Recombinant Psychromonas ingrahamii UPF0316 protein Ping_1367 (Ping_1367)

What is Psychromonas ingrahamii and what makes it unique among psychrophilic bacteria?

Psychromonas ingrahamii is an extreme psychrophilic bacterium isolated from sea ice cores collected at Point Barrow, Alaska. What distinguishes P. ingrahamii from other psychrophiles is its remarkable ability to grow exponentially at temperatures as low as -12°C, making it one of the most cold-adapted organisms known to science . Morphologically, P. ingrahamii cells are notably large (6-14 μm in length) and rod-shaped, containing gas vacuoles of two distinct morphologies that likely aid in adaptation to their environment .

The organism demonstrates optimal growth at NaCl concentrations between 1-10% and temperatures ranging from -12°C to 10°C, with a DNA G+C content of 40 mol% . Phylogenetic analysis based on 16S rRNA gene sequences places P. ingrahamii in close relation to Psychromonas antarctica (96.8% sequence similarity), though DNA-DNA hybridization experiments show only 37% relatedness, confirming its distinct species status . The combination of these features makes P. ingrahamii an exceptional model organism for studying biological mechanisms of extreme cold adaptation.

How does P. ingrahamii's protein composition differ from mesophilic bacteria?

Genomic and proteomic analyses of P. ingrahamii reveal several distinctive features that may contribute to its extreme psychrophilic nature:

The protein composition analysis suggests P. ingrahamii has evolved specific adaptations at the protein level that likely contribute to its ability to function at extremely low temperatures . These features provide important research targets for understanding cold adaptation mechanisms.

What are the recommended storage conditions for recombinant Ping_1367 protein?

Optimal storage of recombinant Ping_1367 protein should follow these guidelines based on similar recombinant proteins from psychrophilic organisms:

For short-term storage (up to one week), maintain aliquots at 4°C in a Tris-based buffer supplemented with 50% glycerol . For extended storage, keep the protein at -20°C or preferably at -80°C to minimize degradation . It is advisable to avoid repeated freeze-thaw cycles as this can lead to denaturation and loss of structural integrity .

When preparing the storage buffer, optimization for this specific protein is recommended, considering factors such as pH stability range, salt requirements, and potential need for reducing agents. Given the psychrophilic origin of the protein, it may exhibit greater stability at lower temperatures compared to mesophilic proteins, but empirical testing is necessary to confirm optimal conditions for each preparation.

How should researchers design experiments to study Ping_1367's potential role in cold adaptation?

When designing experiments to investigate Ping_1367's potential role in cold adaptation, researchers should employ a comprehensive approach including:

• Comparative expression analysis: Measure Ping_1367 expression levels at different temperatures (e.g., -12°C, 0°C, 5°C, 10°C) to determine if expression is upregulated at lower temperatures, which would suggest involvement in cold adaptation mechanisms.

• Gene knockout/complementation studies: Generate a Ping_1367 knockout strain of P. ingrahamii and assess growth capabilities at various temperatures compared to wild-type. Complementation with the wild-type gene should restore cold tolerance if the protein is critical.

• Heterologous expression analysis: Express Ping_1367 in a mesophilic host (e.g., E. coli) and evaluate whether it confers any enhanced cold tolerance.

• Protein-protein interaction studies: Utilize pull-down assays, co-immunoprecipitation, or two-hybrid systems adapted for low-temperature work to identify interaction partners that might elucidate Ping_1367's functional network.

• Structural studies at different temperatures: Apply circular dichroism, differential scanning calorimetry, and NMR to analyze temperature-dependent structural changes.

Implement a factorial experimental design approach rather than one-factor-at-a-time methods to efficiently explore multiple variables and potential interactions . This systematic approach enables researchers to understand how various factors (temperature, salinity, pH) might interact in affecting Ping_1367's function.

What expression systems are most effective for producing recombinant Ping_1367?

Based on successful approaches with other psychrophilic proteins, researchers should consider the following expression systems for Ping_1367:

• Pichia pastoris: This yeast system has been successfully used for expressing other proteins from P. ingrahamii, such as the nuclease PinNuc . It offers advantages for expressing eukaryotic post-translational modifications and often yields higher amounts of properly folded protein compared to bacterial systems.

• Cold-adapted E. coli strains: Modified E. coli strains that grow at lower temperatures (15-20°C) can improve folding of psychrophilic proteins. Consider using Arctic Express™ or similar strains co-expressing cold-adapted chaperonins.

