Recombinant Chlamydia trachomatis V-type ATP synthase subunit I (atpI)
Description
Introduction to Recombinant Chlamydia trachomatis V-type ATP synthase subunit I (atpI)
Recombinant Chlamydia trachomatis V-type ATP synthase subunit I (atpI) is a laboratory-produced version of a natural protein found in the bacterium Chlamydia trachomatis. The atpI protein functions as a critical component of the V-type ATP synthase complex, which is a membrane-associated macromolecular assembly that couples the transfer of protons or sodium cations across membranes with the synthesis or hydrolysis of ATP . This energy conversion machinery is essential for the survival and proliferation of Chlamydia trachomatis, an obligate intracellular bacterial pathogen responsible for numerous human diseases, including sexually transmitted infections.
Function and Role in Chlamydia Metabolism
The V-type ATP synthase complex, of which atpI is a key component, plays a fundamental role in energy metabolism within Chlamydia trachomatis. This complex functions primarily to couple ion gradients with ATP synthesis or hydrolysis, providing the bacterium with mechanisms to maintain energy homeostasis . During ATP synthesis, the complex harnesses the energy from proton or sodium ion gradients across the membrane to catalyze the formation of ATP from ADP and inorganic phosphate.
The presence of a functional V-type ATP synthase suggests that Chlamydia trachomatis can modulate its internal ATP levels through mechanisms beyond direct host ATP uptake. This capability is particularly significant during different phases of the chlamydial developmental cycle, which involves transitions between metabolically active reticulate bodies and dormant, infectious elementary bodies.
Research has shown that during the initial phase of host cell infection, Chlamydia trachomatis cells derive the ATP required for metabolism primarily through ADP/ATP exchange with the host . As infection progresses, the bacterium increasingly relies on its own ATP production mechanisms, including those involving the V-type ATP synthase complex of which atpI is a critical part.
Expression and Regulation
The gene encoding atpI (CT_305) is part of a co-transcribed operon that includes genes for other V-type ATP synthase subunits (K, I, B, D, A, and E) . This co-transcription suggests coordinated regulation of the entire ATP synthase complex, which is logical given that all components must be present in appropriate stoichiometric ratios for proper assembly and function.
Recent transcriptomic analyses have provided insights into the expression patterns of atpI during the chlamydial developmental cycle. Research indicates that over 70% of the Chlamydia trachomatis genome becomes activated within the first hour of infection, including genes related to energy metabolism such as atpI . This early activation underscores the importance of establishing energy metabolism systems promptly after infection.
During active infection, atpI and other genes encoding components of the V-type ATP synthase are expressed to support the energy requirements of rapidly dividing reticulate bodies. In contrast, during persistent infection—a state characterized by altered metabolism and developmental arrest—the expression pattern changes significantly. Studies have shown that genes involved in glycolysis and the pentose phosphate pathway are attenuated during persistence, while genes encoding ADP/ATP exchange proteins and components of the TCA cycle and electron transport system, including those related to the V-type ATP synthase, continue to be expressed .
Recombinant Production and Purification
Recombinant Chlamydia trachomatis V-type ATP synthase subunit I is typically produced in Escherichia coli expression systems . The gene encoding atpI is cloned into a suitable expression vector, often with an N-terminal histidine tag to facilitate purification. Following transformation into E. coli, the bacteria are cultured under conditions that induce expression of the recombinant protein.
After expression, the recombinant atpI protein is isolated from bacterial cells through a series of purification steps. The histidine tag allows for efficient purification using immobilized metal affinity chromatography. The purified recombinant atpI protein is typically provided in a lyophilized powder form for stability during storage and shipping .
The specifications for commercially available recombinant atpI protein are detailed in the following table:
| Parameter | Specification |
|---|---|
| Species | Chlamydia trachomatis |
| Expression System | E. coli |
| Tag | N-terminal His-tag |
| Protein Length | Full Length (1-649 amino acids) |
| Form | Lyophilized powder |
| Storage Conditions | -20°C/-80°C |
| Reconstitution | Deionized sterile water (0.1-1.0 mg/mL) |
| Storage Buffer | Tris/PBS-based buffer, 6% Trehalose, pH 8.0 |
| Recommended Additive | 5-50% glycerol for long-term storage |
| Purity | >90% as determined by SDS-PAGE |
Proper handling and storage of recombinant atpI are crucial for maintaining its structural integrity and functional properties. Repeated freeze-thaw cycles should be avoided, and working aliquots can be stored at 4°C for up to one week .
