Recombinant Acinetobacter sp. ATP synthase subunit a (atpB)

What is the basic structure and composition of Acinetobacter baumannii F1Fo-ATP synthase?

Acinetobacter baumannii F1Fo-ATP synthase (α3:β3:γ:δ:ε:a:b2:c10) is a multi-subunit enzyme complex essential for this strictly respiratory opportunistic human pathogen. The complex consists of two main components:

• The F1 head contains subunits α3β3γδε and is responsible for ATP synthesis/hydrolysis

• The Fo membrane component contains subunits ab2c10 and is involved in proton translocation

Recent cryo-electron microscopy studies have revealed the structure at 3.0 Å resolution, showing unique architectural features compared to other bacterial ATP synthases. Notably, the A. baumannii ATP synthase is incapable of ATP-driven proton translocation due to its latent ATPase activity, which represents an adaptation to prevent wasteful ATP consumption in this pathogen .

How does the a-subunit (atpB) of Acinetobacter ATP synthase differ from that of other bacterial species?

The a-subunit (atpB) in Acinetobacter ATP synthase shows several distinctive structural adaptations:

• N-terminal insertion: A. baumannii has the largest N-terminal insertion among structurally characterized ATP synthases, which repositions the first short α-helix toward the periplasm .

• Proton channel entry site: This shift relocates the entry site of the periplasmic proton channel. While in mammalian ATP synthases protons enter from behind the mini-helix, in A. baumannii they approach from the front as viewed from the c-ring .

• Unique loop extension: Between helices aH4 and aH5 (or aH5 and aH6, depending on numbering system), A. baumannii a-subunit contains a distinctive loop extension formed by predominantly hydrophobic residues plus a charged lysine residue (200PSNPVAKALLIP211) .

• Conservation pattern: This loop extension is conserved within the Acinetobacter genus and Moraxellaceae family but is fully or partially absent in other ATP synthases, making it a potential genus-specific feature .

These structural differences may provide targets for the development of specific inhibitors against Acinetobacter ATP synthase without affecting the host's mitochondrial ATP synthase .

What methodologies are currently used to study the regulation of ATP hydrolysis in Acinetobacter ATP synthase?

Research on ATP hydrolysis regulation in Acinetobacter ATP synthase employs several complementary methodologies:

• Recombinant protein systems: Generation and purification of recombinant A. baumannii F1-ATPase (AbF1-ATPase) composed of subunits α3:β3:γ:ε, allowing study of latent ATP hydrolysis mechanisms .

• ε-free complexes: Creating AbF1-αβγ complexes (without subunit ε) to demonstrate the regulatory role of subunit ε, which showed a 21.5-fold ATP hydrolysis increase, confirming Abε as the major regulator of latent ATP hydrolysis .

• Mutational studies: Single amino acid substitutions within subunit ε or its interacting subunits β and γ, as well as C-terminal truncated mutants of Abε, to identify critical residues for the self-inhibition mechanism .

• Structural analysis:

  • Cryo-EM structure determination (3.0 Å resolution) showing the C-terminal domain of subunit ε (Abε) in an extended position

  • NMR solution structure of the compact form of Abε, revealing interaction between its N-terminal β-barrel and C-terminal α-hairpin domain

• Heterologous expression systems: Using these to explore the importance of Abε's C-terminus in ATP synthesis of inverted membrane vesicles containing AbF1Fo-ATP synthases .

These approaches collectively provide a detailed picture of the regulatory mechanisms controlling ATP hydrolysis in this pathogen .

What are the optimal conditions for expressing and purifying recombinant Acinetobacter ATP synthase subunit a (atpB)?

Based on published protocols for recombinant ATP synthase components from Acinetobacter species, the following approach has been successfully used:

Expression System:

• E. coli is the preferred heterologous host for expression due to ease of culture and genetic manipulation

• Alternative expression systems include yeast, baculovirus, and mammalian cells for specific applications

Expression Vector:

• Plasmids with strong, inducible promoters (pET series vectors are commonly used)

• For membrane proteins like atpB, vectors with fusion tags (His-tag, Avi-tag) facilitate purification

Induction and Growth Conditions:

• Growth at 37°C to an OD600nm of 0.6 in appropriate media (LB or TSB) with necessary antibiotics

• Induction with IPTG (0.05-0.5 mM) for 4-6 hours at moderate shaking (180 rpm)