• Psychrophilic host systems: For maintaining native folding and post-translational modifications, consider developing expression systems based on related Psychromonas species that can be grown at higher laboratory temperatures.

Optimization parameters should include:

• Induction temperature (typically much lower than standard protocols)

• Expression duration (often extended for cold-adapted systems)

• Media composition (may require additional osmoprotectants)

• Codon optimization for the expression host

Regardless of the chosen system, expression at reduced temperatures (10-15°C) is often critical for obtaining properly folded psychrophilic proteins, even though this results in slower growth and protein production rates.

What purification strategies are most effective for isolating Ping_1367?

Effective purification of recombinant Ping_1367 should incorporate strategies tailored to psychrophilic proteins:

• Low-temperature processing: Conduct all purification steps at 4°C or lower to maintain protein stability and native conformation.

• Affinity chromatography: Given that recombinant Ping_1367 will likely be produced with an affinity tag (as indicated in the product description where "tag type will be determined during production process" ), utilize appropriate affinity chromatography (His-tag, GST, etc.) as the initial capture step.

• Ion exchange chromatography: Based on the predicted isoelectric point calculated from the amino acid sequence, select appropriate ion exchange resins for further purification.

• Size exclusion chromatography: As a final polishing step to achieve high purity and remove aggregates that may form during earlier purification steps.

• Buffer optimization: For psychrophilic proteins, include cryoprotectants such as glycerol (10-20%) in purification buffers. Consider testing buffer systems with different ionic strengths, as the original organism grows in variable NaCl concentrations (1-10%) .

Monitor protein stability throughout purification using activity assays if available, or structural integrity assessments such as circular dichroism if the function is unknown. For membrane-associated proteins like Ping_1367 appears to be, consider including mild detergents in purification buffers to maintain solubility without denaturing the protein.

What are the recommended activity assays for characterizing Ping_1367 function?

Since UPF0316 proteins have unknown functions, a multi-faceted approach to functional characterization is recommended:

• Membrane association testing: Given the hydrophobic segments in Ping_1367's sequence, assess membrane binding through liposome association assays, using lipids extracted from P. ingrahamii or synthetic lipids mimicking psychrophilic membrane composition.

• Temperature-dependent binding assays: Examine potential interactions with nucleic acids, other proteins, or small molecules across a temperature gradient (-5°C to 25°C) to identify cold-specific binding properties.

• Structural stability assays: Monitor protein unfolding at different temperatures using differential scanning fluorimetry or circular dichroism to determine if Ping_1367 displays cold adaptation features like lower thermal stability and higher activity at low temperatures.

• Functional complementation: Test whether Ping_1367 can complement deletion of related UPF0316 family proteins in model organisms, observing phenotypic changes particularly related to cold tolerance.

• Proteomic approaches: Use proximity labeling methods such as BioID or APEX2 to identify interacting partners in vivo, which may provide clues to function.

When designing these assays, incorporate appropriate controls including:

• A mesophilic homolog of UPF0316 (if available)

• A heat-denatured negative control of Ping_1367

• Temperature controls spanning the growth range of P. ingrahamii (-12°C to 10°C)

How can structural studies of Ping_1367 contribute to understanding cold adaptation mechanisms?

Structural characterization of Ping_1367 can provide profound insights into cold adaptation mechanisms through:

These approaches would contribute significantly to the broader understanding of protein cold adaptation mechanisms while potentially revealing novel structural strategies employed by extremely psychrophilic organisms.

How might Ping_1367 be involved in the extreme cold tolerance of P. ingrahamii?

Based on the genomic analysis of P. ingrahamii and the protein's characteristics, several hypotheses can be proposed for Ping_1367's role in extreme cold tolerance:

• Membrane fluidity regulation: The hydrophobic regions in Ping_1367's sequence suggest potential membrane association . It could play a role in maintaining appropriate membrane fluidity at extremely low temperatures, perhaps by interacting with membrane lipids or other membrane proteins.

• Cold shock response: The protein may participate in the cellular response to temperature downshift, potentially acting as a cold sensor or signal transducer in cold shock response pathways.

• RNA/protein chaperoning: Many cold-adapted proteins function to prevent RNA secondary structure formation or protein misfolding at low temperatures. Ping_1367 might serve as a specialized cold chaperone for nucleic acids or proteins.