Research Applications
Recombinant Chlamydia trachomatis V-type ATP synthase subunit I has several important research applications in the fields of microbiology, biochemistry, and immunology. These applications leverage the availability of purified protein to advance our understanding of chlamydial biology and pathogenesis.
Immunological Studies and Vaccine Development
Components of the V-type ATP synthase complex have shown potential as vaccine candidates against chlamydial infections. Research has demonstrated that immunization with subunit A of the V-type ATP synthase (TC0582) provided partial protection against Chlamydia muridarum infection in mice . Given that atpI is part of the same complex and is co-expressed with subunit A, it represents a potential target for vaccine development.
Drug Discovery
The V-type ATP synthase complex, including the atpI subunit, represents a potential target for novel antimicrobial agents against Chlamydia trachomatis. Recombinant atpI can be used in screening assays to identify compounds that inhibit its function or disrupt its interactions with other components of the ATP synthase complex. Such inhibitors could potentially be developed into new antibiotics for the treatment of chlamydial infections.
Differential Expression During Infection Phases
Understanding the expression patterns of atpI during different phases of infection provides valuable insights into chlamydial adaptation strategies. During active infection, Chlamydia trachomatis expresses genes involved in glycolysis and the pentose phosphate pathway, supplementing host-derived ATP with bacterially produced ATP . In this phase, the V-type ATP synthase complex, including atpI, contributes to the bacterium's energy metabolism.
During persistent infection, a state that may contribute to chronic disease, the expression profile changes significantly. In this state, host-derived ATP appears to be the primary energy source, rather than bacterially produced ATP . The metabolic rate in persistent Chlamydia trachomatis is lower than in actively growing cells, as determined by assessments of relative chlamydial primary rRNA transcript levels .
This differential expression of energy metabolism genes, including those encoding the V-type ATP synthase complex, reflects the bacterium's remarkable ability to adapt to changing host environments. For the atpI subunit specifically, its continued expression during persistence suggests its importance in maintaining essential energy functions even during this altered metabolic state.
Potential as a Therapeutic Target
The V-type ATP synthase complex, including the atpI subunit, represents a promising target for therapeutic intervention against Chlamydia trachomatis infections for several reasons:
As a component of the energy metabolism machinery, the V-type ATP synthase is likely essential for the survival and replication of Chlamydia trachomatis. Inhibiting its function could therefore have a detrimental effect on bacterial viability. Additionally, the V-type ATP synthase of Chlamydia trachomatis has unique features that distinguish it from the ATP synthases of human host cells. These differences could potentially be exploited to develop selective inhibitors that target the bacterial enzyme without affecting host cell function.
The membrane location of atpI may make it accessible to drugs or antibodies, creating opportunities for therapeutic agents that cannot penetrate the bacterial cell. Furthermore, the immunogenic properties of V-type ATP synthase components suggest their potential utility in vaccine development strategies.
Product Specs
Note: While we prioritize shipping the format currently in stock, please specify your format preference during order placement for customized preparation.
Note: Our proteins are shipped with standard blue ice packs. Dry ice shipping requires prior arrangement and incurs additional charges.
The tag type is determined during production. If you require a specific tag, please inform us, and we will prioritize its development.
Target Background
KEGG: ctr:CT_305
Q&A
What is the functional role of AtpI in Chlamydia trachomatis?
AtpI functions as a chaperone-like protein involved in the assembly of ATP synthase complexes in Chlamydia trachomatis. While the precise mechanisms remain under investigation, comparative studies with homologous proteins suggest AtpI plays a crucial role in c-ring oligomer formation during assembly of the ATP synthase complex . Unlike in some other bacterial species where AtpI is absolutely required for ATP synthase function, studies with related bacterial systems indicate that AtpI may enhance ATP synthase assembly efficiency without being strictly essential for basic functionality . In Chlamydia, the V-type ATP synthase complex is a multi-subunit assembly that couples ion transfer across membranes with ATP synthesis or hydrolysis, making it vital for energy metabolism in this obligate intracellular pathogen .
How does the structure of Chlamydia trachomatis AtpI compare with AtpI proteins from other bacterial species?
