Recombinant Aquifex aeolicus Uncharacterized protein aq_1900 (aq_1900)

What is Aquifex aeolicus Uncharacterized protein aq_1900?

Aq_1900 is a protein from the hyperthermophilic bacterium Aquifex aeolicus with currently unknown function. The full-length protein consists of 168 amino acids and has been assigned the UniProt ID O67738. While its specific cellular role remains uncharacterized, sequence analysis suggests potential membrane association based on its hydrophobic regions. The protein can be recombinantly expressed in E. coli systems with an N-terminal His-tag for purification purposes. As a protein from an extremophile organism that thrives at temperatures above 85°C, aq_1900 may possess unusual thermostability and potentially unique functional properties that could provide insights into extremophile biology or reveal novel enzymatic activities that function under extreme conditions .

What are the basic properties of recombinant aq_1900 protein?

The recombinant form of aq_1900 is typically expressed in E. coli with an N-terminal His-tag and has the following properties:

The amino acid sequence contains hydrophobic regions, suggesting potential membrane association or transmembrane domains that may be critical for its native function .

How should recombinant aq_1900 be stored and reconstituted?

Proper storage and reconstitution are essential for maintaining the activity and stability of recombinant aq_1900. According to product specifications, the following protocol is recommended:

• Storage conditions: Store the lyophilized powder at -20°C/-80°C upon receipt. Aliquoting is necessary for multiple use to avoid repeated freeze-thaw cycles.

• Reconstitution procedure:

  • Briefly centrifuge the vial prior to opening to bring the contents to the bottom

  • Reconstitute the protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL

  • For long-term storage, add 5-50% glycerol (final concentration) and prepare aliquots

  • Store aliquots at -20°C/-80°C

• Working stock: Working aliquots can be stored at 4°C for up to one week, but repeated freezing and thawing is not recommended as it may affect protein stability and activity .

What expression systems are most effective for producing recombinant aq_1900?

Escherichia coli is the primary expression system utilized for recombinant production of aq_1900. The T7 promoter system present in pET vectors (pMB1 origin, medium copy number) is particularly effective, as it can yield target protein representing up to 50% of the total cell protein in successful cases . This system employs bacteriophage T7 RNA polymerase, which is highly selective for its cognate promoter, allowing for controlled and high-level expression.

For thermostable proteins from extremophiles like Aquifex aeolicus, E. coli expression offers several advantages:

• Recombinant proteins can often be purified through heat treatment steps that denature most E. coli proteins while leaving the thermostable target protein intact

• High yield production can be achieved in standard laboratory conditions

• Well-established genetic tools allow for optimization of expression parameters

How can vesicle-packaging technology improve aq_1900 production?

An innovative system using a short peptide tag that exports recombinant proteins in membrane-bound vesicles from E. coli provides an effective solution to various challenges associated with bacterial recombinant protein expression, particularly for proteins like aq_1900 with potential membrane association. This vesicle-based technology offers several significant advantages:

• Compartmentalization: The vesicles create micro-environments that facilitate the production of otherwise challenging proteins, including those that are toxic, insoluble, or contain disulfide bonds.

• Increased yield: Protein yield is substantially increased when compared to typical bacterial expression without the vesicle-nucleating peptide tag.

• Simplified isolation: The release of vesicle-packaged proteins supports isolation directly from the culture medium, potentially simplifying downstream processing.

• Enhanced storage stability: The vesicle packaging permits long-term active protein storage, maintaining functionality better than traditional storage methods.

• Native-like environment: For membrane-associated proteins like aq_1900, the lipid bilayer environment of vesicles may promote proper folding and function.

This technology could be particularly valuable for aq_1900 expression if initial attempts at conventional expression yield poor results or if the protein shows evidence of membrane interaction .

What purification strategies are most effective for aq_1900?

Given that recombinant aq_1900 is typically expressed with an N-terminal His-tag, immobilized metal affinity chromatography (IMAC) serves as the primary purification method. A comprehensive purification strategy would include:

• Cell lysis: Bacterial cells expressing aq_1900 can be disrupted using sonication, French press, or chemical lysis in the presence of appropriate protease inhibitors to prevent degradation.

• Heat treatment (optional): As aq_1900 is derived from a hyperthermophilic organism, a heat treatment step (e.g., 70-80°C for 15-20 minutes) can be employed to denature most E. coli proteins while preserving the thermostable target protein.

• IMAC purification:

  • Clarify the lysate by centrifugation (15,000-20,000 × g for 30 minutes)

  • Load the clarified lysate onto a Ni-NTA or similar resin

  • Wash with low concentrations of imidazole (20-50 mM) to remove non-specifically bound proteins

  • Elute aq_1900 with higher imidazole concentrations (250-500 mM)

• Secondary purification: Size exclusion chromatography (SEC) can be employed to achieve higher purity and remove aggregates.

