Recombinant Desulforudis audaxviator UPF0059 membrane protein Daud_2150 (Daud_2150)

What is Candidatus Desulforudis audaxviator and why is it significant for research?

Candidatus Desulforudis audaxviator is a bacterium belonging to the Firmicutes phylum, specifically within the Clostridia class and Thermoanaerobacterales order . It gained scientific prominence when discovered in a South African gold mine's fracture water at 2.8 kilometers depth, where it formed a remarkable single-species ecosystem . This organism is significant because it exemplifies extreme adaptation to deep subsurface conditions, possessing unique metabolic capabilities including motility, sporulation, sulfate reduction, and chemoautotrophy with the ability to fix both nitrogen and carbon . Its genome contains machinery shared with archaea, suggesting evolutionary adaptations that enable survival in isolated, nutrient-limited environments . Recent research has challenged earlier assumptions about its extremely slow growth rate by isolating a cultivable strain (BYF) from a 2-km deep aquifer in Western Siberia that demonstrates a doubling time of approximately 28.5 hours under laboratory conditions .

What is the structure and function of the UPF0059 membrane protein Daud_2150?

The UPF0059 membrane protein Daud_2150 is a 180 amino acid transmembrane protein from Desulforudis audaxviator with UniProt accession number B1I6K8 . Based on its amino acid sequence (MTAGTVLLLAGALGTDAFSLCLGLGLNGFRRRMAWMLVGLIVALhvvlpvagwyageftgrlvgrwaaylgaailfylgvkmvreslaegrtatgkleragflgltvlagsvsmdalsvgftlgtagaallltagviglvaglmsaaafvlahrvedwvgrraellgglvligvglrllf), it contains multiple hydrophobic regions consistent with transmembrane domains . While the precise function remains under investigation, structural analysis indicates it belongs to the UPF0059 family of membrane proteins that are conserved across various bacterial species, suggesting fundamental cellular importance. The protein likely contributes to membrane integrity and possibly participates in membrane transport processes critical for D. audaxviator's survival in extreme environments, potentially including roles in energy metabolism or nutrient acquisition systems.

How can researchers express and purify recombinant Daud_2150 protein?

The recombinant Daud_2150 protein can be efficiently expressed in E. coli expression systems using a His-tag fusion construct for simplified purification . The recommended methodology involves:

• Cloning the full-length gene (encoding amino acids 1-180) into an expression vector with an N-terminal His-tag.

• Transforming the construct into an appropriate E. coli strain optimized for membrane protein expression.

• Inducing protein expression under controlled conditions to prevent formation of inclusion bodies.

• Lysing cells and solubilizing membrane fractions using appropriate detergents.

• Purifying using immobilized metal affinity chromatography (IMAC) with Ni-NTA resin.

• Performing size exclusion chromatography for further purification if needed.

• Storing the purified protein in a Tris-based buffer containing 50% glycerol at -20°C for short-term or -80°C for extended storage .

This approach yields functional protein suitable for biochemical, structural, and functional studies. For optimal results, researchers should avoid repeated freeze-thaw cycles and maintain working aliquots at 4°C for no more than one week .

How does Daud_2150 integrate into the broader metabolic framework of D. audaxviator?

The Daud_2150 membrane protein likely plays an integral role within D. audaxviator's highly specialized metabolic network that enables its survival in extreme environments. Genomic analysis reveals that D. audaxviator possesses a complete dissimilatory sulfate reduction (DSR) pathway organized in specific operons (labeled SR1-SR11) , alongside high-potential electron transport via hydrogenases that utilize H₂ as an electron donor . The Daud_2150 protein may function within this metabolic framework in several possible ways:

• Membrane integrity maintenance in extreme conditions

• Facilitation of ion or nutrient transport across the membrane

• Potential involvement in energy conservation mechanisms

• Possible role in stress response or environmental sensing

Based on comparative genomic analyses across sulfate-reducing bacteria, the protein's membrane localization suggests it might contribute to the unique adaptation of D. audaxviator to its niche environment, potentially interfacing with cellular systems for carbon fixation via the acetyl-CoA synthesis (Wood-Ljungdahl) pathway . Future research combining proteomics with metabolic flux analysis would help establish the protein's precise role in the organism's sophisticated metabolic machinery.

