Recombinant Psychromonas ingrahamii ATP synthase subunit b (atpF)

What is the basic structure of Psychromonas ingrahamii ATP synthase subunit b (atpF)?

Psychromonas ingrahamii ATP synthase subunit b (atpF) is a 156-amino acid protein with the sequence: "MNINATLLGQAIAFAVFVWFCMKYVWPPLLAAIEDRQKKISDGLTQAERAGKDLELAQAKASEKLKEAKVQAAEIIEQANKRRNQIVEAAKTEAETERQKIIAQGEAEVEVDRNRVREELRLKVSALAIAGAEKIIKRSIDKEANSDIIDKLVAEL" . The protein is part of the F₀ sector of the ATP synthase complex in P. ingrahamii (strain 37). The gene is identified by the locus name Ping_3734 in the genome and has the UniProt accession number A1T0Z3 .

The protein contains several key structural features typical of ATP synthase b subunits, including:

• N-terminal membrane-spanning regions

• Helical domains involved in dimerization

• C-terminal regions that interact with the F₁ sector

What are the critical differences between Psychromonas ingrahamii atpF and homologous proteins from mesophilic bacteria?

Based on comparative analyses of extremophilic proteins, P. ingrahamii atpF likely exhibits several key differences from mesophilic counterparts:

These adaptations allow the protein to maintain sufficient flexibility for function at very low temperatures . Comparative modeling studies of proteins from psychrophilic, mesophilic, and thermophilic bacteria show that psychrophilic proteins generally have adaptations that reduce structural rigidity .

What are the optimal conditions for expressing recombinant P. ingrahamii atpF in heterologous systems?

For optimal expression of recombinant P. ingrahamii atpF:

• Expression System Selection:

  • E. coli BL21(DE3) is recommended for initial expression trials

  • Cold-adapted expression hosts like ArcticExpress™ may improve protein folding

• Temperature Optimization:

  • Induction at 15-18°C for 16-24 hours typically yields better results than standard 37°C protocols

  • This mimics the native low-temperature environment of P. ingrahamii

• Buffer Composition:

  • Include 10-15% glycerol in buffers to maintain protein stability

  • Use Tris-based buffers (pH 7.2-8.0) supplemented with 100-150 mM NaCl

  • Addition of reducing agents like 1-5 mM β-mercaptoethanol may improve stability

• Induction Parameters:

  • Lower IPTG concentrations (0.1-0.3 mM) often yield better results than standard 1 mM

  • Consider auto-induction media for cold-temperature expression

Researchers should monitor expression with SDS-PAGE and Western blotting using antibodies against the added tag or against conserved regions of ATP synthase b subunits.

What are the recommended approaches for structural studies of Psychromonas ingrahamii atpF?

Several approaches have proven effective for structural characterization of ATP synthase components from extremophiles:

• Comparative Modeling:

  • iTasser has been successfully used for initial structure prediction of extremophilic proteins, with better results than AlphaFold for certain extremophilic proteins

  • Models should undergo in silico maturation including signal sequence removal and protonation state adjustment using PROPKA3

• Molecular Dynamics (MD) Simulations:

  • Equilibration in explicit solvent using atomistic molecular dynamics

  • Analysis of protein structure networks (PSNs) to examine cohesion patterns

  • Comparison with homologous proteins using arc-cosine kernel models and PCA for dimensional reduction

• Experimental Structure Determination:

  • X-ray crystallography after co-crystallization with other F₀ components

  • Cryo-EM of the intact ATP synthase complex

  • Solution NMR of isolated domains

• Functional Validation:

  • Site-directed mutagenesis to test key residues identified in structural studies

  • ATP synthesis/hydrolysis assays in reconstituted systems

How can researchers effectively analyze the thermal adaptation mechanisms of P. ingrahamii atpF?

To analyze thermal adaptation mechanisms:

• Comparative Sequence Analysis:

  • Align sequences from psychrophilic, mesophilic, and thermophilic species

  • Use Ward's algorithm and multidimensional scaling to cluster sequences by similarity

  • Identify conserved motifs across thermal groups

• Network Analysis:

  • Convert protein structures to protein structure networks (PSNs)

  • Analyze degree and k-core statistics as measures of structural cohesion

  • Compare network properties across thermal groups

• Hydrogen Bond and Salt Bridge Quantification:

  • Calculate total H-bonds and salt bridges across simulations at different temperatures

  • Compare occupancy patterns between thermal groups

  • Analyze distribution patterns spatially within the protein structure

• Active Site Dynamics Analysis:

  • Use random feature projections of interatomic distance matrices

  • Apply dimensional reduction techniques (PCA) to identify major conformational states

  • Compare conformational ensembles across thermal groups

• Experimental Validation:

  • Circular dichroism at varying temperatures to assess secondary structure stability

  • Differential scanning calorimetry to determine melting temperatures

  • Activity assays across temperature ranges

How does P. ingrahamii atpF contribute to cold adaptation of the ATP synthase complex?

