Recombinant Kineococcus radiotolerans ATP synthase subunit b (atpF)

What is the Kineococcus radiotolerans ATP synthase subunit b (atpF) and what is its role in cellular function?

Kineococcus radiotolerans ATP synthase subunit b (atpF) is a critical component of the F-type ATP synthase complex in this extremophile organism. The protein functions as part of the peripheral stalk of ATP synthase, forming long helices that protrude from the membrane into the cellular compartment . This peripheral stalk serves as a crucial stationary component that prevents rotation of specific parts of the ATP synthase during catalysis, thereby enabling the conversion of electrochemical potential into mechanical energy for ATP production . As part of the F₀ sector, subunit b (encoded by the atpF gene, locus Krad_1266) anchors the catalytic F₁ sector to the membrane domain . In K. radiotolerans, this protein plays an essential role in energy production in a highly radiation-resistant organism that survives in radioactive environments.

What are the structural characteristics of the ATP synthase subunit b (atpF) in K. radiotolerans?

The ATP synthase subunit b in K. radiotolerans exhibits several key structural features:

• Complete amino acid sequence (188 amino acids): mLVAAFAAAGEEVEGNPTYPILPHLGELIVGIIFAIIIYAVIAKKVVPRLEAMYEERRAA IEGNVEKAEKAQAEAQVALEQYKAQLADARGEANRIREEARQQGAQILAEMREQAQAESE RITTAARATIEAERVQATAQLRAEVGRLATDLAGRIVGESLQDSARQSGVVDRFLADLER SESGASSR

• Forms a helical structure that extends from the membrane into the cellular space

• Contains a transmembrane domain (hydrophobic region evident in the N-terminal portion of the sequence)

• Features coiled-coil regions in the peripheral stalk portion that facilitate interactions with other ATP synthase subunits

The protein's UniProt accession number is A6W7G5, and it is also known by alternative names including ATP synthase F(0) sector subunit b, ATPase subunit I, and F-type ATPase subunit b .

How does the atpF gene expression correlate with K. radiotolerans' extreme radiation resistance?

While there is no direct evidence linking atpF expression specifically to radiation resistance in K. radiotolerans, several important considerations emerge from what we know about this organism:

K. radiotolerans exhibits γ-radiation resistance approaching that of Deinococcus radiodurans despite lacking many genes known to confer radiation resistance in D. radiodurans . The organism instead appears to employ unique genetic tools for radiation protection, including overrepresentation of genes involved in:

• Detoxification of reactive oxygen species

• DNA excision repair pathways

The ATP synthase complex may contribute indirectly to radiation resistance through:

• Maintaining efficient energy production under stress conditions

• Supporting metabolic processes that enable survival during radiation damage repair

• Potentially contributing to membrane integrity under radiation stress

While ATP synthase function itself may not directly confer radiation resistance, proper energy metabolism is likely crucial to power the cellular machinery that repairs radiation damage.

What experimental approaches can be used to study protein-protein interactions involving the ATP synthase subunit b in K. radiotolerans?

Several sophisticated methodologies can be employed to investigate protein-protein interactions involving the ATP synthase subunit b:

When designing these experiments, researchers should consider the unique properties of K. radiotolerans, including its high G+C content genome, thick extracellular polymer shell, and potential for unusual post-translational modifications that might influence protein interactions .

How can researchers investigate the role of post-translational modifications in K. radiotolerans ATP synthase subunit b?

Investigation of post-translational modifications (PTMs) in K. radiotolerans ATP synthase subunit b requires a multi-faceted approach:

• Mass Spectrometry (MS) Analysis:

  • Bottom-up proteomics: Enzymatic digestion followed by LC-MS/MS to identify modified peptides

  • Top-down proteomics: Analysis of intact protein to preserve modification patterns

  • Targeted MS approaches using multiple reaction monitoring (MRM) for quantification of specific PTMs

• Site-Directed Mutagenesis:

  • Systematic mutation of potential modification sites (Ser, Thr, Tyr residues for phosphorylation; Lys for acetylation)

  • Functional assays comparing wild-type and mutant proteins

• Modification-Specific Antibodies:

  • Western blotting using antibodies against common PTMs (phosphorylation, acetylation, etc.)