What experimental approaches are recommended for investigating Daud_2150 function in membrane dynamics?

To elucidate the function of Daud_2150 in membrane dynamics, researchers should employ a multi-faceted experimental approach:

Recommended Experimental Strategy:

This integrated approach should be complemented with computational modeling to predict protein-membrane interactions. Researchers should pay particular attention to the hydrophobic regions in the amino acid sequence that likely form transmembrane domains . The complex intracellular organization of D. audaxviator, which includes internal membranes and electron-dense structures containing phosphorus, iron, and calcium , suggests Daud_2150 may participate in specialized membrane compartmentalization relevant to the organism's unique physiology.

How can researchers address contradictions in experimental data regarding Daud_2150 functionality?

When addressing contradictions in experimental data concerning Daud_2150 functionality, researchers should implement a systematic approach to contradiction resolution based on context analysis principles:

• Contradiction categorization: Classify contradictions according to the framework proposed by Alamri, which distinguishes between different relation types (excitatory, inhibitory, or other) . For example, contradictory findings about Daud_2150 might fall into patterns such as "Protein A activates Daud_2150" versus "Protein A inhibits Daud_2150."

• Context extraction: For each contradictory claim, document the experimental conditions in detail, including:

  • Expression system used

  • Purification methodology

  • Buffer composition and pH

  • Temperature and pressure conditions

  • Presence of cofactors or metal ions (particularly iron, which is required for D. audaxviator growth )

  • Membrane environment (detergent type, lipid composition)

• Normalization of terminology: Establish a standardized terminology for Daud_2150 research to address the issue noted by Alamri regarding acronyms and normalization problems in contradiction detection .

• Statistical validation: Employ statistical methods to determine whether contradictions represent genuine biological phenomena or experimental artifacts.

• Integration of multiple data types: Combine functional assays with structural and computational data to build a comprehensive model that can accommodate apparently contradictory observations.

This methodology can help resolve contradictions by identifying conditional dependencies in Daud_2150 functionality, which may be particularly important given that D. audaxviator exhibits different metabolic capabilities depending on environmental conditions, such as using either hydrogen or various organic electron donors for sulfate respiration .

What are the implications of D. audaxviator's extreme environment adaptation for interpreting Daud_2150 experimental results?

The extreme adaptation of Desulforudis audaxviator to deep subsurface environments has profound implications for interpreting experimental results related to Daud_2150:

• Pressure considerations: Native function occurs at high hydrostatic pressure (at depths of 2-2.8 km) , which may significantly alter protein conformation and activity compared to standard laboratory conditions. Researchers should consider using high-pressure bioreactors for more physiologically relevant assays.

• Temperature effects: D. audaxviator is described as a thermophile , suggesting Daud_2150's optimal functional temperature may be higher than standard laboratory conditions. Thermal stability and activity profiles should be established across a range of temperatures.

• Nutrient limitation adaptation: The protein evolved in an extremely nutrient-limited environment , potentially resulting in multifunctional properties that might not be apparent in nutrient-rich experimental systems.

• Redox conditions: The native reducing environment contains significant hydrogen from water radiolysis . Experimental conditions should maintain appropriate redox potential to preserve native protein functionality.

• Iron dependency: Growth of D. audaxviator requires elemental iron, with ferrous iron unable to substitute . This suggests potential iron-protein interactions that might be critical for Daud_2150 function but could be overlooked in standard experimental setups.

• Long-term stability: The organism was originally thought to divide extremely slowly (hundreds to thousands of years) , suggesting its proteins may have unusual stability properties that should be considered when designing experiments and interpreting results.

Researchers should design experiments that mimic these extreme conditions when possible, or at minimum acknowledge these limitations when interpreting results obtained under standard laboratory conditions.

What protocols are recommended for studying membrane insertion of Daud_2150?

To study membrane insertion of Daud_2150, researchers should employ a comprehensive protocol combining in vitro and in silico approaches:

In Vitro Membrane Insertion Protocol:

• Preparation of Daud_2150 in a membrane-compatible state:

  • Express the protein with the His-tag as described in available literature .

  • Purify in the presence of mild detergents that maintain native conformation.

  • Verify protein quality using circular dichroism to confirm secondary structure.