• Cryoprotectant interaction: P. ingrahamii produces extracellular polysaccharides as suggested by its high number of regulators of cyclic GDP . Ping_1367 could be involved in cryoprotectant production or regulation pathways.

Testing these hypotheses would require a combination of approaches including:

• Localization studies using fluorescently tagged Ping_1367

• Transcriptomic analysis comparing expression during steady-state growth vs. temperature downshift

• Interaction studies with membrane components and potential partner proteins

• Phenotypic analysis of knockout strains at varying temperatures

The protein's classification in the UPF0316 family indicates its function remains unknown, making it particularly intriguing as a potential novel mechanism for cold adaptation.

What comparative genomics approaches can reveal the evolutionary significance of Ping_1367?

To understand the evolutionary significance of Ping_1367 through comparative genomics, researchers should implement these approaches:

• Phylogenetic distribution analysis: Map the presence/absence of UPF0316 family proteins across psychrophilic, psychrotolerant, mesophilic, and thermophilic bacteria to determine if there's enrichment in cold-adapted organisms.

• Sequence conservation patterns: Analyze selection pressures on different regions of the protein using dN/dS ratios across homologs, identifying which regions are under purifying selection (functionally constrained) versus positive selection (potentially adapting to different thermal environments).

• Synteny analysis: Examine gene neighborhood conservation across species to identify potential functional associations through genomic context.

• Coevolution analysis: Identify proteins that show correlated evolutionary patterns with Ping_1367, suggesting functional interactions or participation in the same biological processes.

• Domain architecture comparison: Compare domain organization in UPF0316 homologs across temperature ranges to identify cold-specific architectural features.

This table presents potential findings and their implications:

These approaches would place Ping_1367 in an evolutionary context, potentially revealing whether it represents an ancestral trait or a specialized adaptation to the extreme cold environment inhabited by P. ingrahamii.

How can researchers address solubility issues when working with recombinant Ping_1367?

Psychrophilic proteins often present unique solubility challenges during recombinant expression. To address these issues with Ping_1367:

• Temperature optimization: Express at significantly lower temperatures (10-15°C) than typically used for recombinant proteins, even if this means extending expression times to 48-72 hours.

• Solubility tag selection: Test multiple solubility-enhancing tags including:

  • MBP (Maltose Binding Protein)

  • SUMO

  • TrxA (Thioredoxin)

  • NusA

• Buffer optimization matrix:

  Component	Range to Test	Rationale
  pH	6.0-8.5	Different from optimal growth pH
  NaCl	100-500 mM	Reflects natural environment variability
  Glycerol	5-20%	Cryoprotectant effect
  Mild detergents	0.1-1%	If membrane-associated
  Reducing agents	1-5 mM DTT or 5-10 mM β-ME	If protein contains cysteines

• Codon optimization: Optimize codons specifically for low-temperature expression in the chosen host, focusing on rare codons that might cause translational pausing and misfolding.

• Co-expression strategies: Co-express with cold-adapted chaperones like Cpn60/10 from psychrophilic organisms rather than standard chaperones.

If insolubility persists, consider native purification approaches under denaturing conditions followed by careful refolding at gradually decreasing temperatures to mimic the protein's natural folding environment.

What are common pitfalls in functional assays involving proteins from psychrophilic organisms?

When conducting functional assays with proteins from extreme psychrophiles like P. ingrahamii, researchers should be aware of these common pitfalls:

• Inappropriate temperature selection: Testing only at standard laboratory temperatures (20-37°C) rather than across the organism's growth range (-12°C to 10°C) . This may miss temperature-dependent activities or yield false negatives.

• Oxidation sensitivity: Many psychrophilic proteins, like the PinNuc nuclease from P. ingrahamii, are active only in their oxidized form and can be inactivated by reducing agents . Control redox conditions carefully during assays.

• Buffer composition mismatch: Using standard buffers optimized for mesophilic proteins rather than adapting ionic strength and composition to reflect the high salt environment of sea ice.

• Overlooking cold denaturation: Psychrophilic proteins may exhibit cold denaturation at temperatures that are still well above freezing, complicating low-temperature assays.

• Enzyme kinetics misinterpretation: Psychrophilic enzymes often display higher activity at low temperatures but lower thermostability. Ensure kinetic parameters (kcat, KM) are measured across appropriate temperature ranges with proper controls.

