Recombinant Alkaliphilus oremlandii UPF0365 protein Clos_1242 (Clos_1242)

What is Alkaliphilus oremlandii UPF0365 protein Clos_1242?

Alkaliphilus oremlandii UPF0365 protein Clos_1242 is a 333-amino acid protein (10.5 kDa) expressed in the bacterium Alkaliphilus oremlandii strain OhILAs. This bacterium is a mesophilic, spore-forming, motile, gram-positive organism with specific capabilities related to arsenic metabolism. The UPF0365 protein belongs to a family of proteins with uncharacterized function, with the "UPF" designation indicating "Uncharacterized Protein Family" . The protein contains a multi-stranded β barrel structure with an intervening helix insert region, contributing to its structural stability and potential functional properties in arsenate metabolism .

How is Alkaliphilus oremlandii cultured in laboratory conditions?

Alkaliphilus oremlandii requires specific growth conditions due to its anaerobic nature and alkaline preferences:

• Growth Medium: The bacterium was originally enriched from Ohio River sediments using a basal medium supplemented with 20 mM lactate and 5 mM arsenate .

• pH Requirements: The optimal pH for growth is 8.4, reflecting its alkaliphilic nature .

• Anaerobic Conditions: As a strict anaerobe, cultures must be maintained in oxygen-free environments using anaerobic chambers or techniques like Hungate's method .

• Carbon Sources: A. oremlandii can ferment lactate via the acrylate pathway, as well as utilize fructose and glycerol as carbon sources .

• Electron Acceptors: For respiratory growth, arsenate and thiosulfate can serve as terminal electron acceptors .

A typical isolation protocol involves enrichment on basal medium, followed by passage on medium with increasing arsenic concentration (10-20 mM), tindalization (fractional sterilization), and serial dilution techniques .

What expression systems are optimal for recombinant UPF0365 protein?

While specific expression systems optimized for UPF0365 protein are not directly reported in the provided search results, general principles for recombinant protein expression can be applied:

• E. coli Expression System: The BL21(DE3) strain is commonly used for protein expression due to its efficiency and versatility . This system uses T7 RNA polymerase under the control of the lac promoter, which can be induced using IPTG.

• Temperature Optimization: Lower temperatures (15-25°C) during induction often improve the solubility of recombinant proteins by slowing down protein synthesis and allowing more time for proper folding .

• Media Selection: Rich media formulations improve yield but may affect protein solubility differently than minimal media. Testing both LB and super-rich media is recommended for optimization .

• Induction Time: Varying induction times (3-16 hours) significantly impacts protein yield and solubility, with longer times generally providing higher yields but potentially more insoluble protein .

An experimental design for optimization could follow this format:

What purification methods are recommended for UPF0365 protein?

For purification of recombinant UPF0365 protein, several approaches can be implemented:

• Affinity Chromatography: If the recombinant protein is expressed with a histidine tag, Ni-NTA or IMAC (Immobilized Metal Affinity Chromatography) would be the primary purification method .

• Buffer Optimization: The storage buffer should be Tris-based with 50% glycerol for stability, as recommended for this protein .

• Temperature Considerations: Storage at -20°C is recommended for short-term use, while -80°C is preferred for extended storage. Working aliquots can be maintained at 4°C for up to one week to minimize freeze-thaw cycles .

• Membrane Protein Considerations: Since UPF0365 likely contains transmembrane domains, solubilization with appropriate detergents may be necessary. Perfluorooctanoic acid (PFOA) has properties similar to sodium dodecyl sulfate (SDS) and can be effective for solubilizing membrane proteins prior to analysis .

How does the UPF0365 protein contribute to arsenic metabolism in A. oremlandii?

A. oremlandii possesses sophisticated arsenic metabolism capabilities, with several proteins playing key roles:

• Arsenate Respiratory Reduction: A. oremlandii can use arsenate as a terminal electron acceptor with various electron donors including acetate, pyruvate, formate, lactate, fumarate, glycerol, and fructose .

• Arsenate Reductase System: The bacterium has a constitutively expressed respiratory arsenate reductase, with the structural subunit encoded by the arrA gene. The entire arr operon and ars operon have been identified in the genome .

• Organoarsenical Transformation: A. oremlandii can transform the organoarsenical 3-nitro-4-hydroxy benzene arsonic acid (roxarsone), coupling the reduction of the nitro group to the oxidation of either lactate or fructose in a dissimilatory manner, generating ATP via a sodium-dependent ATP synthase .

What functional domains are predicted in the UPF0365 protein and how might they relate to its function?

Based on sequence analysis and structural predictions, the UPF0365 protein contains several key domains:

• N-terminal Transmembrane Domain: The hydrophobic N-terminal sequence (MPEVVFLLIVVAIAFIVLSIILSF) suggests membrane anchoring capability .

• β-barrel Structure: The core structure is predicted to be a multi-stranded β barrel with an intervening helix insert region .