• For membrane proteins, lower temperatures (16-25°C) during induction may improve folding

Purification Protocol:

• Cell lysis by sonication in buffer containing 50 mM Tris-HCl, 0.1 mM EDTA, 50 mM NaCl, pH 8.0, supplemented with protease inhibitors

• Centrifugation to separate membrane fractions

• For membrane proteins like atpB, detergent solubilization (e.g., dodecyl maltoside)

• Affinity chromatography using appropriate tag (His-tag purification on Ni-NTA resin)

• Ion-exchange chromatography for further purification

• Size exclusion chromatography for final polishing

Storage Conditions:

• For liquid form: -20°C/-80°C with 50% glycerol; shelf life approximately 6 months

• For lyophilized form: -20°C/-80°C; shelf life approximately 12 months

• Avoid repeated freeze-thaw cycles; store working aliquots at 4°C for up to one week

What genetic manipulation techniques are most effective for studying Acinetobacter ATP synthase in vivo?

Several genetic approaches have been successfully employed to study ATP synthase in Acinetobacter species:

• Homologous Recombination:

  • Highly efficient in Acinetobacter species, which naturally exhibit competence for DNA uptake

  • ATP synthase genes in Acinetobacter are located in recombination hotspots, facilitating genetic manipulation

  • The locus containing ATP synthase genes ranks among the top most recombined genes (17th out of 1694 genes)

• Gene Knockout Systems:

  • In-frame replacement with resistance cassettes (e.g., kanamycin resistance cassette aph1 as used for oxyR)

  • Generation of clean deletions using counter-selectable markers

• Heterologous Expression Systems:

  • For functional studies when direct manipulation is challenging

  • Shuttle vectors like pAT801 containing Acinetobacter oriC in E. coli plasmids enable expression in both hosts

  • Expression of Acinetobacter genes in ATP synthase-deficient E. coli strains (e.g., strain QC774(DE3)) for complementation studies

• Site-Directed Mutagenesis:

  • For studying critical residues in ATP synthase subunits

  • Particularly useful for analyzing regulatory domains like the C-terminal domain of subunit ε

• Reporter Gene Fusions:

  • For monitoring expression patterns and regulation

  • qRT-PCR validation of RNA-seq data has been successfully employed to study gene expression changes in Acinetobacter

These approaches have successfully elucidated mechanisms of ATP synthase function, regulation, and potential as antimicrobial targets in Acinetobacter species.

What are the challenges in reconstituting functional Acinetobacter ATP synthase complexes for in vitro studies?

Reconstitution of functional Acinetobacter ATP synthase complexes faces several technical challenges:

• Membrane Protein Stability:

  • The a-subunit (atpB) is highly hydrophobic with multiple transmembrane segments, making it challenging to maintain in a correctly folded state outside the membrane environment

  • Requires careful selection of detergents and lipids to preserve native structure

• Complex Assembly:

  • The complete F1Fo complex (α3:β3:γ:δ:ε:a:b2:c10) involves assembly of multiple subunits in the correct stoichiometry and orientation

  • Intermediate subcomplexes (e.g., F1-ATPase composed of α3:β3:γ:ε) are more tractable for experimental studies

• Maintaining Functionality:

  • Preserving the unique regulatory features, such as the self-inhibition mechanism mediated by subunit ε

  • Ensuring the correct proton-conducting properties of the assembled complex

• Experimental Approaches to Address These Challenges:

  • Inverted membrane vesicles: Preparation of membrane vesicles containing ATP synthase in its native lipid environment

  • Reconstitution into liposomes: Purified components can be reconstituted into artificial liposomes with defined lipid composition

  • Nanodiscs: Incorporation of ATP synthase components into nanodiscs for structural and functional studies

  • Detergent screening: Systematic testing of detergents for optimal extraction while maintaining function

  • Cryo-EM analysis: Direct visualization of the complex structure in different conformational states

These challenges have been partially overcome through the purification of recombinant A. baumannii F1-ATPase and structural characterization by cryo-EM at 3.0 Å resolution, but complete functional reconstitution of the entire F1Fo complex remains challenging .

How does the ε subunit regulate ATP hydrolysis in Acinetobacter ATP synthase, and how does this differ from other bacterial species?

