Recombinant Corynebacterium urealyticum ATP synthase subunit delta (atpH)
Description
Molecular Characterization of ATP Synthase Subunit Delta (atpH)
The atpH gene encodes the delta subunit of the F1F0-ATP synthase, a membrane-bound enzyme responsible for ATP production via oxidative phosphorylation. In C. urealyticum, the atpH gene is part of a conserved operon structure:
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Gene locus: Located between atpA (alpha subunit) and atpG (gamma subunit) in the ATP synthase operon .
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Function: Stabilizes the F1 sector and facilitates coupling between the F1 and F0 complexes during proton translocation .
Table 1: Genomic Organization of the ATP Synthase Operon in C. urealyticum
Antimicrobial Resistance Context
C. urealyticum is intrinsically multidrug-resistant, complicating treatment. Key resistance mechanisms include:
The ATP synthase complex, including atpH, is not directly implicated in resistance but is a potential target for novel antimicrobials due to its essential role in energy production .
Genomic and Proteomic Studies
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Chromosomal analysis: The C. urealyticum DSM 7109 genome (2.8 Mb) contains three rrn operons and 51 tRNA genes, reflecting adaptability to diverse niches .
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Surface adherence: Proteins like SurA and SurB facilitate biofilm formation on catheters, a key virulence factor .
Table 2: Key Genomic Features of C. urealyticum DSM 7109
| Feature | Detail |
|---|---|
| Genome size | ~2.8 Mb |
| tRNA genes | 51 |
| rrn operons | 3 |
| Putative virulence factors | surA, surB, urease (ureABC) |
Research Gaps and Future Directions
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Recombinant protein studies: No direct biochemical data on recombinant atpH exist, though homology modeling with C. jeikeium structures could predict its role in ATP synthase assembly .
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Therapeutic targeting: Inhibiting ATP synthase could disrupt biofilm formation or urea metabolism, but in vitro assays (e.g., MTT, adhesion studies) are needed to validate efficacy .
Product Specs
Target Background
KEGG: cur:cu0713
STRING: 504474.cur_0713
Q&A
What is Corynebacterium urealyticum and why is its ATP synthase significant?
Corynebacterium urealyticum is a Gram-positive, slow-growing, lipophilic, multi-drug resistant, urease-positive microorganism with diphtheroid morphology. It was originally characterized based on its biochemical properties, including the ability to hydrolyze urea, and was formerly known as coryneform CDC group D2. This opportunistic nosocomial pathogen has been implicated in various infections including cystitis, pyelonephritis, and bacteremia, particularly in immunocompromised patients .
ATP synthase in C. urealyticum represents a critical component of bacterial energy metabolism. The delta subunit (encoded by atpH, sometimes referred to as atpD in some literature) plays an essential structural role in the ATP synthase complex. Understanding this protein offers insights into bacterial bioenergetics and potential targets for antimicrobial development, especially important given the multidrug resistance profile of this organism .
What techniques are used to express and purify recombinant C. urealyticum ATP synthase subunit delta?
The expression and purification of recombinant C. urealyticum ATP synthase subunit delta requires specialized techniques to ensure proper folding and maintain functionality. The following methodological approach is recommended:
Expression systems:
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E. coli BL21(DE3) or Rosetta strains with codon optimization for high GC content genomes
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Temperature-controlled expression (typically 18-22°C) to minimize inclusion body formation
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IPTG induction at low concentrations (0.1-0.5 mM) to prevent toxicity
Purification strategy:
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Cell lysis using mild detergents to preserve protein structure
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Immobilized metal affinity chromatography (IMAC) with His-tagged constructs
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Size exclusion chromatography for final purification and buffer exchange
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Optional ion exchange chromatography for removal of nucleic acid contaminants
When working with membrane-associated proteins like components of ATP synthase, addition of stabilizing agents such as glycerol (10%) and reducing agents (1-5 mM DTT or TCEP) helps maintain protein integrity throughout the purification process.
How does the genomic organization of ATP synthase genes in C. urealyticum compare to other species?
The C. urealyticum genome exhibits several distinctive features that may impact ATP synthase gene organization. The C. urealyticum DSM7109 chromosome is smaller than that of other pathogenic corynebacteria by approximately 100 kb, suggesting gene reduction during evolution .
A notable genomic difference is the arrangement of ribosomal RNA operons (rrn). C. urealyticum has three rrn operons on the leading strands, with one on the right and two on the left replichore. This differs from the closely related C. jeikeium, which contains all three rrn operons on the right replichore, indicating significant structural rearrangements in the C. urealyticum chromosome .
While specific information about ATP synthase gene organization in C. urealyticum is limited, genomic comparison revealed that 78.5% of C. urealyticum DSM7109 proteins are orthologous with proteins from the C. jeikeium K411 genome, indicating a close phylogenetic relationship between these lipid-requiring species . This suggests potential conservation of ATP synthase gene organization, though species-specific variations may exist.
How does the delta subunit contribute to ATP synthase assembly and stability?