• Model membrane system preparation:

  • Prepare liposomes with lipid compositions mimicking D. audaxviator membranes.

  • Consider including specific lipids found in extremophiles that might facilitate protein function.

  • Label liposomes with fluorescent markers to track membrane integrity.

• Membrane insertion assay:

  • Incubate purified Daud_2150 with prepared liposomes.

  • Monitor insertion using protease protection assays (regions inserted into membranes become protected from protease digestion).

  • Use fluorescence resonance energy transfer (FRET) to track conformational changes during insertion.

  • Employ freeze-fracture electron microscopy to visualize inserted protein.

• Functional verification:

  • Assess liposome permeability changes upon protein insertion.

  • Measure potential ion flux across membranes using ion-selective electrodes.

  • Evaluate protein orientation using asymmetrically applied antibodies against specific domains.

• Environmental variable testing:

  • Repeat insertion experiments under varying conditions of:

    • Temperature (including thermophilic range)

    • pH

    • Pressure (using specialized high-pressure equipment)

    • Salt concentration

    • Presence of potential cofactors, especially iron compounds

This protocol should be complemented with computational approaches predicting transmembrane domains and insertion mechanisms based on the known amino acid sequence .

How can researchers effectively design experiments to study the role of Daud_2150 in D. audaxviator's stress response?

To effectively study Daud_2150's role in stress response, researchers should implement a systems biology approach integrating multiple experimental techniques:

Experimental Design Framework:

• Transcriptomic profiling:

  • Compare daud_2150 expression levels under various stress conditions (heat, oxidative stress, nutrient limitation, pressure changes).

  • Use RNA-seq to identify genes co-regulated with daud_2150, suggesting functional relationships.

  • Create a regulatory network map positioning Daud_2150 within stress response pathways.

• Protein interaction studies:

  • Perform pull-down assays using tagged Daud_2150 to identify interaction partners under different stress conditions.

  • Validate interactions using techniques such as bioluminescence resonance energy transfer (BRET) or split-GFP complementation.

  • Map the dynamic interactome of Daud_2150 during stress response progression.

• Heterologous expression systems:

  • Express Daud_2150 in stress-sensitive model organisms (E. coli mutants or yeast).

  • Assess whether Daud_2150 expression confers increased resistance to stressors typical of deep subsurface environments.

  • Create chimeric proteins with domains from related organisms to identify functional regions.

• Structural studies under stress conditions:

  • Analyze conformational changes in Daud_2150 under various stressors using hydrogen-deuterium exchange mass spectrometry.

  • Perform stability studies under extremes of temperature, pressure, and pH.

  • Identify post-translational modifications that might regulate protein function during stress.

• Comparative genomics approach:

  • Analyze homologs of Daud_2150 in related extremophiles.

  • Identify conserved domains that might indicate shared stress response functions.

  • Construct evolutionary models to understand adaptation of this protein family to extreme environments.

This experimental framework should explicitly account for D. audaxviator's unique adaptations, including its complex intracellular organization with gas vesicles, internal membranes, and electron-dense structures enriched in phosphorus, iron, and calcium .

What emerging technologies could advance our understanding of Daud_2150 function?

Several cutting-edge technologies hold promise for advancing our understanding of Daud_2150 function:

• Cryo-electron tomography: This technique could reveal the in situ organization of Daud_2150 within the complex intracellular structure of D. audaxviator, including its relationship to internal membranes and electron-dense structures . By visualizing the protein in its native cellular context, researchers could gain insights into its functional associations.

• Single-molecule force spectroscopy: This approach could measure the mechanical stability and unfolding characteristics of Daud_2150, providing insights into how the protein maintains structural integrity under extreme conditions.

• High-pressure structural biology techniques: Recently developed high-pressure NMR and crystallography methods could reveal structural changes in Daud_2150 under conditions mimicking its native deep subsurface environment.

• Microfluidic organ-on-a-chip systems: Adapted for microbial communities, these systems could allow researchers to recreate the unique environmental conditions of deep subsurface habitats and study Daud_2150 function in a more physiologically relevant context.

• CRISPR-based genome editing in extremophiles: As genetic manipulation tools for extremophiles advance, researchers might be able to directly modify daud_2150 in D. audaxviator or related organisms to study its function through precise genetic perturbations.