The ε subunit in Acinetobacter baumannii ATP synthase serves as the major regulator of latent ATP hydrolysis through a sophisticated mechanism:

• Structural Basis of Regulation:

  • The C-terminal domain of subunit ε (Abε) can adopt two conformations: an extended "up" position that inhibits ATP hydrolysis and a compact "down" position

  • In the inhibitory "up" position, Abε blocks rotation in the hydrolysis direction while still enabling ATP synthesis, functioning as a unidirectional ratchet

• Key Structural Features:

  • Similar to other bacteria, Abε contains an extended C-terminal α-helix

  • Where Thermus thermophilus (PS3) ε terminates, both A. baumannii and E. coli ε subunits unwind in a short 126AQL128 motif

  • Unlike E. coli ε, which bends horizontally between α- and β-subunits, A. baumannii ε continues upward into the F1 head, forming additional helical turns followed by a five-residue extension

  • This extension forms additional interactions with γ-, βTP-, and αDP-subunits, potentially stabilizing the inhibitory "up" position

• Experimental Evidence:

  • Removal of ε from AbF1-ATPase resulted in a 21.5-fold increase in ATP hydrolysis activity, demonstrating its inhibitory role

  • Mutational studies of single amino acid substitutions and C-terminal truncations identified critical residues for this self-inhibition mechanism

• Species-Specific Differences:

  • Unlike some bacterial homologs, Abε does not bind MgATP, which regulates up/down movements in other bacterial counterparts

  • The ratchet mechanism in A. baumannii is similar to that in Thermus thermophilus (PS3) but distinct from mycobacterial ATP synthase, which relies on temporary β-strand interaction between α- and ε-subunits

This unique regulatory mechanism helps A. baumannii prevent wasteful ATP hydrolysis, supporting its adaptation as a persistent pathogen in host environments .

What structural features of the Acinetobacter ATP synthase make it a potential target for novel antimicrobial development?

Acinetobacter ATP synthase presents several unique structural features that make it an attractive target for selective antimicrobial development:

• Distinctive a-subunit Features:

  • Unique loop extension between transmembrane helices aH4 and aH5 (200PSNPVAKALLIP211) that is conserved in Acinetobacter but absent in human mitochondrial ATP synthase

  • This loop may reach the periplasmic membrane edge and could provide privileged access to small molecules and biologics

  • Repositioned N-terminal mini-helix that alters the proton entry channel compared to mammalian ATP synthases

• a/c-ring Interface Characteristics:

  • Distinctive a/c10 interface that represents a prime target for developing highly specific inhibitors

  • Success of bedaquiline (BDQ) against mycobacterial ATP synthase by targeting this interface suggests similar approaches could work for Acinetobacter

• Self-inhibition Mechanism:

  • The unique arrangement of subunit ε in the inhibitory "up" position

  • Specific interactions between ε and other subunits that are absent in human mitochondrial ATP synthase

• Essential Nature of ATP Synthase:

  • A. baumannii is a strictly respiratory pathogen, making its ATP synthase essential for viability

  • Targeting this enzyme would directly affect the culmination of bioenergetics in this pathogen

• Potential Antimicrobial Development Strategies:

  • Structure-based drug design targeting the a/c10 interface

  • Screening of diarylquinolines (DARQs) derivatives, similar to those used against mycobacteria

  • Development of compounds that interfere with the unique regulatory mechanisms

  • Targeting the distinctive proton entry channel formed by the a-subunit

The high-resolution structural data (3.0 Å cryo-EM) now available for A. baumannii ATP synthase provides a foundation for rational drug design against this challenging multidrug-resistant pathogen .

How do oxidative stress conditions affect ATP synthase expression and function in Acinetobacter species?

Oxidative stress significantly impacts ATP synthase expression and function in Acinetobacter species through several interconnected mechanisms:

• Transcriptional Regulation:

  • OxyR, a key transcriptional regulator in Acinetobacter, activates numerous genes in response to H2O2 exposure

  • RNA sequencing reveals that ATP synthase gene expression is integrated with oxidative stress responses

  • Deletion of oxyR significantly alters the transcriptional response to oxidative stress, potentially affecting energy metabolism

• Energy Metabolism Adaptations:

  • Under oxidative stress, Acinetobacter modulates ATP synthase activity to balance energy production with oxidative damage protection

  • The latent ATPase activity of Acinetobacter ATP synthase prevents wasteful ATP hydrolysis during stress conditions, preserving energy resources

