Recombinant Rickettsia conorii Ubiquinol-cytochrome c reductase iron-sulfur subunit (petA)
Product Specs
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Target Background
Component of the ubiquinol-cytochrome c reductase complex (complex III or cytochrome bc1 complex), a respiratory chain component essential for generating the electrochemical potential driving ATP synthesis.
KEGG: rco:RC0358
Q&A
What is Rickettsia conorii Ubiquinol-cytochrome c Reductase Iron-Sulfur Subunit (petA)?
Rickettsia conorii Ubiquinol-cytochrome c Reductase Iron-Sulfur Subunit, encoded by the petA gene (also designated RC0358), is a critical component of the bacterial electron transport chain. This protein, also known as the Rieske iron-sulfur protein (RISP), contains 177 amino acids in its full-length form and plays an essential role in energy metabolism within this obligate intracellular pathogen. The protein facilitates electron transfer between ubiquinol and cytochrome c during oxidative phosphorylation, making it crucial for bacterial survival and pathogenicity. The UniProt ID for this protein is Q92IR2 .
The full amino acid sequence is:
MSDTEDNKNKQTTRRDFMVLTASSVAAIGAVCTLWPLVDSLNPSADVLALSSIEVDLSNIAVGQTVTVKWQGKPVFITNRTPDKIAEARAVKMSELIDPEADQARVKAGHDNWLVITIGICTHLGCVPLANQGEYDGWFCPCHGSQYDSSGRVRRGPAPLNLAVPPYTFISDKKIRIG
What are the key structural features of petA protein?
The petA protein contains several critical structural features that determine its function in electron transport:
| Structural Feature | Position/Description | Functional Significance |
|---|---|---|
| Iron-sulfur cluster | Coordinated by conserved cysteine residues | Primary electron acceptance site |
| Transmembrane domain | N-terminal region | Membrane anchoring |
| Soluble domain | C-terminal region | Interaction with other complex components |
| Conserved motifs | CXHXGCX₁₅CPCH | Iron-sulfur cluster binding |
The protein adopts a folded structure where the iron-sulfur cluster is positioned optimally for electron transfer. This arrangement allows efficient electron movement from ubiquinol to the iron-sulfur cluster and subsequently to cytochrome c1, driving energy production in the bacterium. The structure enables the protein to function within the cytochrome bc1 complex (Complex III) of the respiratory chain.
What expression systems yield optimal results for recombinant petA production?
For recombinant expression of Rickettsia conorii petA, E. coli remains the most efficient and widely used heterologous expression system. According to available data, the recombinant protein has been successfully expressed in E. coli with an N-terminal His-tag . The inclusion of the His-tag facilitates purification while maintaining protein functionality.
Recommended expression parameters:
| Parameter | Optimal Condition | Notes |
|---|---|---|
| Expression vector | pET-based vectors | Provides strong T7 promoter control |
| E. coli strain | BL21(DE3) or Rosetta | Rosetta provides rare codons often found in Rickettsia |
| Induction | 0.5-1 mM IPTG | Lower temperatures (16-25°C) improve folding |
| Expression temperature | 16-25°C | Slower expression improves folding |
| Expression duration | 16-20 hours | Extended time compensates for lower temperature |
For researchers requiring functional protein, expression conditions that promote proper iron-sulfur cluster formation should be considered, including supplementation of the growth medium with iron and optimization of oxygen levels during cultivation.
What are the most effective purification strategies for recombinant petA?
