enzyme complex. Based on cryo-EM studies of bacterial ATP synthases, subunit b forms part of the peripheral stalk (stator) that prevents the catalytic F₁ head from rotating with the central rotor during ATP synthesis or hydrolysis .

Structural analyses reveal that the C-terminal water-soluble portion of subunit b displays significant conformational variability between different rotational states of the enzyme . This flexibility appears to be a key feature, as subunit b must accommodate the rotational movements of the c-ring and central stalk while maintaining structural integrity of the complex. In Bacillus PS3 ATP synthase, the peripheral stalk (which includes subunit b) is structurally simpler and more flexible than its counterparts in more complex organisms like yeast mitochondria .

The peripheral stalk serves as a critical connection between the F₁ and F₀ regions of the complex. During rotation, the c-ring and subunit a are primarily held together by hydrophobic interactions rather than by the peripheral stalk itself . This arrangement allows for the efficient transmission of energy between the proton-translocating F₀ sector and the ATP-synthesizing F₁ sector while preventing futile rotation of the entire complex.

Comparisons between bacterial ATP synthases from different species (such as Bacillus PS3 and E. coli) have revealed significant structural differences in the transmembrane α-helices of subunit b relative to subunit a . These differences may reflect species-specific adaptations in the rotational mechanics of the enzyme.

What structural differences exist between Shewanella baltica ATP synthase subunit b variants across different strains?

The sequence comparison is presented in the table below:

• The strength or specificity of protein-protein interactions

• The flexibility of the peripheral stalk

• The response to changes in pH or ionic strength

Further structural and functional studies would be needed to determine whether this single amino acid difference has any significant impact on the function of ATP synthase in these two Shewanella baltica strains.

How does bacterial ATP synthase subunit b structure compare with equivalent components in other organisms?

Bacterial ATP synthase subunit b shows significant structural and functional differences compared to its counterparts in mitochondrial and chloroplast ATP synthases . These differences reflect the evolutionary adaptations of the ATP synthase complex to different cellular environments.

A notable structural feature in bacterial ATP synthases is that loops in subunit a fill roles that are performed by additional subunits in the F₀ region of mitochondrial enzymes . This evolutionary difference highlights how the bacterial ATP synthase achieves the same functional outcomes with a more streamlined structure.

The conformational states of the catalytic subunits also differ between bacterial and mitochondrial/chloroplast ATP synthases. In Bacillus PS3, the three catalytic β subunits adopt 'open', 'closed', and 'open' conformations, which differs from the 'half-closed', 'closed', and 'open' conformations seen in E. coli F₁-ATPase, and the 'closed', 'closed', and 'open' conformations observed in chloroplast and most mitochondrial ATP synthases . These differences in conformational states suggest species-specific mechanisms of catalysis and regulation.

What analytical techniques are most effective for studying the structure-function relationship of Shewanella baltica ATP synthase subunit b?

To effectively study the structure-function relationship of Shewanella baltica ATP synthase subunit b, researchers should employ a combination of complementary analytical techniques:

• Cryo-Electron Microscopy (Cryo-EM): This technique has proven highly effective for resolving the structure of intact ATP synthase complexes at near-atomic resolution, as demonstrated by studies on Bacillus PS3 ATP synthase which achieved resolutions of 3.0-3.2 Å . Cryo-EM can capture different rotational states of the enzyme and reveal the conformational flexibility of subunit b during the catalytic cycle.

• X-ray Crystallography: While challenging for membrane proteins, crystallography can provide high-resolution structural information for isolated domains of subunit b or for the protein in complex with stabilizing partners.

• Site-Directed Mutagenesis: Systematic mutation of specific residues in subunit b, particularly at the interfaces with other subunits, can provide valuable insights into structure-function relationships. The mutations should target:

  • The membrane-spanning region

  • The interface with subunit a

  • The connection to the F₁ sector

  • Regions showing conformational flexibility between rotational states

• Crosslinking Studies: Chemical crosslinking combined with mass spectrometry can identify interaction partners and contact points between subunit b and other components of the ATP synthase complex.

• Molecular Dynamics Simulations: Computational approaches can model the dynamic behavior of subunit b within the lipid bilayer and predict conformational changes during the catalytic cycle.

What are the key considerations when designing experiments to investigate the role of subunit b in bacterial ATP synthase function?

When designing experiments to investigate the role of Shewanella baltica ATP synthase subunit b, researchers should consider several critical factors:

How can researchers effectively compare ATP synthase subunit b from Shewanella baltica with homologs from other bacterial species?

Effective comparison of ATP synthase subunit b across bacterial species requires a multifaceted approach combining sequence analysis, structural studies, and functional characterization:

• Sequence Analysis Methodology:

  • Perform multiple sequence alignments using tools like Clustal Omega or MUSCLE

  • Identify conserved domains, motifs, and residues across species

  • Calculate evolutionary conservation scores for each position

  • Generate phylogenetic trees to visualize evolutionary relationships

  • Map sequence conservation onto available structural models

• Structural Comparison Approach:

  • Align available structures using tools like PyMOL or UCSF Chimera

  • Quantify root-mean-square deviation (RMSD) between aligned structures

  • Compare secondary structure elements and domain organization

  • Analyze differences in transmembrane topology

  • Examine interfaces with other ATP synthase subunits

• Functional Comparison Strategies:

  • Design chimeric proteins swapping domains between species

  • Perform complementation studies in knockout strains

  • Measure ATP synthesis/hydrolysis rates under standardized conditions

  • Assess proton translocation efficiency

  • Compare stability and assembly of the ATP synthase complex

• Environmental Adaptation Analysis:

  • Correlate structural and functional differences with the native environment of each species

  • Examine temperature, pH, and salt tolerance of ATP synthases from different species

  • Investigate adaptations to specific ecological niches

Recent comparative studies between Bacillus PS3 and E. coli ATP synthases have revealed significant structural differences in transmembrane α-helices of subunit b relative to subunit a . Such comparisons provide valuable insights into both conserved features essential for ATP synthase function and species-specific adaptations that may reflect environmental specialization.