• Potential Binding Sites: Sequence regions like "GIFTLVGMRFRRVQPNRIVG" and "VDALIAAQRAEIGLEFERAAAIDLAGR" contain patterns consistent with metal or substrate binding motifs.

These domains suggest the protein may function as:

• A membrane transporter for arsenate or organoarsenicals

• A sensor protein that detects arsenic compounds

• A component of a larger protein complex involved in arsenate respiration

Experimental approaches like domain swapping, deletion mutants, or site-directed mutagenesis would be needed to verify these functional predictions.

What experimental design would best elucidate UPF0365 protein expression under different arsenate conditions?

To study the expression patterns of UPF0365 protein under varying arsenate conditions, a comprehensive experimental design should include:

• Growth Conditions Matrix:

• Analytical Methods:

  • Quantitative proteomics using LC-MS/MS for both cytoplasmic and membrane fractions

  • RT-qPCR to measure gene expression levels

  • Western blotting with specific antibodies for protein quantification

  • Fluorescent reporter constructs to monitor expression in real-time

• Data Analysis:

  • Statistical comparison of protein abundance across conditions

  • Correlation analysis with other arsenate metabolism proteins

  • Temporal expression profiling at various growth phases

This design would reveal whether UPF0365 is constitutively expressed (like arrA) or induced under specific arsenate conditions, providing insight into its regulatory mechanisms and potential function .

What approaches are recommended for studying protein-protein interactions involving UPF0365?

Several complementary approaches can be employed to investigate protein-protein interactions of UPF0365:

• Co-immunoprecipitation (Co-IP): Using antibodies against UPF0365 to pull down interaction partners, followed by mass spectrometry identification. This method is particularly useful for stable, direct interactions.

• Bacterial Two-Hybrid System: Adapting bacterial two-hybrid systems to detect interactions in conditions that mimic the native anaerobic, alkaline environment of A. oremlandii.

• Cross-linking Mass Spectrometry: Chemical cross-linking followed by LC-MS/MS analysis can capture transient interactions and provide structural information about the complexes.

• Blue Native PAGE: For membrane proteins like UPF0365, blue native PAGE can preserve native protein complexes during electrophoresis.

• Proximity-based Labeling: BioID or APEX2 tagging of UPF0365 to identify proteins in close proximity under various growth conditions, including arsenate respiration.

When analyzing data from these experiments, researchers should specifically look for interactions with components of the arsenate reductase system and other proteins identified in the proteomic analysis of A. oremlandii grown under different arsenic conditions .

How can site-directed mutagenesis be applied to study the function of UPF0365 protein?

Site-directed mutagenesis provides a powerful approach to investigate structure-function relationships in UPF0365:

• Key Residues for Mutation:

  • Conserved residues in the predicted transmembrane domains

  • Potential metal-binding motifs (histidine, cysteine, or aspartate clusters)

  • Residues in the β-barrel structure that may form a pore or channel

  • The intervening helix region that may be involved in conformational changes

• Mutation Strategies:

  • Alanine scanning of conserved regions

  • Conservative substitutions to maintain structure but alter function

  • Charge reversal mutations to disrupt electrostatic interactions

  • Introduction of reporter groups or fluorescent tags at non-disruptive positions

• Functional Assays:

  • Growth rate measurements under arsenate conditions

  • Arsenate reduction activity assays

  • Membrane localization studies

  • Protein stability and folding analysis

• Expression System Considerations:

  • Complementation studies in A. oremlandii knockouts

  • Heterologous expression in E. coli with optimized conditions as described in section 1.4

  • In vitro translation systems for difficult mutations that affect protein folding

What expression optimization strategies are most effective for UPF0365 protein?

Optimizing expression of recombinant UPF0365 protein requires systematic exploration of multiple parameters:

• Codon Optimization: As UPF0365 comes from A. oremlandii, which has different codon usage than E. coli, codon optimization of the gene sequence can significantly improve expression levels .

• Design of Experiments (DoE) Approach: A factorial design testing multiple variables simultaneously is more efficient than one-at-a-time optimization:

• Solubility Enhancement:

  • Fusion partners: MBP, SUMO, or Thioredoxin tags

  • Co-expression with chaperones like GroEL/GroES

  • Addition of solubility enhancers to the media (sorbitol, glycine betaine)

• Analysis Methods:

  • SDS-PAGE for total protein expression

  • Western blotting for specific detection

  • Activity assays to confirm functional protein

The approach detailed in search result for testing multiple expression conditions simultaneously using the MaxQ 8000 refrigerated stackable shakers provides an excellent framework, allowing researchers to test all combinations of temperature, induction time, and media type in parallel .

How can researchers validate the activity of recombinant UPF0365 protein?