Purification of recombinant His-tagged petA protein typically involves a multi-step approach to ensure high purity while maintaining structural integrity:
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Initial capture: Immobilized metal affinity chromatography (IMAC) using Ni-NTA or similar resin
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Intermediate purification: Ion exchange chromatography
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Polishing step: Size exclusion chromatography
The following protocol has been demonstrated to yield high-purity protein:
| Purification Step | Conditions | Purpose |
|---|---|---|
| Cell lysis | Sonication or pressure homogenization in buffer containing 50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10 mM imidazole, 1 mM DTT | Release protein from cells while maintaining reducing environment |
| IMAC | Binding: 50 mM Tris-HCl pH 8.0, 300 mM NaCl, 10 mM imidazole; Washing: increase to 20-40 mM imidazole; Elution: 250-300 mM imidazole | Remove bulk contaminants |
| Buffer exchange | 20 mM Tris-HCl pH 7.5, 50 mM NaCl | Prepare for ion exchange |
| Ion exchange | Linear gradient of 50-500 mM NaCl | Remove remaining contaminants |
| Size exclusion | 20 mM Tris-HCl pH 7.5, 150 mM NaCl | Final polishing and buffer exchange |
After purification, the protein should be assessed for purity using SDS-PAGE, with expected purity greater than 90% .
What storage and reconstitution protocols optimize petA stability?
Optimal storage conditions for purified petA protein include:
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Short-term storage (up to one week): 4°C in appropriate buffer
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Long-term storage: -20°C or -80°C as aliquots to avoid repeated freeze-thaw cycles
For reconstitution and storage of lyophilized protein:
| Step | Protocol | Rationale |
|---|---|---|
| Initial handling | Brief centrifugation to bring contents to bottom of vial | Ensures complete recovery |
| Reconstitution | Add deionized sterile water to 0.1-1.0 mg/mL | Controls protein concentration |
| Stabilization | Add glycerol to 5-50% final concentration (50% recommended) | Prevents ice crystal formation |
| Aliquoting | Divide into single-use volumes | Avoids repeated freeze-thaw cycles |
The recommended storage buffer is Tris/PBS-based with 6% trehalose at pH 8.0 . Trehalose acts as a cryoprotectant and stabilizer for the protein structure. Researchers should avoid repeated freeze-thaw cycles as this can lead to protein denaturation and loss of the iron-sulfur cluster.
How can electron transport activity of petA be measured in vitro?
Measuring the electron transport activity of petA requires assessing its ability to transfer electrons within the cytochrome bc1 complex. Several methodologies can be employed:
| Assay Type | Methodology | Data Interpretation |
|---|---|---|
| Spectrophotometric assay | Monitor reduction of cytochrome c at 550 nm | Rate of absorbance increase indicates electron transfer rate |
| Oxygen consumption | Clark-type electrode measuring oxygen reduction | Rate of oxygen consumption correlates with electron transport activity |
| Artificial electron acceptor reduction | Reduction of 2,6-dichlorophenolindophenol (DCPIP) | Color change from blue to colorless indicates electron transfer |
A standard spectrophotometric protocol involves:
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Prepare reaction mixture containing buffer (50 mM potassium phosphate, pH 7.5), purified petA protein, ubiquinol (substrate), and cytochrome c
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Initiate reaction by adding ubiquinol
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Monitor absorbance at 550 nm for 5 minutes
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Calculate initial velocity from the linear portion of the progress curve
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Determine specific activity as nmol cytochrome c reduced per minute per mg protein
Controls should include reactions without petA protein and with heat-inactivated petA to establish baseline and non-specific reduction rates.
What methods can accurately analyze iron-sulfur cluster integrity in recombinant petA?
The integrity of the iron-sulfur cluster is critical for petA function and can be assessed using multiple complementary techniques:
| Technique | Measurement | Information Obtained |
|---|---|---|
| UV-visible spectroscopy | Absorption spectrum 300-700 nm | Characteristic peaks at ~330, ~430, and ~550 nm |
| Electron paramagnetic resonance (EPR) | Spin state of Fe-S cluster | Oxidation state and electronic environment |
| Circular dichroism (CD) | Ellipticity in visible region | Secondary structure and cluster environment |
| Iron and sulfide quantification | Colorimetric assays | Stoichiometry of Fe and S in purified protein |
A comprehensive analysis should include multiple methods to confirm cluster integrity. For example, the characteristic absorption spectrum of the Rieske [2Fe-2S] cluster shows distinct peaks that change upon reduction. Additionally, quantitative analysis of iron and sulfide content should match the expected 2:2 ratio for a [2Fe-2S] cluster.
How can petA be utilized in drug development targeting Rickettsia infections?