• In-cell NMR spectroscopy: This emerging technique could potentially provide atomic-level information about Daud_2150 structure and dynamics within living cells.

• AlphaFold and related AI methods: These artificial intelligence approaches could predict Daud_2150 structure with high accuracy, particularly as they improve in modeling membrane proteins, providing a foundation for function prediction.

These technologies, applied in combination, could overcome current limitations in studying proteins from extremophiles like D. audaxviator.

How might comparative analyses between Daud_2150 and homologous proteins inform evolutionary adaptation research?

Comparative analyses between Daud_2150 and its homologs can provide valuable insights into evolutionary adaptation mechanisms:

This comparative approach is particularly valuable given D. audaxviator's evolutionary adaptations that include machinery shared with archaea and its ability to thrive in isolated deep subsurface environments where it was once thought to divide extremely slowly .

What are the optimal storage and handling conditions for recombinant Daud_2150 protein preparations?

Based on available product information, the following storage and handling conditions are recommended for maintaining optimal activity of recombinant Daud_2150 protein:

Storage Conditions Table:

Handling Recommendations:

• Store the purified protein in appropriate volumes to avoid repeated freeze-thaw cycles, which can compromise protein integrity .

• For experimental procedures, thaw aliquots rapidly at room temperature or in a water bath, then maintain on ice until use.

• If the protein is to be used for functional studies, consider supplementing buffers with trace elements, particularly iron compounds, given the iron requirement observed in D. audaxviator .

• For structural studies, maintain reducing conditions to prevent oxidation of cysteine residues present in the amino acid sequence (MTAGTVLLLAGALGTDAFSLCLGLGLNGFRRRMAWMLVGLIVALH VVLPVAGWYAGEFTGRLVGRWAAYLGAAILFYLGVKMVRESLAEGRTATGKLERAGFLGLTVLAGSVSMDALSVGFTLGTAGAALLLTAGVIGLVAGLMSAAAFVLAHRVEDWVGRRAELLGGLVLIGVGLRLLF) .

• When designing experiments, account for the potential effect of pressure on protein conformation, given D. audaxviator's native high-pressure environment at 2-2.8 km depth .

These recommendations are based on standard practices for membrane proteins while considering the unique properties of D. audaxviator as an extremophile from deep subsurface environments.

How should researchers integrate Daud_2150 studies with broader investigations of extremophile adaptation mechanisms?

To effectively integrate Daud_2150 studies with broader extremophile research, investigators should adopt a multi-scale, collaborative approach:

• Contextual positioning within cellular systems:

  • Map Daud_2150 interactions with other cellular components, especially those involved in D. audaxviator's unique metabolic capabilities such as the dissimilatory sulfate reduction pathway .

  • Investigate potential roles in specialized cellular structures such as gas vesicles and internal membranes observed in D. audaxviator .

  • Examine relationships with electron-dense structures enriched in phosphorus, iron, and calcium that have been identified in D. audaxviator cells .

• Integration with multi-omics data:

  • Correlate Daud_2150 expression patterns with metabolomic profiles under varying conditions.

  • Use proteomics to identify post-translational modifications that might regulate Daud_2150 function in response to environmental stressors.

  • Apply systems biology approaches to position Daud_2150 within the broader adaptive network of D. audaxviator.

• Collaborative research framework:

  • Establish interdisciplinary collaborations between molecular biologists, structural biologists, geomicrobiologists, and evolutionary biologists.

  • Develop standardized protocols for comparing membrane proteins across extremophile species.

  • Create shared databases of extremophile protein function and adaptation mechanisms.

• Environmental context consideration:

  • Design experiments that explicitly account for D. audaxviator's native environmental conditions, including high pressure, nutrient limitation, and specific mineral composition.

  • Investigate how Daud_2150 function might relate to the organism's ability to form a single-species ecosystem in its natural habitat .

  • Consider the protein's potential role in D. audaxviator's surprising metabolic versatility, which enables it to use not only hydrogen but also various organic electron donors for sulfate respiration .

By adopting this integrated approach, researchers can position Daud_2150 studies within the broader context of extremophile adaptation, contributing to our understanding of life in extreme environments while potentially revealing novel molecular mechanisms with applications in biotechnology and astrobiology.