Chlamydia trachomatis AtpI shares significant structural features with homologous proteins from other bacterial species, particularly those encoding V-type ATPases. Computational modeling approaches have revealed that Chlamydial AtpI contains membrane-spanning domains typical of its function in ATP synthase assembly. Sequence alignment studies show that while C. trachomatis AtpI maintains the core functional domains necessary for its chaperone activities, it possesses unique sequence variations that may reflect adaptations to Chlamydia's obligate intracellular lifestyle . These structural differences potentially impact protein-protein interactions within the ATP synthase complex, particularly in the context of Chlamydia's specialized developmental cycle.
What expression systems are most effective for producing recombinant C. trachomatis AtpI?
For recombinant expression of C. trachomatis AtpI, E. coli-based systems using pET vectors have demonstrated reasonable success. When expressing membrane proteins like AtpI, several methodological considerations are critical:
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Codon optimization for the expression host is essential due to the differences in codon usage between Chlamydia and common expression hosts
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Addition of affinity tags (such as 6×His) at the C-terminus rather than N-terminus typically preserves protein functionality
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Expression at lower temperatures (16-20°C) after induction reduces inclusion body formation
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Use of speciality E. coli strains (such as C41(DE3) or C43(DE3)) designed for membrane protein expression improves yield
The PURE system, a reconstituted in vitro protein synthesis system, has also been employed for expression of related ATP synthase components, allowing for direct insertion into phospholipid vesicles for functional studies .
| Expression System | Advantages | Limitations | Yield (mg/L culture) |
|---|---|---|---|
| pET/BL21(DE3) | Widely available, economical | Inclusion body formation | 0.5-1.0 |
| pET/C41(DE3) | Reduced toxicity, better folding | Higher cost | 1.0-2.5 |
| PURE system | Direct incorporation into membranes | Expensive, lower yield | 0.1-0.3 |
| Insect cell system | Better post-translational processing | Complex setup, costly | 1.5-3.0 |
What are the optimal conditions for assessing AtpI-facilitated assembly of the ATP synthase c-ring in vitro?
Reconstitution of AtpI-facilitated ATP synthase c-ring assembly requires careful experimental design. Based on comparable systems, the following methodological approach is recommended:
The in vitro assembly system should incorporate purified recombinant AtpI and c-subunit proteins in the presence of appropriate phospholipids. For optimal results, crude soybean phosphatidylcholine preparations have been successfully used to reconstitute related ATP synthase components in an active form . The assembly reaction should be conducted in a buffer system maintaining pH 7.0-7.5 with 100-150 mM potassium chloride and 5 mM magnesium chloride.
Detection of successful c-ring formation can be accomplished through a combination of:
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Blue native PAGE followed by Western blotting
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Size exclusion chromatography to separate assembled c-rings from monomers
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Electron microscopy to visualize ring structures
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TCA treatment of samples to distinguish between monomeric and oligomeric forms
Research has shown that even in systems where AtpI is known to facilitate assembly, detection of c-ring formation can be technically challenging and may require optimization of detergent types and concentrations during purification and analysis steps .
How can researchers differentiate between direct and indirect effects of AtpI on ATP synthase assembly in Chlamydia?
Distinguishing direct from indirect effects of AtpI on ATP synthase assembly requires a multi-faceted experimental approach:
These approaches collectively can help delineate the specific role of AtpI in ATP synthase assembly, distinguishing between direct chaperoning of c-subunit oligomerization and broader effects on membrane protein biogenesis.
What strategies can overcome the challenges in studying protein-protein interactions involving membrane proteins like AtpI?
Investigating protein-protein interactions involving membrane proteins like AtpI presents unique challenges due to their hydrophobic nature. Advanced methodological approaches include:
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Membrane-based yeast two-hybrid systems: Unlike conventional Y2H, membrane-based systems allow for interaction detection in the context of a lipid bilayer.
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Bimolecular fluorescence complementation (BiFC): Split fluorescent proteins fused to potential interaction partners can verify interactions in live bacterial or eukaryotic cells.
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Microscale thermophoresis (MST): This technique can measure interactions between membrane proteins in detergent micelles with minimal sample consumption.
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Native mass spectrometry: Emerging techniques in native MS allow for analysis of intact membrane protein complexes in detergent micelles or nanodiscs.
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Nanodiscs and proteoliposomes: Reconstituting AtpI and potential interacting partners in defined lipid environments enables controlled interaction studies outside cellular contexts.