  • Immunoprecipitation to enrich modified forms of the protein

• ATP Synthase Activity Assays:

  • Comparison of enzyme kinetics between modified and unmodified forms

  • Investigation of how modifications affect proton translocation or ATP synthesis

• Structural Analysis:

  • X-ray crystallography or cryo-EM with and without modifications

  • Hydrogen-deuterium exchange mass spectrometry (HDX-MS) to detect conformational changes induced by PTMs

Given K. radiotolerans' extreme environment tolerance, investigating how PTMs might regulate ATP synthase activity under stress conditions (radiation, desiccation) would be particularly valuable for understanding adaptation mechanisms.

What biophysical techniques are most appropriate for studying the conformational dynamics of K. radiotolerans ATP synthase subunit b?

The helical structure and dynamic nature of ATP synthase subunit b make it an interesting target for conformational studies. Optimal techniques include:

When studying K. radiotolerans ATP synthase subunit b, researchers should consider how radiation resistance might be reflected in protein stability and dynamics. Comparative studies with homologous proteins from radiation-sensitive organisms could provide valuable insights into structural adaptations for extreme environments.

What are the optimal storage and handling conditions for recombinant K. radiotolerans ATP synthase subunit b?

Proper storage and handling are crucial for maintaining the activity and integrity of recombinant K. radiotolerans ATP synthase subunit b:

Storage Recommendations:

• Store stock solution at -20°C for routine use

• For extended storage, maintain at -80°C to prevent degradation

• Working aliquots can be stored at 4°C for up to one week

• Avoid repeated freeze-thaw cycles which can lead to protein denaturation and aggregation

Buffer Composition:

• Standard storage in Tris-based buffer with 50% glycerol, optimized for protein stability

• For functional studies, consider buffers that mimic physiological conditions (pH 7.2-7.5)

• Include protease inhibitors to prevent degradation during experimental procedures

Handling Practices:

• Maintain cold chain during all manipulations

• Centrifuge briefly after thawing to collect any precipitated material

• Consider adding reducing agents (DTT or TCEP at 0.5-1 mM) if working with the protein for extended periods

• For concentration adjustment, use gentle methods like dialysis rather than ultrafiltration which may cause aggregation

Quality Control:

• Periodically assess protein integrity by SDS-PAGE

• Verify structural integrity by circular dichroism before critical experiments

• Monitor activity through appropriate functional assays

These recommendations are based on standard practices for membrane protein components and the specific information provided for the recombinant protein product .

What expression systems have been most successful for producing functional recombinant K. radiotolerans ATP synthase subunit b?

While specific expression data for K. radiotolerans ATP synthase subunit b is limited in the provided search results, a methodological approach based on similar membrane proteins would include:

Bacterial Expression Systems:

• E. coli BL21(DE3) with specialized vectors (pET series) for membrane proteins

• E. coli C41/C43 strains (Walker strains) specifically designed for membrane protein expression

• Codon optimization is critical due to K. radiotolerans' high G+C content genome

Expression Strategies:

• Lower induction temperatures (16-25°C) to slow expression and facilitate proper folding

• Induction with lower IPTG concentrations (0.1-0.5 mM) for gentler expression

• Consider fusion tags that enhance solubility (MBP, SUMO) with cleavable linkers

Cell-Free Expression:

• PURE system supplemented with lipids or nanodiscs for transmembrane domain stabilization

• Wheat germ extract systems which may better accommodate the high G+C content of K. radiotolerans genes

Eukaryotic Systems for Complex Studies:

• Baculovirus-insect cell expression for studies requiring assembled peripheral stalk

• Yeast expression systems (P. pastoris) for higher yields of properly folded protein

For structural studies requiring the native conformation, co-expression with other ATP synthase components might be necessary to stabilize the protein in its functional form.

How can researchers verify the proper folding and activity of recombinant K. radiotolerans ATP synthase subunit b?

