Recombinant Yersinia pseudotuberculosis serotype O:3 ATP synthase subunit b (atpF)

How does the bacterial ATP synthase mechanism work?

Bacterial ATP synthases function through a rotary mechanism:

• Protons flow through the membrane-embedded a subunit and the c-ring of the F₀ sector, driven by the proton motive force

• This proton flow causes rotation of the c-ring

• The c-ring is connected to the central stalk (γ and ε subunits), which rotates within the F₁ sector

• The rotating stalk causes conformational changes in the catalytic sites of the F₁ sector (specifically in the β subunits), enabling ATP synthesis from ADP and inorganic phosphate

• The b subunits (atpF) form part of the stator complex that holds the α₃β₃ hexamer stationary while the central stalk rotates

In Bacillus ATP synthase (which shares structural similarities with Yersinia), the transmembrane proton translocation occurs via two offset half-channels formed by subunit a, with the c-ring rotating as protons move through these channels .

What is the relationship between atpF and other ATP synthase subunits?

In bacterial ATP synthase, subunit b (atpF) forms critical interactions with several other components:

• Interaction with subunit a: The single N-terminal membrane-embedded α-helix in each of the two copies of subunit b forms different interactions with subunit a. One copy interacts with transmembrane α-helices 1, 2, 3, and 4 of subunit a, while the other interacts with α-helices 5 and 6 and the loop between α-helices 3 and 4 .

• Interaction with δ subunit: The C-terminal region of subunit b interacts with the δ subunit of the F₁ sector, forming part of the peripheral stalk.

• Interaction with α subunit: The upper portion of the peripheral stalk connects to the top of the F₁ sector, specifically to the non-catalytic α subunits.

These interactions are essential for coupling the proton flow through F₀ with ATP synthesis in F₁ .

What expression systems are optimal for producing functional recombinant atpF?

For recombinant expression of Y. pseudotuberculosis atpF, E. coli is the most commonly used host system. Key considerations for optimal expression include:

• Expression vector selection: Vectors with strong inducible promoters (T7, tac) and appropriate fusion tags (His-tag) facilitate controlled expression and purification.

• Host strain optimization: E. coli BL21(DE3) and its derivatives are preferred for membrane protein expression due to reduced protease activity .

• Expression conditions: Lower temperatures (16-25°C) and reduced inducer concentrations often improve the yield of properly folded membrane proteins.

• Membrane extraction strategies: Efficient solubilization with appropriate detergents (DDM, LDAO) is critical for extracting functional membrane proteins.

The current recombinant Y. pseudotuberculosis serotype O:3 atpF is expressed in E. coli with an N-terminal His-tag, which facilitates purification while maintaining protein function .

What purification challenges are specific to atpF and how can they be addressed?

Purification of membrane proteins like atpF presents several challenges:

• Membrane extraction efficiency:

  • Challenge: Incomplete solubilization from membranes

  • Solution: Optimization of detergent type, concentration, and extraction time; screening different detergents (DDM, LDAO, OG) at varying concentrations

• Maintaining native conformation:

  • Challenge: Loss of structural integrity during purification

  • Solution: Addition of lipids during purification; use of milder detergents; purification at 4°C

• Aggregation during concentration:

  • Challenge: Protein precipitation at higher concentrations

  • Solution: Use of stabilizing additives such as glycerol (5-10%); maintaining detergent above critical micelle concentration

• Yield limitations:

  • Challenge: Low expression levels common with membrane proteins

  • Solution: Scale-up of culture volume; optimization of induction parameters; use of specialized strains like C41/C43(DE3)

The current protocol for His-tagged Y. pseudotuberculosis atpF utilizes Ni-NTA affinity chromatography followed by buffer exchange into a stabilizing formulation containing 6% trehalose at pH 8.0, which helps maintain protein stability .

How do mutations in atpF affect ATP synthase assembly and function?

Mutations in atpF can have profound effects on ATP synthase structure and function:

• Transmembrane domain mutations:

  • Mutations in the N-terminal transmembrane helix can disrupt proper membrane anchoring and association with subunit a

  • Research demonstrates that mutations in this region are often detrimental to assembly and activity of the complex

• Dimerization interface mutations:

  • Mutations affecting the dimerization of b subunits can destabilize the peripheral stalk

  • These mutations typically result in uncoupled ATP hydrolysis and impaired ATP synthesis

• δ-subunit interaction region mutations:

  • Mutations in the C-terminal region that interacts with the δ subunit can disconnect the F₁ and F₀ sectors

  • This results in functional F₁-ATPase that can hydrolyze ATP but cannot synthesize ATP using the proton gradient

Interestingly, cross-linking experiments have suggested that the N-termini of the two copies of subunit b are in close proximity, but structural data from Bacillus PS3 ATP synthase shows the transmembrane α-helices of the b-subunits on opposite sides of subunit a, suggesting that previously observed cross-linking results may be due to non-specific interactions between b-subunits from neighboring ATP synthases .

What techniques are most effective for studying atpF structure-function relationships?