• Protection Mechanisms:

  • Superoxide dismutases (SODs) in Acinetobacter function in different cellular compartments to protect against oxidative damage:

    • SodB (iron SOD) is located in the cytosol

    • SodC (copper/zinc SOD) is found in both periplasm and outer membrane vesicles

  • These compartmentalized SODs protect the ATP synthase complex from oxidative damage

• Correlation with Metabolic Pathways:

  • Oxidative stress response is linked to alterations in:

    • Sulfur homeostasis pathways

    • Iron homeostasis (critical for SOD function)

    • Phosphate transport systems

  • These pathways indirectly influence ATP synthase function by affecting substrate availability and cellular redox state

• Experimental Evidence for Oxidative Stress Adaptation:

  • Genes upregulated under oxidative stress in A. baumannii (partial list from transcriptomic data) :

These adaptive responses help Acinetobacter maintain energy production through ATP synthase while protecting against oxidative damage, contributing to its persistence as a pathogen in hostile host environments .

How has the ATP synthase a-subunit (atpB) evolved among different Acinetobacter species, and what does this tell us about adaptation to different environments?

The ATP synthase a-subunit (atpB) shows significant evolutionary patterns among Acinetobacter species that reflect adaptation to different ecological niches:

• Conservation Within the Genus:

  • The unique loop extension between helices (200PSNPVAKALLIP211) is conserved within the Acinetobacter genus and Moraxellaceae family

  • This conservation suggests functional importance specific to these bacterial groups

  • Sequence alignment reveals high conservation of functional domains while allowing species-specific adaptations in non-catalytic regions

• Horizontal Gene Transfer:

  • ATP synthase genes in Acinetobacter are located in homologous recombination hotspots

  • The atpB gene and adjacent regions show evidence of frequent horizontal transfer across Acinetobacter species

  • When analyzing all Acinetobacter genomes, the ATP synthase locus ranked as the 17th most recombined gene out of 1694 core genes

• Species Identification Value:

  • While not atpB specifically, other genes like rpoB show interspecies polymorphisms but intraspecies conservation

  • This pattern allows for reliable species identification within the Acinetobacter genus

  • The rpoB gene similarities between different Acinetobacter species range from 84.8-95.6%, while intraspecies similarity exceeds 99%

• Adaptation to Environmental Pressures:

  • Clinical isolates show adaptations in ATP synthase that may contribute to:

    • Survival in hospital environments with antimicrobial exposure

    • Resistance to host immune defenses, particularly oxidative stress

    • Efficient energy production in nutrient-limited conditions

  • These adaptations are reflected in the unique structural features of the a-subunit, particularly in the proton channel region

• Implications for Pathogenicity:

  • The evolution of latent ATPase activity in pathogenic Acinetobacter species (preventing wasteful ATP hydrolysis)

  • This feature likely contributes to persistence during infection by conserving energy resources

  • The increased frequency of horizontal gene transfer in clinical settings may accelerate adaptive evolution of ATP synthase genes

This evolutionary pattern suggests that ATP synthase, particularly the a-subunit, has played an important role in the adaptation of Acinetobacter species to diverse environments, including the transition to opportunistic human pathogens .

What experimental approaches are most effective for studying the proton translocation mechanism in Acinetobacter ATP synthase compared to other bacterial species?

Studying proton translocation in Acinetobacter ATP synthase requires specialized approaches due to its unique features:

• Structural Analysis Techniques:

  • Cryo-electron microscopy (cryo-EM): Provides high-resolution (3.0 Å) structures revealing the unique a-subunit features that define proton pathways

  • Comparative modeling: Mapping the distinctive features of Acinetobacter proton channels by comparison with other bacterial and mitochondrial ATP synthases

  • Molecular dynamics simulations: Predicting proton movement through the a-subunit/c-ring interface based on structural data

• Functional Assays:

  • Inverted membrane vesicles (IMVs): Prepared from Acinetobacter to measure ATP synthesis driven by artificial proton gradients

  • Reconstituted liposome systems: Purified ATP synthase components incorporated into artificial membranes to study proton translocation directly

  • pH-sensitive fluorescent probes: To monitor proton movement across membranes containing ATP synthase

  • Patch-clamp electrophysiology: For direct measurement of proton currents through the Fo sector