The delta subunit serves critical functions in ATP synthase assembly and stability:
Structural stabilization:
The delta subunit forms a peripheral stalk with subunits b and b' that acts as a stator to prevent unproductive rotation of the F₁ portion with the F₀ portion during catalysis. This stabilization is essential for efficient energy conversion .
Complex assembly regulation:
As demonstrated in plant systems, the abundance of the delta subunit (AtpD) directly correlates with electron transport rates. Plants with reduced AtpD show decreased linear electron flow and increased non-photochemical quenching, indicating the subunit's importance for optimal complex function .
Limiting component role:
Research in plant systems has demonstrated that overexpression of just the delta subunit can increase the abundance and activity of the entire ATP synthase complex. This suggests the delta subunit may be a limiting factor in complex assembly, potentially applicable to bacterial systems like C. urealyticum .
Signaling integration:
Nuclear-encoded subunits of energy-generating complexes (like the delta subunit) are often involved in signaling pathways that integrate energy production with cellular metabolism. This regulatory role may be particularly important in bacteria adapting to changing environments .
What structural domains in the ATP synthase delta subunit are critical for function?
While specific structural information for C. urealyticum ATP synthase delta subunit is limited, general structural domains in bacterial delta subunits include:
N-terminal domain:
C-terminal domain:
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Typically more flexible in structure
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Interacts with the peripheral stalk components (b and b' subunits)
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Critical for connecting the F₁ and F₀ portions
Interface regions:
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Contains specific residues for protein-protein interactions
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Includes conserved motifs for recognition of partner proteins
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Crucial for proper assembly and function
These structural elements ensure the delta subunit properly positions and stabilizes the ATP synthase complex during the conformational changes of rotary catalysis. Mutations in these regions could significantly impact energy conversion efficiency and bacterial viability.
How can site-directed mutagenesis of C. urealyticum ATP synthase delta subunit inform understanding of energy coupling?
Site-directed mutagenesis offers powerful insights into energy coupling mechanisms in ATP synthase. The following experimental approaches are particularly valuable:
Interface residue analysis:
Creating mutations at the interface between the delta subunit and other components allows identification of critical residues for complex stability. By systematically altering these residues and measuring effects on ATP synthesis, researchers can map the structural requirements for efficient energy coupling.
Comparative mutations:
Introducing mutations that convert residues unique to C. urealyticum to those found in homologous proteins from other species can reveal species-specific adaptations. This approach helps identify residues that may contribute to C. urealyticum's adaptation to its ecological niche as a skin and urinary tract colonizer .
Flexibility modulation:
ATP synthase function requires both stability and controlled flexibility. Mutations that alter the rigidity of specific regions of the delta subunit can help determine how mechanical properties influence energy coupling efficiency.
Methodological implementation:
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Generate recombinant delta subunit variants with targeted mutations
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Reconstitute ATP synthase complexes with mutant subunits
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Measure ATP synthesis rates in proteoliposome systems
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Assess complex stability through biochemical and biophysical techniques
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Correlate structural changes with functional outcomes
This approach has successfully identified critical residues in ATP synthase from other organisms and can be applied to understand the unique features of C. urealyticum energy metabolism.
What potential does the C. urealyticum ATP synthase delta subunit offer for antimicrobial development?
The C. urealyticum ATP synthase delta subunit represents a promising target for antimicrobial development for several reasons:
Essential function:
ATP synthase is crucial for bacterial energy production, making it a vital target. Disrupting the delta subunit could impair ATP synthesis and thereby bacterial viability, especially important as C. urealyticum is reported as multi-drug resistant .
Structural specificity:
The delta subunit's unique structural features could provide selectivity for targeted inhibitors. The interface between the delta subunit and other components represents a potential binding site for small molecules that could disrupt complex assembly or function.
Colonization disruption:
C. urealyticum is known to colonize human skin and urinary tract, especially in patients receiving broad-spectrum antibiotics . Targeting ATP synthase could potentially disrupt this colonization by interfering with the energy requirements for adherence mechanisms.
Experimental approaches:
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Structure-based design of small molecules targeting delta subunit interfaces
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High-throughput screening of compound libraries against purified protein
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Evaluation of lead compounds in bacterial culture systems
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Assessment of specificity by comparing effects on human ATP synthase
The development of ATP synthase inhibitors could represent a novel class of antibiotics with distinct mechanisms of action, potentially valuable against resistant strains like C. urealyticum.
What approaches can characterize interactions between the delta subunit and other ATP synthase components?