These techniques collectively provide complementary information about the interaction network of AtpI within the ATP synthase assembly pathway, particularly important given the challenges of working with Chlamydia as an obligate intracellular pathogen.
How do researchers reconcile conflicting data regarding the essentiality of AtpI for ATP synthase assembly?
The scientific literature presents conflicting evidence regarding whether AtpI is absolutely required for ATP synthase assembly. This discrepancy can be addressed through several analytical approaches:
These contradictions may be reconciled by considering:
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Energy coupling mode: Na+-coupled versus H+-coupled ATP synthases may have different requirements for assembly factors
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Expression levels: High-level expression from multicopy plasmids might artificially bypass AtpI requirements observed under physiological conditions
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Functional redundancy: Overlapping functions between AtpI and YidC/OxaI/Alb3 family proteins may mask phenotypes in single deletion mutants
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Experimental system variations: In vitro versus in vivo assembly systems present different constraints
For Chlamydia trachomatis specifically, the obligate intracellular lifestyle and specialized development cycle may impose unique requirements for ATP synthase assembly that differ from model systems. Researchers should address these contradictions through conditional depletion approaches rather than relying solely on complete knockout studies.
What technical limitations affect our understanding of AtpI function in Chlamydia trachomatis specifically?
Research on AtpI function in C. trachomatis faces several significant technical limitations:
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Genetic manipulation challenges: The obligate intracellular lifestyle of Chlamydia has historically limited genetic manipulation, making traditional approaches like gene deletion/complementation technically difficult.
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Developmental complexity: Chlamydia transitions between metabolically active reticulate bodies and dormant elementary bodies, with potentially different requirements for ATP synthase function at different developmental stages.
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Host-pathogen interactions: Host cell environments may influence ATP synthase assembly and function, creating experimental variables difficult to control.
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Protein purification challenges: Membrane proteins like AtpI are notoriously difficult to purify in their native conformation, particularly from obligate intracellular organisms.
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Heterologous expression limitations: Expression of Chlamydial proteins in surrogate systems may not fully recapitulate native protein interactions and functions.
Recent advances in Chlamydial genetics, including transformation and CRISPR-based approaches, offer promising avenues to overcome some of these limitations. Additionally, sophisticated microscopy techniques like super-resolution imaging coupled with proximity labeling approaches may help elucidate AtpI localization and interaction partners in the native context.
How does understanding AtpI function contribute to vaccine development strategies against Chlamydia trachomatis?
Understanding AtpI function has significant implications for vaccine development against Chlamydia trachomatis:
Recent research has demonstrated that V-type ATP synthase components from Chlamydia can elicit protective immune responses. Specifically, subunit A of the V-type ATP synthase (TC0582) was shown to be immunodominant and provided significant protection against chlamydial challenge in mouse models . Similarly, a newly identified subunit (TC0583) was investigated for its potential to enhance the partial protection provided by subunit A alone .
AtpI, as a component of the same enzymatic complex, represents a potential vaccine candidate that warrants investigation. Several aspects make AtpI particularly interesting from a vaccine development perspective:
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Membrane association: As a membrane-associated protein, AtpI may be accessible to antibodies during certain stages of the Chlamydial developmental cycle.
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Functional importance: If AtpI proves essential for ATP synthase assembly in Chlamydia, antibodies interfering with its function could disrupt bacterial energy metabolism.
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Antigenic conservation: Analysis of sequence conservation across Chlamydial strains could identify conserved epitopes in AtpI suitable for broad-spectrum vaccine development.
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Subunit combination approach: Similar to studies examining TC0582 and TC0583 in combination, AtpI could potentially enhance protection when combined with other ATP synthase components in a multi-subunit vaccine formulation.
Methodologically, researchers should consider both B-cell and T-cell epitope mapping of AtpI to identify regions that might elicit protective immunity without triggering immunopathology, which remains a concern in Chlamydia vaccine development.
What implications does AtpI research have for understanding the evolution of ATP synthases across bacterial species?
Research on Chlamydial AtpI provides valuable insights into the evolution of ATP synthases and their assembly pathways:
The V-type ATP synthase in Chlamydia represents an interesting evolutionary case, as most bacteria possess F-type ATP synthases. Comparative genomic analysis reveals that Chlamydia encode several proteins with high sequence similarity to various subunits of bacterial V-type ATPase complexes . This suggests either horizontal gene transfer or retention of an ancient enzyme complex.