• Genetic Approaches:

  • Site-directed mutagenesis: Targeting key residues in the proton path, particularly the unique loop region (200PSNPVAKALLIP211) and the repositioned N-terminal mini-helix

  • Chimeric constructs: Creating hybrid ATP synthases with components from different species to isolate the effects of Acinetobacter-specific features

• Unique Considerations for Acinetobacter:

  • The repositioned proton entry channel in A. baumannii (approaching from the front of the mini-helix rather than behind it as in mammalian ATP synthases)

  • The additional loop extension that may influence proton access to the a/c-ring interface

  • The need to account for the latent ATPase activity when studying proton translocation in the reverse direction

• Comparative Approach Benefits:

  • Studying closely related species with different pathogenicity profiles (e.g., A. baumannii vs. non-pathogenic Acinetobacter species)

  • Comparing Acinetobacter ATP synthase with other bacterial ATP synthases that have been well-characterized (E. coli, Mycobacterium) to identify unique features

These experimental approaches collectively provide insights into the distinctive proton translocation mechanism in Acinetobacter ATP synthase, which may inform development of species-specific inhibitors targeting this essential enzyme .

What can the structure of recombinant Acinetobacter ATP synthase components tell us about bacterial adaptation to extreme environments?

The structural features of Acinetobacter ATP synthase components reveal several adaptations to extreme environments:

• Stress Resistance Adaptations:

  • The unique self-inhibition mechanism mediated by subunit ε prevents wasteful ATP hydrolysis during stress conditions

  • This adaptation is critical for survival in nutrient-limited or oxidative stress environments commonly encountered during infection

  • The extended conformation of subunit ε functions as a unidirectional ratchet, allowing ATP synthesis while preventing hydrolysis—an important energy conservation strategy

• Membrane Interface Adaptations:

  • The distinctive loop extension in the a-subunit (200PSNPVAKALLIP211) may interact with membrane lipids through the charged lysine residue (position 206)

  • This feature potentially stabilizes ATP synthase in diverse membrane environments or during membrane stress

  • The repositioned proton entry channel suggests adaptation to different proton concentration gradients or membrane potentials

• Oxidative Stress Resistance:

  • Studies on polyextremophilic Acinetobacter sp. Ver3 (highly tolerant to radiation and pro-oxidants) reveal coordinated expression of ATP synthase with oxidative stress defense systems

  • Superoxide dismutases (SODs) strategically localized in different cellular compartments protect the ATP synthase complex from oxidative damage

  • This coordinated response suggests adaptation to environments with high oxidative stress

• Host Environment Adaptation:

  • Clinical isolates show high serum resistance despite efficient recognition by the complement system

  • The ATP synthase structure contributes to energy production efficiency in the challenging host environment

  • Combined with latent ATPase activity, this enables persistence during infection

• Evolutionary Implications:

  • The frequent horizontal gene transfer of ATP synthase genes among Acinetobacter species suggests rapid adaptation to new environments

  • The conservation of unique structural features within the genus indicates successful adaptation strategies

  • The increased recombination rate at ATP synthase loci compared to the global genome recombination rate (ranking 17th most recombined out of 1694 core genes) suggests strong selective pressure for adaptive variants

These structural adaptations in Acinetobacter ATP synthase contribute to the genus's remarkable ability to thrive in diverse environments, from natural soil and water habitats to the challenging conditions of hospital settings and human hosts .

How can recombinant Acinetobacter ATP synthase subunits be used to screen for novel antimicrobial compounds?

Recombinant Acinetobacter ATP synthase subunits provide valuable tools for antimicrobial discovery through several screening approaches:

• Structure-Based Virtual Screening:

  • High-resolution structures (3.0 Å cryo-EM) of A. baumannii ATP synthase enable in silico screening against specific targets

  • Computational docking of compound libraries to unique binding sites, particularly:

    • The a/c-ring interface (similar to bedaquiline binding site in mycobacteria)

    • The distinctive loop extension in the a-subunit (200PSNPVAKALLIP211)

    • The interface between subunit ε and other F1 components in the inhibitory position

• Biochemical Screening Assays:

  • ATP hydrolysis inhibition: Measuring ATPase activity of purified recombinant F1-ATPase (α3:β3:γ:ε) in the presence of test compounds