The petA protein represents a potential drug target due to its essential role in Rickettsia energy metabolism. Strategic approaches for exploiting petA in drug development include:
| Approach | Methodology | Expected Outcomes |
|---|---|---|
| Structure-based drug design | In silico docking of compounds to crystal structure or homology model | Identification of high-affinity binding compounds |
| High-throughput screening | Screening compound libraries against purified petA | Discovery of inhibitors with specificity for bacterial protein |
| Fragment-based drug discovery | Building compounds from smaller fragments that bind to different sites | Development of high-specificity inhibitors |
| Natural product screening | Testing natural products with known antibiotic properties | Identification of novel scaffold structures |
Researchers should note that effective inhibitors would likely target the unique aspects of the bacterial Rieske protein that differ from the human homolog. The success rate of traditional animal models in predicting human responses to drugs is notably low, with 95% failure rate in clinical trials for drugs that appeared safe and effective in animal tests . This underscores the importance of employing human-relevant research methods when advancing from in vitro studies to clinical applications.
What data contradiction analysis methods are most effective when studying petA function?
When analyzing contradictory data regarding petA function, researchers should employ systematic approaches to identify the source of discrepancies:
When contradictions arise, they should be documented using formal contradiction annotation systems similar to those used in linguistic analysis . For example, applying a 3-way decision framework (YES/NO/UNKNOWN) to experimental outcomes can help categorize apparent contradictions and identify whether they represent true biological differences or methodological artifacts.
What non-animal methods can effectively study petA function in host-pathogen interactions?
In line with the principles of the Research Modernization Deal advocated by scientific organizations , researchers can employ several human-relevant models to study petA function:
| Non-animal Method | Application | Advantages |
|---|---|---|
| Human cell culture models | Primary human endothelial cells infected with Rickettsia | Directly relevant to human infection process |
| Microfluidic "organs-on-chips" | Vascular endothelium chips with flowing medium | Replicates physiological conditions of infection |
| Ex vivo human tissue models | Human skin explants | Maintains tissue architecture and cellular interactions |
| Computational modeling | In silico prediction of drug-target interactions | Rapid screening without biological materials |
These methods align with the recognition that animal models often fail to translate to human outcomes, with failure rates exceeding 95% in multiple disease areas including infectious diseases . Implementation of these human-relevant approaches not only addresses ethical concerns but also potentially increases translational success by focusing on human biology from the outset.
How can researchers integrate computational approaches to enhance petA research?
Computational methods can significantly advance petA research while reducing reliance on traditional experimental approaches:
| Computational Approach | Application | Research Benefit |
|---|---|---|
| Homology modeling | Prediction of protein structure | Guides experimental design without crystal structure |
| Molecular dynamics simulations | Analysis of protein dynamics and interactions | Insights into functional mechanisms |
| Sequence analysis and conservation mapping | Identification of critical residues | Prioritization of targets for mutagenesis |
| Virtual screening | In silico identification of potential inhibitors | Efficient use of resources in drug discovery |
These techniques represent an important component of the research modernization strategy that aims to replace methods with poor translational outcomes with more effective, human-relevant approaches . By incorporating these computational methods, researchers can design more targeted experiments, potentially reducing research costs and accelerating discovery while adhering to ethical research principles.
What are the most promising future research directions for petA studies?
Based on current understanding and technological capabilities, several research directions show particular promise:
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Integration of structural biology with functional studies to clarify the precise mechanism of electron transfer
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Development of petA-specific inhibitors as potential therapeutic agents against Rickettsia infections
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Application of systems biology approaches to understand petA's role in the context of complete bacterial metabolism
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Examination of host-pathogen interactions mediated by respiratory chain components including petA
These directions align with the broader shift in biomedical research toward human-relevant methodologies that offer greater translational value than traditional approaches. As highlighted by research modernization initiatives, focusing on human-based methods may significantly improve the success rate of therapeutic development compared to the current paradigm where 90% of basic research, much involving animal models, fails to lead to human treatments .
Human-relevant research methods combined with advanced computational approaches offer the most promising path forward for understanding petA function and developing targeted interventions against Rickettsia infections.