AtpI research contributes to our understanding of:
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Evolutionary conservation of assembly pathways: The variable dependence on AtpI across bacterial species suggests evolutionary plasticity in assembly mechanisms.
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Co-evolution of interacting proteins: Analysis of AtpI and c-subunit sequences across species can reveal co-evolutionary patterns indicative of conserved interaction interfaces.
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Adaptation to specialized niches: Chlamydia's intracellular lifestyle may have driven unique adaptations in its ATP synthase components, including AtpI.
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Functional redundancy development: The relationship between AtpI and YidC family proteins illustrates how parallel or overlapping assembly pathways might have evolved.
These evolutionary insights extend beyond academic interest, potentially informing the development of species-specific ATP synthase inhibitors as novel antimicrobials with narrow spectrum activity.
What are the optimal purification strategies for maintaining structural integrity of recombinant C. trachomatis AtpI?
Purification of recombinant C. trachomatis AtpI requires careful attention to maintain its structural integrity:
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Detergent selection:
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Primary extraction: n-Dodecyl β-D-maltoside (DDM) at 1-1.5% (w/v)
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Purification buffers: 0.05-0.1% DDM or 0.01-0.03% lauryl maltose neopentyl glycol (LMNG)
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Buffer composition:
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Base buffer: 50 mM Tris-HCl or HEPES, pH 7.5-8.0
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Salt: 150-300 mM NaCl (optimize empirically)
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Glycerol: 5-10% to enhance stability
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Reducing agent: 1-5 mM DTT or 0.5-2 mM TCEP
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Purification workflow:
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Immobilized metal affinity chromatography (IMAC) using C-terminal His-tag
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Size exclusion chromatography to separate monomeric from oligomeric forms
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Optional ion exchange step if higher purity is required
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Critical considerations:
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Maintain samples at 4°C throughout purification
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Include protease inhibitors in all buffers
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Consider stabilization through addition of lipids (0.01-0.05 mg/ml) in purification buffers
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Avoid freeze-thaw cycles; store at -80°C in single-use aliquots
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The table below summarizes the effectiveness of different detergents for AtpI purification based on experience with similar membrane proteins:
| Detergent | Extraction Efficiency | Protein Stability | Functional Activity Retention |
|---|---|---|---|
| DDM | +++ | ++ | ++ |
| LMNG | ++ | +++ | +++ |
| Digitonin | + | +++ | +++ |
| CHAPS | ++ | + | + |
| Triton X-100 | +++ | + | + |
How can researchers design experiments to assess the impact of site-directed mutations on AtpI function?
Systematic assessment of structure-function relationships in AtpI through site-directed mutagenesis requires careful experimental design:
This systematic approach can map functional domains within AtpI and potentially identify specific residues essential for c-ring assembly facilitation, providing molecular insights into the chaperone mechanism.
What approaches can differentiate between the roles of AtpI and YidC-family proteins in ATP synthase assembly?
Distinguishing between AtpI and YidC-family protein contributions to ATP synthase assembly requires sophisticated experimental approaches:
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Sequential depletion studies:
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Create conditional depletion systems for both AtpI and YidC proteins
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Analyze ATP synthase assembly during individual and simultaneous depletion
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Monitor accumulation of assembly intermediates under different depletion conditions
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Domain swapping experiments:
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Create chimeric proteins with domains exchanged between AtpI and YidC
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Test functionality of chimeras in appropriate depletion backgrounds
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Identify domains responsible for specific assembly functions
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Temporal assembly analysis:
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Use pulse-chase labeling combined with co-immunoprecipitation
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Determine the sequence of protein interactions during assembly
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Identify whether AtpI and YidC act sequentially or simultaneously
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In vitro reconstitution:
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Purify AtpI, YidC, and ATP synthase components
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Systematically test assembly in defined reconstitution systems
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Vary protein concentrations to identify rate-limiting factors
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Suppressor mutation analysis:
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Select for spontaneous suppressors in AtpI-deficient strains
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Sequence suppressors to identify compensatory mutations
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Determine if YidC upregulation or modification can compensate for AtpI loss
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Based on studies with related systems, there appears to be functional overlap between AtpI and YidC-family proteins, but with specialization for different aspects of ATP synthase assembly or different environmental conditions . In Bacillus species with two YidC homologs (YqjG and SpoIIIJ), functional specialization was observed with different roles at different pH values, suggesting condition-specific functions that might also apply to AtpI .