  • ATP synthesis assays: Using inverted membrane vesicles containing reconstituted ATP synthase to screen for compounds that block ATP production

  • Proton translocation assays: Fluorescence-based methods to identify compounds that disrupt proton movement through the Fo sector

• Target-Based Approaches:

  • Directed evolution of small molecule binders: Selection of peptides or aptamers that bind specifically to unique regions of Acinetobacter ATP synthase

  • Fragment-based screening: Identifying small molecular fragments that bind to specific pockets, followed by chemical expansion

  • Rational modification of known inhibitors: Using the diarylquinoline (DARQ) scaffold that targets mycobacterial ATP synthase as a starting point for Acinetobacter-specific derivatives

• Whole-Cell Screening with Target Validation:

  • Screening compounds against Acinetobacter cultures followed by:

    • Target validation using resistant mutant generation and sequencing

    • Overexpression of recombinant ATP synthase subunits to confirm the molecular target

    • Competition assays with known ATP synthase ligands

• Methodological Workflow:

  • Initial high-throughput screening → hit identification → target binding confirmation → structure-activity relationship studies → lead optimization

  • Confirmation of selectivity by testing against human mitochondrial ATP synthase to ensure safety

  • Validation in animal infection models to confirm in vivo efficacy against Acinetobacter infections

These approaches leverage the unique structural features of Acinetobacter ATP synthase to identify compounds that could become next-generation therapeutics against multidrug-resistant A. baumannii infections .

What are the current technical challenges in developing ATP synthase inhibitors specific to Acinetobacter species?

The development of Acinetobacter-specific ATP synthase inhibitors faces several significant technical challenges:

• Structural Complexity and Membrane Association:

  • The a-subunit (atpB) is embedded in the membrane with multiple transmembrane segments

  • Difficulty in obtaining stable, functional recombinant protein for high-throughput screening

  • Challenges in creating appropriate assay systems that mimic the native membrane environment

• Selectivity Requirements:

  • Need for compounds that selectively target Acinetobacter ATP synthase over human mitochondrial ATP synthase

  • Difficulty in achieving sufficient selectivity due to the conserved catalytic mechanism

  • Requirement to exploit subtle structural differences in the a-subunit and a/c-ring interface

• Compound Properties:

  • Need for compounds with:

    • Appropriate membrane permeability to reach the target

    • Physicochemical properties suitable for penetration of Acinetobacter's outer membrane

    • Stability against bacterial efflux mechanisms and degradative enzymes

  • These requirements often conflict with properties needed for binding to membrane protein targets

• Resistance Development:

  • High frequency of horizontal gene transfer in Acinetobacter may accelerate resistance development

  • ATP synthase genes in Acinetobacter are located in recombination hotspots, facilitating genetic exchange

  • Need for inhibitors with high binding affinity and multiple binding contacts to reduce resistance potential

• Technical Limitations in Screening Approaches:

  • Difficulties in establishing high-throughput assays for membrane proteins

  • Challenges in reconstituting fully functional ATP synthase complexes for screening

  • Limitations in current structural understanding of dynamic aspects of the enzyme mechanism

• Translational Challenges:

  • Ensuring in vivo efficacy in infection models

  • Addressing pharmacokinetic and toxicological requirements

  • Developing appropriate formulations for clinical application

Despite these challenges, recent structural insights from cryo-EM studies (3.0 Å resolution) and the success of bedaquiline against mycobacterial ATP synthase provide a foundation for rational drug design targeting the unique features of Acinetobacter ATP synthase .

How do antimicrobial resistance mechanisms in Acinetobacter interact with ATP synthase function and expression?

Antimicrobial resistance mechanisms in Acinetobacter have complex interactions with ATP synthase function and expression:

• Energy-Dependent Resistance Mechanisms:

  • Many resistance mechanisms are energy-dependent, requiring ATP generated by ATP synthase:

    • Active efflux pumps (MFS transporters, ABC transporters) that expel antibiotics

    • ATP-binding cassette (ABC) transporters identified in transcriptomic studies

    • These systems increase ATP demand, potentially affecting ATP synthase expression

• Transcriptional Coupling:

  • RNA-seq studies reveal coordinated expression between ATP synthase genes and resistance determinants

  • Upregulation of transport systems during stress conditions parallels changes in energy metabolism

  • Genes identified in transcriptomic studies show coupling between energy production and resistance mechanisms :