How should researchers interpret differences in ATP synthase subunit b conformations observed across different rotational states?

The interpretation of conformational differences in ATP synthase subunit b across rotational states requires careful consideration of several factors:

By integrating structural information across multiple rotational states with functional data, researchers can develop a comprehensive understanding of how the dynamic properties of subunit b contribute to the mechanical coupling between proton translocation and ATP synthesis in bacterial ATP synthases.

What are common challenges in purifying and working with recombinant Shewanella baltica ATP synthase subunit b, and how can they be addressed?

Working with recombinant Shewanella baltica ATP synthase subunit b presents several challenges due to its nature as a transmembrane protein. Here are common issues and methodological solutions:

• Expression Challenges:

  • Issue: Low expression levels in heterologous systems

  • Solution: Optimize codon usage for E. coli, use specialized expression strains (C41/C43), and test different induction conditions (temperature, IPTG concentration, induction time)

• Protein Solubilization:

  • Issue: Incomplete extraction from membranes or protein aggregation

  • Solution: Screen multiple detergents (DDM, LMNG, CHAPS) at various concentrations; consider using newer amphipathic polymers like SMALPs (styrene-maleic acid lipid particles) for extraction with native lipid environment

• Purification Challenges:

  • Issue: Co-purification of contaminants despite His-tag purification

  • Solution: Implement multi-step purification strategies combining affinity chromatography with size exclusion and/or ion exchange chromatography; optimize wash buffers to reduce non-specific binding

• Protein Stability:

  • Issue: Protein degradation during storage and handling

  • Solution: Store in optimized buffer with 50% glycerol at -20°C or -80°C ; avoid repeated freeze-thaw cycles; prepare working aliquots for short-term use at 4°C

• Structural Characterization:

  • Issue: Difficulty obtaining structural information in isolation

  • Solution: Consider studying subunit b within the context of larger subcomplexes or the intact ATP synthase; use stabilizing nanobodies or fusion partners to improve structural stability

• Functional Reconstitution:

  • Issue: Loss of functionality after purification

  • Solution: Reconstitute into liposomes with native-like lipid composition; verify proper orientation in the membrane; co-reconstitute with interaction partners

• Aggregation During Concentration:

  • Issue: Protein aggregation at higher concentrations needed for structural studies

  • Solution: Use spin concentrators with appropriate molecular weight cutoffs; add stabilizing agents like glycerol or specific lipids; concentrate at lower temperatures

By addressing these challenges with appropriate methodological adaptations, researchers can successfully work with recombinant Shewanella baltica ATP synthase subunit b for structural and functional studies.

What are promising research directions for understanding the role of ATP synthase subunit b in bacterial energy metabolism?

Several promising research directions could significantly advance our understanding of ATP synthase subunit b in bacterial energy metabolism:

These research directions could not only enhance our fundamental understanding of bacterial ATP synthases but also potentially lead to applications in biotechnology, synthetic biology, and drug development.

How might single amino acid differences between Shewanella baltica strains impact ATP synthase function and bacterial physiology?

The single amino acid difference identified between ATP synthase subunit b from Shewanella baltica strains OS155 (Glu102) and OS185 (Asp102) presents an intriguing opportunity to investigate the functional significance of seemingly minor sequence variations. Several methodological approaches could elucidate the potential impacts:

• Structural Impact Analysis:

  • Molecular dynamics simulations to compare local structural dynamics

  • Hydrogen bonding network analysis to identify altered interaction patterns

  • Electrostatic surface mapping to detect changes in charge distribution

• Functional Comparison Studies:

  • ATP synthesis/hydrolysis rate measurements under various conditions

  • Proton pumping efficiency comparisons

  • Thermal stability assessments of the peripheral stalk

• Ecological Correlation:

  • Analysis of the native environments of each strain (temperature, pH, salt concentration)

  • Investigation of whether the amino acid difference correlates with specific adaptations

  • Comparative growth studies under various environmental stresses

• Site-Directed Mutagenesis Approach:

  • Creation of reciprocal mutations (E102D in OS155 and D102E in OS185)

  • Functional characterization of the mutants compared to wild-type proteins

  • Construction of chimeric proteins to identify potential epistatic interactions

• Evolutionary Context Examination:

  • Phylogenetic analysis of position 102 across Shewanella species

  • Assessment of whether this position is under selective pressure

  • Investigation of the prevalence of Glu vs. Asp at this position in related species

This research direction exemplifies how detailed investigation of subtle sequence variations can provide insights into the fine-tuning of essential cellular machinery like ATP synthase, potentially revealing mechanisms of bacterial adaptation to specific ecological niches.