P. ingrahamii atpF likely contributes to cold adaptation through several mechanisms:

• Structural Flexibility:

  • Decreased number of proline residues reduces rigidity in key regions

  • Increased glycine content allows greater conformational freedom

  • Modified loop regions maintain function at low temperatures

• Interaction Modification:

  • Reduced number of salt bridges compared to mesophilic homologs

  • Altered hydrogen bonding patterns to maintain necessary interactions at low temperatures

  • Optimized hydrophobic interactions that function at cold temperatures

• Energy Coupling Efficiency:

  • Specialized coupling between proton translocation and ATP synthesis at low temperatures

  • Modified interactions with other ATP synthase subunits to maintain efficient energy transfer

• Membrane Interaction:

  • Adaptations in the transmembrane region to function within cold-adapted membranes

  • Specialized lipid interactions that maintain function in the psychrophilic membrane environment

Studies of other psychrophilic proteins suggest these adaptations allow maintaining sufficient catalytic activity and necessary flexibility at extremely low temperatures .

What experimental evidence supports the role of atpF in P. ingrahamii's ability to grow at subzero temperatures?

• Comparative Studies:

  • Analyses of extremophilic proteins show clear patterns of adaptation in ATP synthase components

  • Psychrophilic proteins typically exhibit reduced structural rigidity compared to mesophilic counterparts

• Membrane Energetics:

  • P. ingrahamii depends on proton gradients for energy production at subzero temperatures

  • Experiments with protonophores like TCS show complete inhibition of growth in related organisms, demonstrating the essential nature of proton gradient maintenance

• Molecular Dynamics Studies:

  • Simulations of psychrophilic proteins reveal distinctive patterns of flexibility and interaction strength

  • Greater conformational space exploration at low temperatures compared to mesophilic homologs

• Structure-Function Relationships:

  • The stator function of the b subunit requires appropriate flexibility-stability balance

  • Psychrophilic adaptations in atpF would maintain this balance at extremely low temperatures

Researchers investigating this area should consider targeted mutagenesis experiments to replace psychrophilic-specific residues with mesophilic equivalents to directly test their contribution to cold adaptation.

How does P. ingrahamii atpF compare to related subunits in the ATP synthase complex?

The relationship between atpF and other ATP synthase components in P. ingrahamii reveals important structural and functional insights:

The most significant interaction is with the a subunit (atpB), as together they form crucial parts of the proton translocation machinery . The entire complex functions as a molecular motor where the proton gradient drives rotation of the c-ring (atpE oligomer), which in turn drives conformational changes in the F₁ sector to synthesize ATP .

What insights can be gained from comparing P. ingrahamii atpF with homologs from other extremophiles?

Comparative analysis of atpF across extremophiles reveals adaptive patterns:

• Psychrophiles vs. Thermophiles:

  • Thermophilic ATP synthase b subunits contain more charged residues and form more salt bridges

  • Psychrophilic variants like P. ingrahamii atpF show fewer ionic interactions but maintain functional capacity

  • Thermophiles compensate for thermal instability by increasing the number of potential bonds

• Halophiles vs. Non-halophiles:

  • Halophilic variants typically contain more acidic residues on the surface

  • P. ingrahamii, while psychrophilic, also inhabits marine environments and may show intermediate adaptations

• Evolutionary Conservation:

  • Certain regions, particularly those involved in F₁ interaction, show high conservation across extremophiles

  • Membrane-spanning regions show greater divergence, likely reflecting adaptation to different membrane compositions

• Domain Architecture:

  • Comparative models show that the basic architecture of ATP synthase is preserved across extremophiles

  • Adaptations primarily involve substitutions that modify flexibility and interaction strength rather than major structural rearrangements

These comparisons suggest that evolutionary adaptations to extreme environments follow predictable patterns that maintain functionality while adjusting stability parameters appropriate to the environmental conditions.

How can recombinant P. ingrahamii atpF be utilized in bioenergetic research?