• Reference protein selection: Using mesophilic homologs as references without accounting for fundamental differences in stability and activity profiles.

To avoid these pitfalls, implement proper experimental design with appropriate controls, temperature ranges, and buffer conditions. Include time-course measurements to capture potentially slower reaction kinetics at lower temperatures, and consider developing specialized equipment for precise temperature control below 0°C.

How can researchers distinguish between temperature-dependent structural changes and functional changes in Ping_1367?

Differentiating between temperature-dependent structural changes and functional changes in Ping_1367 requires a methodical approach:

• Coupled structural-functional analysis: Simultaneously monitor structural parameters and functional outputs across a temperature gradient (-12°C to 25°C). This coupling allows direct correlation between specific structural transitions and functional outcomes.

• Site-directed mutagenesis coupled with thermal scanning: Identify temperature-sensitive regions through thermal scanning techniques, then create targeted mutations to determine their impact on both structure and function across temperatures.

• Ligand-induced stabilization: If ligands or binding partners are identified, compare temperature-dependent structural changes in their presence versus absence to distinguish functional binding sites from regions undergoing non-functional thermal transitions.

• Time-resolved measurements: Monitor the kinetics of structural changes versus functional changes during temperature shifts to establish cause-effect relationships.

• Domain isolation: Express and analyze individual domains to map temperature-dependent behavior to specific regions of the protein.

A practical experimental design would combine:

• Circular dichroism (CD) to monitor secondary structure

• Fluorescence spectroscopy to track tertiary structure changes

• Activity or binding assays for functional assessment

• Differential scanning calorimetry (DSC) to identify thermal transitions

Creating thermodynamic profiles that relate structure and function across temperatures will provide a comprehensive understanding of how Ping_1367 adapts to extreme cold while maintaining its functional role, whatever that may be.

What genomic engineering approaches could be used to study Ping_1367 in vivo?

Developing effective genomic engineering approaches for P. ingrahamii presents unique challenges due to its extreme growth conditions. Researchers should consider these methodologies:

• CRISPR-Cas9 system optimization: Adapt CRISPR-Cas9 components for function at low temperatures by:

  • Using Cas9 from psychrophilic organisms or engineering existing Cas9 for cold activity

  • Designing guide RNAs with reduced secondary structure formation at low temperatures

  • Optimizing promoters for expression under psychrophilic conditions

• Recombineering approaches: Develop λ-Red recombineering systems functional at low temperatures, potentially by expressing the recombination proteins under cold-inducible promoters from P. ingrahamii itself.

• Transposon mutagenesis: Employ transposon systems that function at low temperatures to generate a library of P. ingrahamii mutants for phenotypic screening.

• Conditional expression systems: Develop cold-regulated promoter systems to control Ping_1367 expression, allowing for the study of dosage effects without complete gene deletion.

• Fluorescent protein fusions: Optimize fluorescent proteins for proper folding and fluorescence at low temperatures to track Ping_1367 localization in vivo.

Implementation considerations should include extended incubation times to account for slower growth, maintenance of sterile conditions during long-term low-temperature incubations, and development of selective markers functional at extreme cold temperatures. Success with these approaches would significantly advance our ability to study the genetics of extreme psychrophiles and elucidate the in vivo function of Ping_1367.

How can knowledge about Ping_1367 contribute to biotechnological applications?

Understanding Ping_1367's structure and function can drive several biotechnological applications:

• Cold-active enzyme development: If Ping_1367 demonstrates enzymatic activity, its cold-adaptation features could be engineered into industrial enzymes for low-temperature applications, reducing energy requirements and enabling new process designs.

• Protein engineering principles: Structural insights from Ping_1367 could inform general design principles for engineering cold-activity into proteins, potentially identifying novel mechanisms beyond the currently known strategies.

• Cryopreservation technology: If Ping_1367 contributes to P. ingrahamii's extreme freeze tolerance, understanding its mechanism could lead to improved biological cryopreservation methods for cells, tissues, and organs.

• Biosensor development: Cold-active proteins like Ping_1367 could form the basis for biosensors functional at low temperatures for environmental monitoring in polar regions or cold storage facilities.

• Expression system enhancement: Knowledge of how Ping_1367 maintains functionality at low temperatures could inform the development of improved cold-expression systems for recombinant protein production, addressing a significant biotechnological challenge.