Several complementary techniques have proven valuable for investigating atpF structure-function relationships:

• Cryo-electron microscopy (cryo-EM):

  • Advantages: Can resolve intact ATP synthase complexes, revealing subunit interactions in native-like environments

  • Example: Cryo-EM of bacterial ATP synthases has revealed the architecture of the membrane region and how the simple bacterial ATP synthase performs the same core functions as more complex mitochondrial enzymes

• X-ray crystallography:

  • Best for: High-resolution structural information of individual domains or subcomplexes

  • Application: Has been used successfully to determine structures of various ATP synthase components

• Small-angle X-ray scattering (SAXS):

  • Benefit: Provides information about protein conformation in solution

  • Application: Can reveal flexibility around interfaces, as demonstrated in studies of thiol peroxidase (Tpx) from Y. pseudotuberculosis

• Site-directed mutagenesis coupled with functional assays:

  • Approach: Systematic mutation of key residues followed by ATP synthesis/hydrolysis activity measurements

  • Outcome: Identifies critical residues for function, assembly, or interaction with other subunits

• Cross-linking mass spectrometry:

  • Method: Chemical cross-linking followed by mass spectrometry analysis

  • Value: Maps protein-protein interactions and proximity relationships within the complex

The combination of these techniques provides a comprehensive understanding of how atpF contributes to ATP synthase structure and function.

How does atpF contribute to Y. pseudotuberculosis metabolism and stress responses?

ATP synthase is central to Y. pseudotuberculosis bioenergetics, with atpF playing several key roles:

• Energy metabolism:

  • As part of ATP synthase, atpF is essential for oxidative phosphorylation and ATP production

  • The ATP synthase complex represents a critical node between respiratory electron transport and cellular energy utilization

• pH homeostasis:

  • Under certain conditions, ATP synthase can work in reverse, hydrolyzing ATP to pump protons and maintain intracellular pH

  • This function may be particularly important during acid stress encountered in the host gastrointestinal tract

• Adaptation to environmental stresses:

  • ATP synthase expression changes in response to various stresses, including temperature shifts and nutrient limitation

  • In Y. pseudotuberculosis, RpoN (σ54) has been shown to regulate the Type III secretion system (T3SS), which is essential for virulence

  • The adaptation to environmental stresses often involves metabolic reprogramming, in which ATP synthase plays a crucial role

• Carbon metabolism regulation:

  • ATP synthase activity is integrated with central carbon metabolism

  • The pyruvate-TCA cycle node has been identified as a focal point for controlling host colonization and virulence of Yersinia

  • This metabolic control is likely coordinated with ATP synthase function to balance energy production with biosynthetic needs

What is the relationship between ATP synthase and antimicrobial tolerance in Yersinia species?

ATP synthase function intersects with antimicrobial tolerance in several important ways:

• Membrane potential maintenance:

  • ATP synthase activity influences bacterial membrane potential

  • Many antibiotics, particularly those targeting protein synthesis, require proper membrane potential for uptake

  • Alterations in ATP synthase activity can therefore affect antibiotic susceptibility

• Metabolic state and antibiotic efficacy:

  • The metabolic state of bacteria, partly determined by ATP synthase activity, affects susceptibility to many antibiotics

  • Genome-wide assessment of antimicrobial tolerance in Y. pseudotuberculosis has shown that multiple genes involved in regulating DNA replication and repair are central to enabling tolerance to antibiotics like ciprofloxacin

• Cell envelope stress responses:

  • ATP synthase function influences bacterial energetics during envelope stress

  • The Cpx envelope stress system in Y. pseudotuberculosis detects cell envelope damage and upregulates factors designed to repair and restore cell envelope integrity while down-regulating virulence factors

  • This stress response system may interact with energy metabolism pathways involving ATP synthase

• Persistence mechanism:

  • Reduced ATP synthase activity is associated with persister cell formation in some bacteria

  • These metabolically quiescent states can contribute to antibiotic tolerance and recalcitrant infections

How does atpF function relate to Y. pseudotuberculosis virulence mechanisms?

While atpF itself is not a direct virulence factor, ATP synthase function intersects with Y. pseudotuberculosis pathogenesis in several ways:

• Energy for virulence factor expression:

  • ATP produced by ATP synthase provides energy for synthesis and operation of virulence factors

  • The Type III secretion system (T3SS), a key virulence mechanism in Y. pseudotuberculosis, requires ATP for assembly and function

• Metabolic adaptation during infection:

  • During infection, Y. pseudotuberculosis undergoes significant metabolic reprogramming

  • ATP synthase regulation is likely part of this adaptation to the host environment

  • The pyruvate-TCA cycle node has been identified as a focal point for controlling host colonization and virulence, with regulatory proteins like Crp and CsrA coordinating the expression of virulence-associated traits with central metabolism

• Response to host-derived antimicrobial factors:

  • Y. pseudotuberculosis must respond to various host defense mechanisms, including oxidative stress

  • Thiol peroxidase (Tpx) from Y. pseudotuberculosis has been characterized as an important protein involved in defense against oxidative stress

  • Energy production through ATP synthase may support these defense mechanisms

• LPS biosynthesis and envelope integrity:

  • ATP synthase provides energy for maintaining cell envelope integrity, including LPS biosynthesis

  • RfaH is essential for virulence and adaptive responses in Y. pseudotuberculosis, regulating the O-antigen biosynthesis operon

  • Defects in ATP production could potentially impact these processes

Can atpF or other ATP synthase components serve as targets for anti-Yersinia therapeutics?