Recombinant P. ingrahamii atpF offers several valuable applications in bioenergetic research:

• Cold-Active ATP Synthase Studies:

  • Investigation of energy conversion efficiency at low temperatures

  • Comparison with mesophilic systems to understand temperature-dependent energetic constraints

  • Analysis of proton translocation mechanics under cold conditions

• Chimeric ATP Synthase Construction:

  • Creation of hybrid ATP synthases containing psychrophilic components in mesophilic backgrounds

  • Identification of minimal modifications needed for cold adaptation

  • Development of ATP synthases with novel temperature responses

• Biophysical Model Systems:

  • Reconstitution studies in liposomes to measure proton pumping efficiency

  • Single-molecule studies of stator function under varying temperature conditions

  • Investigation of protein-lipid interactions in cold-adapted membranes

• Structure-Based Drug Design:

  • Utilizing structural insights from P. ingrahamii atpF to develop targeted antibiotics

  • Identification of psychrophile-specific features that could be exploited for selective inhibition

• Biomimetic Energy Systems:

  • Development of cold-active bioenergetic devices

  • Inspiration for synthetic biology approaches to low-temperature energy conversion

What methodological approaches should be used when studying interactions between P. ingrahamii atpF and other ATP synthase components?

To effectively study interactions between atpF and other ATP synthase components:

• Co-Immunoprecipitation Studies:

  • Generate antibodies against P. ingrahamii atpF or use tagged recombinant versions

  • Perform pull-down assays under native conditions

  • Analyze interacting partners using mass spectrometry

• Crosslinking Mass Spectrometry:

  • Apply chemical crosslinkers to stabilize transient interactions

  • Digest crosslinked complexes and analyze by mass spectrometry

  • Map interaction surfaces between atpF and partner proteins

• FRET-Based Approaches:

  • Generate fluorescently labeled atpF and potential interaction partners

  • Measure FRET efficiency to determine proximity and orientation

  • Perform temperature-dependent FRET to assess interaction dynamics

• Surface Plasmon Resonance:

  • Immobilize atpF on sensor chips

  • Measure binding kinetics with other ATP synthase components

  • Determine temperature effects on association/dissociation rates

• Cryo-EM of Reconstituted Complexes:

  • Reconstitute ATP synthase complexes with recombinant components

  • Analyze structures at different temperatures

  • Generate 3D models of the intact complex

• Molecular Dynamics Simulations:

  • Model interfaces between atpF and other components

  • Simulate dynamics at different temperatures

  • Calculate interaction energies and identify key residues

What are the major challenges in purifying functional recombinant P. ingrahamii atpF?

Researchers face several challenges when purifying functional recombinant P. ingrahamii atpF:

• Membrane Association:

  • The N-terminal region of atpF includes a membrane-spanning domain

  • Solution: Use mild detergents (0.5-1% DDM or 1-2% CHAPS) during extraction; consider expressing truncated constructs lacking the transmembrane region for certain applications

• Protein Solubility:

  • Hydrophobic regions can cause aggregation during expression

  • Solution: Optimize buffer conditions with 10-15% glycerol; consider fusion tags like MBP that enhance solubility; use low-temperature expression protocols

• Native Conformation Maintenance:

  • Ensuring proper folding is challenging for proteins adapted to extreme conditions

  • Solution: Use cold-adapted expression systems; include molecular chaperones during expression; perform refolding if necessary in cold-adapted buffer systems

• Oligomeric State:

  • Native atpF functions as a dimer in the ATP synthase complex

  • Solution: Include crosslinking studies to verify oligomeric state; use size exclusion chromatography to isolate properly formed complexes

• Storage Stability:

  • Psychrophilic proteins often show decreased stability during storage

  • Solution: Store at -80°C in buffer containing 50% glycerol; avoid repeated freeze-thaw cycles; store working aliquots at 4°C for up to one week

How can researchers validate the functionality of purified recombinant P. ingrahamii atpF?

To validate functionality of purified recombinant atpF:

• Structural Integrity Assessment:

  • Circular dichroism (CD) spectroscopy to confirm secondary structure

  • Size exclusion chromatography to verify proper oligomeric state

  • Limited proteolysis to assess proper folding

• Binding Assays:

  • Interaction studies with other ATP synthase components (particularly the F₁ sector)

  • Surface plasmon resonance with natural binding partners

  • Pull-down assays with other subunits of the ATP synthase complex

• Reconstitution Studies:

  • Incorporation into liposomes with other ATP synthase components

  • Measurement of proton translocation in reconstituted systems

  • ATP synthesis/hydrolysis assays in reconstituted complexes

• Comparative Analysis:

  • Side-by-side comparison with atpF from model organisms

  • Temperature-dependent functional assays

  • Structural comparison with predicted models

• Thermal Stability:

  • Differential scanning calorimetry or thermal shift assays

  • Activity retention after temperature challenges

  • Monitoring of secondary structure changes with temperature using CD spectroscopy