Verifying proper folding and activity requires a multi-faceted approach:

Structural Assessment:

• Circular Dichroism (CD) Spectroscopy: Confirm the expected high α-helical content characteristic of subunit b

• Size Exclusion Chromatography (SEC): Assess oligomeric state and aggregation profile

• Limited Proteolysis: Properly folded proteins show characteristic digestion patterns

• Thermal Shift Assays: Measure protein stability (Tm) as an indicator of proper folding

Functional Validation:

• Binding Assays with Partner Subunits: Verify interaction with other ATP synthase components

• Reconstitution Studies: Attempt incorporation into liposomes or nanodiscs

• Complementation Assays: Test ability to rescue function in ATP synthase-deficient mutants

Comparative Analysis:

• Compare structural and functional parameters with well-characterized homologs from other species

• Assess stability under radiation conditions mimicking the natural environment of K. radiotolerans

A properly folded ATP synthase subunit b should demonstrate:

• Predominantly α-helical secondary structure

• Ability to form dimers

• Specific interaction with other ATP synthase components

• Resistance to proteolytic degradation in its core helical regions

How can recombinant K. radiotolerans ATP synthase subunit b be used in studies of radiation resistance mechanisms?

Recombinant K. radiotolerans ATP synthase subunit b offers unique opportunities for radiation resistance research:

K. radiotolerans shows remarkable radiation resistance approaching that of Deinococcus radiodurans while employing different genetic strategies . Understanding how its ATP synthase components contribute to this phenotype could reveal novel mechanisms of radiation resistance.

What insights might K. radiotolerans ATP synthase subunit b provide for bioremediation applications?

K. radiotolerans has significant potential for bioremediation of nuclear waste sites, and understanding its ATP synthase function contributes to these applications:

• Energy Production in Contaminated Environments:

  • K. radiotolerans can respire on formate and oxalate found in high-level nuclear waste, which promotes survival during prolonged starvation periods

  • ATP synthase function is crucial for harvesting energy from these alternative carbon sources

• Survival Mechanisms During Bioremediation:

  • ATP synthase efficiency under radiation stress could be a determining factor in successful bioremediation applications

  • Understanding how subunit b contributes to ATP synthase stability provides insights for optimizing bioremediation strains

• Bioengineering Applications:

  • The unique properties of K. radiotolerans ATP synthase components could inspire the design of radiation-resistant biocatalysts

  • Structural features of subunit b might be transferable to other proteins to enhance their stability in extreme environments

• Metabolic Engineering for Enhanced Bioremediation:

  • Modifications to ATP synthase components, including subunit b, could potentially enhance energy efficiency in engineered bioremediation strains

  • This could lead to improved survival and contaminant processing in high-radiation environments

The remarkable ability of K. radiotolerans to withstand environmental extremes suggests that in situ bioremediation of organic complexants from high-level radioactive waste may be feasible . ATP synthase components like subunit b are integral to the energy production systems that make this possible.

How might structural studies of K. radiotolerans ATP synthase subunit b contribute to understanding ATP synthase evolution in extremophiles?

Structural analysis of K. radiotolerans ATP synthase subunit b offers valuable evolutionary insights:

• Comparative Genomics and Proteomics:

  • Alignment with homologs from other extremophiles and mesophiles to identify conserved vs. adaptive features

  • Identification of residues under positive selection that might contribute to extremophile adaptation

• Structure-Function Relationships:

  • Determination of how structural adaptations in K. radiotolerans subunit b might contribute to ATP synthase stability under extreme conditions

  • Analysis of coevolution between subunit b and other ATP synthase components

• Evolutionary Trajectories in Extreme Environments:

  • Reconstruction of the evolutionary history of ATP synthase components in radiation-resistant organisms

  • Identification of convergent evolution patterns in unrelated extremophiles

• Ancestral Sequence Reconstruction:

  • Computational reconstruction of ancestral sequences to trace the emergence of radiation-resistant features

  • Experimental characterization of resurrected ancestral proteins to test evolutionary hypotheses

These studies could reveal whether adaptations in ATP synthase components represent general strategies for surviving extreme conditions or lineage-specific innovations. K. radiotolerans presents a particularly interesting case as it evolved radiation resistance independently from the well-studied Deinococcus lineage .