ATP synthase represents a potential therapeutic target based on several considerations:

• Essential function:

  • ATP synthase is critical for bacterial energy metabolism

  • Inhibition would severely compromise bacterial survival and virulence

• Structural differences from host ATP synthase:

  • Bacterial F-type ATP synthases differ structurally from mammalian mitochondrial ATP synthases

  • These differences could potentially be exploited for selective targeting

• Existing precedent:

  • The antimicrobial bedaquiline targets mycobacterial ATP synthase and is used clinically against tuberculosis

  • This demonstrates that ATP synthase can be a viable therapeutic target

• Potential approaches for targeting:

  Targeting Strategy	Mechanism	Advantages	Challenges
  Small molecule inhibitors	Direct binding to ATP synthase components	Potential high specificity	Identifying selective compounds
  Peptide inhibitors	Disruption of subunit interactions	Can target protein-protein interfaces	Delivery into bacteria
  Structure-based design	Rational design based on atpF structure	Highly specific inhibition	Requires detailed structural data
  Combination therapy	ATP synthase inhibitors with conventional antibiotics	Enhanced efficacy, reduced resistance	Complex drug interactions

• Experimental considerations:

  • Recombinant atpF protein can be used in high-throughput screening assays to identify potential inhibitors

  • Structural studies of Y. pseudotuberculosis ATP synthase components would facilitate structure-based drug design

  • Whole-cell assays would be needed to confirm the ability of compounds to penetrate the bacterial envelope and inhibit ATP synthase function

What methods can be used to study the dynamics of ATP synthase in Y. pseudotuberculosis?

Investigating the dynamic aspects of ATP synthase function requires specialized techniques:

• Single-molecule FRET:

  • Application: Measures distances between fluorescently labeled subunits during operation

  • Insight: Reveals conformational changes during the catalytic cycle

  • Example: Similar approaches have shown that the central stalk (subunits γ and ε in bacteria) is responsible for transient storage of torsional energy in rotary ATPases

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS):

  • Method: Measures the rate of hydrogen-deuterium exchange in different protein regions

  • Value: Identifies flexible regions and conformational changes

  • Relevance: Can reveal how atpF interacts with other subunits during the catalytic cycle

• Cryo-electron tomography:

  • Technique: Visualizes macromolecular complexes in their native cellular environment

  • Benefit: Provides insights into the organization and distribution of ATP synthase in the bacterial membrane

  • Context: Has been used to study supramolecular organization of ATP synthases in various organisms

• Site-specific incorporation of unnatural amino acids:

  • Approach: Introduces spectroscopic probes at specific positions within atpF

  • Advantage: Allows precise monitoring of local structural changes

  • Application: Can be used to track conformational changes during ATP synthesis or in response to inhibitors

• Time-resolved structural methods:

  • Implementation: Combines rapid mixing or triggering with structural techniques

  • Insight: Captures transient states during ATP synthase operation

  • Relevance: Could reveal how the b subunits accommodate structural changes during c-ring rotation

Studies with the Bacillus PS3 ATP synthase have shown that the C-terminal water-soluble part of subunit b displays significant conformational variability between rotational states, suggesting its importance in the mechanism of ATP synthesis .

How can researchers investigate the interaction between ATP synthase and the bacterial membrane environment?

The interaction between ATP synthase and the membrane environment can be studied using several approaches:

• Nanodiscs and liposome reconstitution:

  • Method: Reconstituting purified ATP synthase into defined lipid environments

  • Value: Allows study of lipid composition effects on ATP synthase function

  • Application: Measuring ATP synthesis activity in controlled membrane environments

• Native mass spectrometry:

  • Technique: Analyzes intact membrane protein complexes with associated lipids

  • Insight: Identifies specific lipids that co-purify with ATP synthase

  • Relevance: May reveal lipids essential for proper function or assembly

• Molecular dynamics simulations:

  • Approach: Computational modeling of ATP synthase in membranes

  • Benefit: Provides atomic-level insights into protein-lipid interactions

  • Example: Can predict how membrane properties affect proton translocation through the F₀ sector

• Fluorescence microscopy with lipid probes:

  • Method: Combines protein and lipid fluorescent labeling

  • Value: Reveals colocalization and potential lipid domain association

  • Application: Can show how ATP synthase distribution relates to membrane organization

• Site-specific spin labeling:

  • Technique: Introduces spin labels at specific positions in atpF

  • Insight: Measures local mobility and accessibility in the membrane

  • Relevance: Can map the membrane-embedded portions of the protein

These approaches are particularly relevant for understanding how the membrane environment influences ATP synthase function, which could have implications for developing membrane-targeting antimicrobials against Y. pseudotuberculosis.