• Horizontal Gene Transfer and ATP Synthase:

  • ATP synthase genes are located in recombination hotspots in Acinetobacter genomes

  • The same mechanisms that facilitate transfer of resistance genes can affect ATP synthase

  • A novel subclass of aminoglycoside nucleotidyltransferases, ANT(3")-II, is horizontally transferred among Acinetobacter by the same recombination mechanisms that can affect ATP synthase genes

• Metabolic Adaptations During Resistance:

  • Acquisition of resistance often causes metabolic burden, requiring compensatory changes in energy production

  • ATP synthase expression may be modulated to meet altered energy demands in resistant strains

  • The latent ATPase activity in A. baumannii ATP synthase helps conserve energy in stressed conditions

• Oxidative Stress and Resistance:

  • Antibiotic exposure often induces oxidative stress

  • ATP synthase function is protected by oxidative stress response systems (OxyR regulon, superoxide dismutases)

  • Coordinated expression between stress response and energy production supports resistance mechanisms

• Novel Targets in Resistant Strains:

  • As conventional antibiotics become ineffective due to resistance, ATP synthase emerges as an alternative target

  • The essential nature of ATP synthase in the strictly respiratory A. baumannii makes it an attractive target in multidrug-resistant strains

  • Structural features unique to Acinetobacter ATP synthase provide opportunities for selective inhibition

These interactions highlight the complex relationship between energy metabolism and antimicrobial resistance in Acinetobacter, suggesting that targeting ATP synthase could be effective against multidrug-resistant strains by compromising both energy production and resistance mechanisms .

What emerging technologies could enhance our understanding of Acinetobacter ATP synthase dynamics and function?

Several cutting-edge technologies are poised to revolutionize our understanding of Acinetobacter ATP synthase:

• Time-Resolved Cryo-EM:

  • Capturing intermediate conformational states during the catalytic cycle

  • Visualizing the dynamic transitions between different rotational states of the central stalk

  • Revealing the structural basis of the unidirectional ratchet mechanism mediated by subunit ε

• Single-Molecule Techniques:

  • Single-molecule FRET to monitor conformational changes in real-time

  • Optical or magnetic tweezers to measure rotational torque and step size

  • Nanopore recordings to study proton translocation through individual ATP synthase complexes

• Advanced Computational Methods:

  • Molecular dynamics simulations incorporating longer timescales to model the complete catalytic cycle

  • Quantum mechanics/molecular mechanics (QM/MM) approaches to model proton transfer events

  • Machine learning algorithms to predict functional consequences of structural variations among species

• Integrative Structural Biology:

  • Combining information from cryo-EM, X-ray crystallography, NMR, and mass spectrometry

  • Hydrogen-deuterium exchange mass spectrometry (HDX-MS) to map dynamic regions and ligand binding sites

  • Cross-linking mass spectrometry to identify intersubunit contacts in different functional states

• In-Cell Structural Biology:

  • Cryo-electron tomography of ATP synthase in its native cellular environment

  • In-cell NMR to study conformational changes under physiological conditions

  • Correlative light and electron microscopy to study ATP synthase distribution and dynamics in living Acinetobacter

• Synthetic Biology Approaches:

  • Engineering minimal ATP synthase systems with defined components

  • Creating chimeric enzymes to isolate the contributions of specific structural features

  • Developing optogenetic controls for ATP synthase to manipulate activity with light

• Native Mass Spectrometry:

  • Analyzing intact ATP synthase complexes to determine subunit stoichiometry and stability

  • Identifying post-translational modifications that may regulate activity

  • Studying the binding of small molecule inhibitors to specific subunits

These technologies promise to provide unprecedented insights into the dynamic behavior of Acinetobacter ATP synthase, potentially revealing new targets for antimicrobial development and deepening our understanding of this essential enzyme's function in pathogenic bacteria .

How might advances in structural biology techniques further refine our understanding of Acinetobacter ATP synthase as a drug target?