Validating the functional activity of recombinant UPF0365 protein presents challenges due to its uncharacterized nature, but several approaches can be employed:

• Structural Integrity Assessment:

  • Circular dichroism (CD) spectroscopy to confirm secondary structure elements

  • Thermal shift assays to assess protein stability

  • Size exclusion chromatography to verify oligomeric state

• Membrane Association Studies:

  • Liposome binding assays

  • Detergent solubility screening

  • Membrane fractionation of expression host cells

• Functional Assays Based on Predicted Roles:

  • If involved in arsenate transport: arsenate uptake or efflux assays

  • If part of a signaling system: ligand binding studies with arsenate compounds

  • If involved in arsenate reduction: coupling with known arsenate reductase components and measuring activity

• Comparative Proteomic Analysis:

  • Complementation studies in A. oremlandii knockouts

  • Protein-protein interaction screens with known arsenate metabolism components

  • Transcriptional responses to UPF0365 expression in heterologous hosts

What are the best approaches for studying UPF0365 protein in the context of arsenic biotransformation?

To understand UPF0365's role in arsenic biotransformation, integrated approaches combining multiple techniques are recommended:

• In vivo Studies:

  • Gene knockout or knockdown in A. oremlandii followed by phenotypic characterization

  • Expression of UPF0365 in heterologous hosts lacking arsenate metabolism capabilities

  • Real-time monitoring of arsenate reduction in wild-type vs. mutant strains

• Proteomic Analysis:

  • Shotgun proteomics using LC-MS/MS on both soluble cytoplasm and membrane fractions under different growth conditions

  • Comparison of protein abundance when grown with:

    • Sodium lactate (fermentative control)

    • Sodium lactate with roxarsone

    • Sodium lactate with 3-amino-4-hydroxybenzenearsonic acid

    • Sodium lactate with sodium arsenate

• Localization Studies:

  • Immunogold electron microscopy

  • Fluorescent protein fusions

  • Subcellular fractionation followed by Western blotting

• Systems Biology Approach:

  • Integration of transcriptomics, proteomics, and metabolomics data

  • Pathway modeling of arsenate metabolism including UPF0365

  • Correlation analysis between UPF0365 expression and arsenate reduction rates

How to address protein insolubility issues during UPF0365 expression?

Membrane proteins like UPF0365 often present solubility challenges during recombinant expression:

• Temperature Optimization:

  • Lower induction temperatures (15°C) generally increase solubility by slowing protein synthesis and allowing more time for proper folding

  • Extended induction times at lower temperatures can compensate for reduced expression rates

• Solubilization Strategies:

  • Detergent screening panel (mild detergents like DDM, LDAO, or Triton X-100)

  • Amphipols or nanodiscs for maintaining membrane protein structure

  • Perfluorooctanoic acid (PFOA) for analytical purposes

• Expression Construct Modifications:

  • Truncated constructs removing highly hydrophobic regions

  • Fusion to solubility-enhancing tags (MBP, SUMO)

  • Co-expression with binding partners if known

• Refolding Approaches:

  • Isolation of inclusion bodies followed by denaturation and controlled refolding

  • On-column refolding during purification

  • Stepwise dialysis with decreasing denaturant concentrations

What strategies can overcome low protein yield?

Several approaches can address low yield issues when working with UPF0365 protein:

• Expression System Optimization:

  • Testing different E. coli strains (C41/C43 for membrane proteins, Rosetta for rare codons)

  • Exploring alternative expression hosts (Bacillus species for gram-positive proteins)

  • Optimizing media composition (super rich media often increases yield)

• Gene and Vector Optimization:

  • Codon optimization for the expression host

  • Optimizing promoter strength and ribosome binding sites

  • Plasmid copy number considerations

• Induction Parameter Refinement:

  • Auto-induction media to eliminate manual IPTG addition

  • Testing various IPTG concentrations (0.1-1.0 mM)

  • Optimizing cell density at induction (OD600 of 0.6-0.8)

• Scale-up Considerations:

  • Maintaining adequate aeration in larger cultures

  • Temperature uniformity in larger vessels

  • Fed-batch approaches to maintain nutrient availability

How to verify protein function after purification?

Confirming that purified UPF0365 protein retains its native function requires multiple validation approaches:

• Activity Assays Based on Predicted Function:

  • If a transporter: reconstitution in liposomes and transport assays

  • If involved in arsenate metabolism: coupling with known components of the arsenate reduction pathway

  • If a structural protein: membrane association and oligomerization studies

• Structural Integrity Verification:

  • Circular dichroism to confirm secondary structure content

  • Thermal shift assays to measure stability and potential ligand binding

  • Limited proteolysis to assess proper folding

• Interaction Studies:

  • Pull-down assays with potential binding partners identified from proteomic studies

  • Surface plasmon resonance or microscale thermophoresis for binding kinetics

  • Native PAGE or size exclusion chromatography to detect complex formation

• Functional Complementation:

  • Expression in UPF0365 knockout strains to restore arsenate metabolism

  • Heterologous expression systems coupled with arsenate sensitivity/resistance tests

  • In vitro reconstitution of arsenate metabolism with purified components