Multiple complementary approaches can elucidate interactions between the ATP synthase delta subunit and other components:
Biochemical techniques:
| Technique | Application | Advantages | Limitations |
|---|---|---|---|
| Co-immunoprecipitation | Identify interacting partners | Works with native complexes | Requires specific antibodies |
| Crosslinking | Map proximity of subunits | Captures transient interactions | May introduce artifacts |
| Surface plasmon resonance | Measure binding kinetics | Provides quantitative data | Requires purified components |
| Isothermal titration calorimetry | Determine thermodynamic parameters | Direct measurement of binding | Protein-consuming |
Structural approaches:
| Technique | Application | Resolution | Sample requirements |
|---|---|---|---|
| X-ray crystallography | High-resolution structure | Atomic (1-3Å) | Diffracting crystals |
| Cryo-electron microscopy | Whole complex visualization | Near-atomic (3-4Å) | Purified complex |
| NMR spectroscopy | Dynamic structural information | Atomic for domains | Size-limited (<30 kDa ideal) |
| Hydrogen-deuterium exchange MS | Identify interaction surfaces | Peptide-level | Purified proteins |
Genetic methods:
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Bacterial two-hybrid systems to screen for interactions in vivo
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Suppressor mutation analysis to identify compensatory mutations
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Conditional expression systems to control subunit abundance
A comprehensive understanding requires integration of data from multiple approaches, moving from identification of interactions to detailed characterization of binding interfaces and functional significance.
How can proteomics approaches advance understanding of C. urealyticum ATP synthase modifications?
Proteomics offers powerful tools for investigating post-translational modifications (PTMs) and processing of ATP synthase components:
Mass spectrometry-based approaches:
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Bottom-up proteomics with enrichment strategies for specific PTMs
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Top-down proteomics for intact protein analysis to preserve modification patterns
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Targeted MS approaches using selected reaction monitoring for quantification
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Crosslinking mass spectrometry to map structural relationships
PTM-specific methods:
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Phosphoproteomics using titanium dioxide or IMAC enrichment
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Redox proteomics to identify oxidative modifications
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Glycoproteomics if glycosylation is suspected
Biological context analysis:
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Temporal profiling during different growth phases
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Comparison between drug-resistant and sensitive strains
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Analysis under different stress conditions
Data interpretation framework:
| PTM type | Potential function | Detection approach | Validation method |
|---|---|---|---|
| Phosphorylation | Activity regulation | Phospho-enrichment MS | Site-directed mutagenesis |
| Acetylation | Metabolic regulation | Antibody enrichment, MS | Deacetylase inhibitors |
| S-glutathionylation | Redox protection | Thiol-trapping, MS | Reducing agent sensitivity |
| Proteolytic processing | Assembly control | N-terminal labeling | Protease inhibitor studies |
These approaches can reveal how C. urealyticum regulates ATP synthase activity in response to environmental conditions, potentially illuminating adaption mechanisms relevant to its pathogenicity and antibiotic resistance.
What are key unresolved questions about C. urealyticum ATP synthase function?
Several important questions remain unanswered regarding C. urealyticum ATP synthase:
Evolutionary adaptations: How has C. urealyticum ATP synthase adapted to the organism's ecological niche as a skin and urinary tract colonizer? The genome of C. urealyticum shows evidence of reduction compared to other corynebacteria , raising questions about potential streamlining of energy production systems.
Regulatory mechanisms: What mechanisms regulate ATP synthase activity in response to environmental conditions encountered during colonization and infection? Understanding these regulatory pathways could reveal targets for disrupting adaptation to host environments.
Structural uniqueness: Are there structural features unique to C. urealyticum ATP synthase that could be exploited for specific targeting? Comparative analysis with ATP synthases from other species could identify distinguishing characteristics.
Role in pathogenesis: How does ATP synthase function contribute to C. urealyticum pathogenicity? The organism's ability to cause infections like encrusted cystitis may be linked to its energy metabolism capabilities under specific host conditions.
Resistance connections: Is there a relationship between ATP synthase function and the multidrug resistance phenotype observed in C. urealyticum? Energy-dependent efflux pumps require ATP, suggesting potential indirect connections.
Addressing these questions will require interdisciplinary approaches combining structural biology, biochemistry, genetics, and clinical microbiology.
What technical challenges exist in studying C. urealyticum ATP synthase subunits?
Researchers face several technical challenges when studying C. urealyticum ATP synthase:
Cultivation difficulties:
C. urealyticum is slow-growing and lipophilic, requiring extended incubation periods (48 hours at 35-37°C, preferably in 10% CO₂) for isolation . This complicates obtaining sufficient biomass for biochemical studies.
Expression obstacles:
Heterologous expression of C. urealyticum proteins presents challenges due to:
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High G+C content affecting codon usage in common expression hosts
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Potential toxicity when expressing energy-related proteins
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Requirements for correct assembly with partner proteins
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Lipophilic nature potentially affecting folding
Structural analysis limitations:
ATP synthase is a complex multi-subunit assembly with both membrane and soluble components, making structural studies challenging. Individual subunits like delta may not adopt native conformations when isolated from the complex.
Functional reconstitution:
Assessing ATP synthase function requires reconstitution of the complete complex in a membrane environment, a technically demanding process requiring multiple purified components and careful control of membrane composition.
Genetic manipulation constraints:
Limited genetic tools are available for direct manipulation of C. urealyticum compared to model organisms, complicating in vivo studies of ATP synthase function and regulation.
Researchers can address these challenges through strategies like codon optimization, fusion partners to enhance solubility, and development of cell-free expression systems tailored to high-GC content organisms.