Recent and future advances in structural biology are significantly enhancing the potential of Acinetobacter ATP synthase as a drug target:

• Higher Resolution Structures:

  • Current cryo-EM structures at 3.0 Å resolution have revealed key features of A. baumannii ATP synthase

  • Pushing resolution limits below 2.0 Å would:

    • Resolve precise side chain orientations in the proton channel

    • Visualize water molecules in the proton pathway

    • Identify subtle conformational changes induced by inhibitor binding

  • This level of detail would enable highly specific structure-based drug design

• Structures with Bound Inhibitors:

  • Co-structures of ATP synthase with lead compounds or fragments

  • Mapping precise binding sites, particularly at the a/c-ring interface

  • Identifying induced conformational changes that might be exploited for drug design

  • Similar to structures of bedaquiline bound to mycobacterial ATP synthase that revealed binding at the a/c-ring interface

• Multi-State Conformational Analysis:

  • Capturing ATP synthase in multiple functional states beyond the current three rotational states

  • Identifying transient pockets that appear only in certain conformations

  • Developing time-resolved structural techniques to visualize the complete catalytic cycle

  • This would enable targeting of specific conformational states with inhibitors

• Integration with Computational Methods:

  • Molecular dynamics simulations based on high-resolution structures

  • Free energy calculations to predict binding affinities of potential inhibitors

  • Machine learning approaches to identify novel binding sites not obvious from static structures

  • These computational insights would accelerate rational drug design

• Structure-Guided Fragment Screening:

  • Using high-throughput crystallography or cryo-EM to screen fragment libraries

  • Identifying multiple small molecule binding sites across the ATP synthase complex

  • Linking fragments that bind to adjacent sites to create high-affinity inhibitors

  • This approach has been successful for other challenging drug targets

• Structure-Activity Relationships:

  • Systematic structural analysis of inhibitor derivatives

  • Correlating structural features with antimicrobial activity

  • Optimizing selectivity by exploiting structural differences between bacterial and human ATP synthases

  • This would guide medicinal chemistry efforts toward more potent and selective compounds

These advances would build upon the current structural understanding of Acinetobacter ATP synthase, potentially leading to novel antimicrobials targeting this essential enzyme in multidrug-resistant A. baumannii .

What interdisciplinary approaches could accelerate the development of ATP synthase-targeted therapeutics against multidrug-resistant Acinetobacter infections?

Accelerating the development of ATP synthase-targeted therapeutics against multidrug-resistant Acinetobacter requires integrating multiple disciplines:

• Structural Biology and Medicinal Chemistry Integration:

  • Rapid iterative cycles between structure determination and compound synthesis

  • Fragment-based drug discovery guided by high-resolution structures

  • Structure-based optimization of lead compounds targeting unique features of Acinetobacter ATP synthase

• Microbiology and Genomics Synergy:

  • Large-scale genomic analysis of clinical isolates to identify ATP synthase variations

  • Correlating genetic polymorphisms with phenotypic resistance patterns

  • Developing rapid techniques to predict susceptibility to ATP synthase inhibitors

  • Understanding horizontal gene transfer patterns that might affect drug target conservation

• Biophysics and Computational Biology Collaboration:

  • Molecular dynamics simulations to predict inhibitor binding and conformational changes

  • Machine learning approaches to identify novel scaffolds with potential activity

  • Quantum mechanical calculations to understand proton translocation mechanisms

  • These computational insights can guide experimental design and compound optimization

• Systems Biology and Metabolomics:

  • Understanding metabolic adaptations in response to ATP synthase inhibition

  • Identifying potential synergistic targets in energy metabolism pathways

  • Developing combination strategies to prevent resistance development

  • Metabolic flux analysis to quantify the impact of ATP synthase inhibition

• Pharmaceutical Sciences and Nanotechnology:

  • Developing specialized delivery systems to overcome Acinetobacter's permeability barriers

  • Nanoparticle formulations targeting bacterial membranes to deliver ATP synthase inhibitors

  • Optimizing pharmacokinetic properties of lead compounds for in vivo efficacy

  • Creating extended-release formulations for chronic or preventive applications

• Clinical Microbiology and Infectious Disease:

  • Establishing standardized susceptibility testing for ATP synthase inhibitors

  • Developing animal models that accurately predict clinical efficacy

  • Designing appropriate clinical trials for hospital-acquired infections

  • Creating strategies for compassionate use in critically ill patients with limited options

• Multi-Target Approach:

  • Combining ATP synthase inhibitors with other novel targets such as:

    • Inhibitors of aminoglycoside nucleotidyltransferases

    • Compounds targeting superoxide dismutases involved in oxidative stress resistance

    • Agents disrupting iron acquisition systems upregulated during infection