• Buffer exchange: Dialysis or desalting columns can be used to remove imidazole and exchange into the storage buffer (Tris/PBS-based buffer with 6% Trehalose, pH 8.0).

For membrane-associated proteins like aq_1900 appears to be, inclusion of appropriate detergents throughout the purification process may be necessary to maintain solubility and proper folding .

How can Design of Experiments (DoE) optimize aq_1900 expression conditions?

Design of Experiments (DoE) offers a systematic approach to optimize aq_1900 expression by efficiently testing multiple factors simultaneously, rather than the less efficient one-factor-at-a-time approach. A comprehensive DoE strategy for aq_1900 expression would include:

• Factor identification: Key factors affecting expression typically include:

  • Temperature (20-37°C)

  • Inducer concentration (e.g., IPTG at 0.1-1.0 mM)

  • Induction time (3-24 hours)

  • Media composition (LB, TB, 2×YT, defined media)

  • Cell density at induction (OD600 0.4-1.0)

  • Additives (e.g., glucose, glycerol)

  • Aeration levels

• Design selection: For initial screening with 4 or more factors, fractional factorial designs or Plackett-Burman designs significantly reduce the experimental burden. For example, with 7 factors, a full factorial design would require 2^7 = 128 runs, whereas screening designs might require only 8-16 experiments.

• Response measurement: Clear metrics should be established to evaluate expression success, such as:

  • Total protein yield (mg/L culture)

  • Soluble fraction percentage

  • Functional activity (if an assay is available)

  • Purity after initial capture step

• Analysis: Statistical software can analyze results to identify significant factors and interactions, generating a predictive model of expression conditions.

• Optimization: Once significant factors are identified, response surface methodology (RSM) can fine-tune conditions to maximize protein yield and quality.

This systematic approach is particularly valuable for challenging proteins like aq_1900, where optimal expression conditions may not be intuitive4.

What structural characterization approaches are suitable for aq_1900?

Given the uncharacterized nature and potential membrane association of aq_1900, a multi-faceted structural characterization approach is recommended:

For membrane-associated proteins like aq_1900 may be, special considerations include using detergents, lipid nanodiscs, or amphipols for stabilization during structural studies .

What bioinformatic approaches can predict aq_1900 function?

Despite being uncharacterized, several complementary bioinformatic approaches can generate hypotheses about aq_1900's potential function:

• Sequence-based analyses:

  • Homology detection using PSI-BLAST, HHpred, or HMMER against protein databases

  • Conserved domain analysis using CDD, Pfam, or InterPro

  • Motif scanning using PROSITE or ELM to identify functional motifs

  • Transmembrane domain prediction using TMHMM, Phobius, or TOPCONS

  • Signal peptide prediction using SignalP

• Structure-based predictions:

  • Protein structure prediction using AlphaFold2 or RoseTTAFold

  • Structural alignment against known protein structures using DALI or TM-align

  • Binding site prediction using CASTp, FTSite, or SiteMap

  • Molecular docking with potential ligands based on structural similarity

• Genomic context analysis:

  • Gene neighborhood analysis in Aquifex aeolicus and related organisms

  • Co-expression patterns if transcriptomic data is available

  • Phylogenetic profiling to identify co-evolving genes

• Integration of experimental and computational data:

  • Comparison of predicted properties with experimental observations

  • Refinement of hypotheses based on initial functional assays

  • Iterative approach combining experimental testing with computational refinement

A comprehensive workflow would begin with broad sequence-based analyses, followed by more specific structural predictions and experimental validation of the most promising hypotheses .

How does His-tagging affect aq_1900 structure and function?

The addition of a His-tag to aq_1900, while essential for purification, may influence protein structure and function in several ways that researchers should consider:

• Potential structural impacts:

  • N-terminal tags may alter protein folding kinetics or final conformation

  • Tags can potentially interfere with oligomerization or protein-protein interactions

  • For membrane-associated proteins like aq_1900, tags may affect membrane insertion or orientation

• Functional considerations:

  • His-tags may influence enzymatic activity, especially if located near active sites

  • The charged nature of His-tags can alter protein-substrate interactions

  • Tags may affect protein stability, particularly under extreme conditions relevant to a thermophilic protein

• Mitigation strategies:

  • Incorporate cleavable linkers (e.g., TEV protease site) between the tag and protein

  • Compare properties of tagged and untagged versions after protease cleavage

  • Consider both N- and C-terminal tagging to determine optimal configuration

  • Use longer linkers to distance the tag from the protein

• Experimental validation:

  • Circular dichroism to compare secondary structure of tagged vs. untagged protein

  • Thermal stability assays to assess if tagging affects thermostability

  • Activity assays (once a function is identified) with both tagged and untagged versions

For aq_1900 specifically, the commercial preparation uses an N-terminal His-tag, suggesting this position is less likely to interfere with function, but careful validation remains important for detailed characterization studies .

How can potential membrane association of aq_1900 be experimentally verified?

The amino acid sequence of aq_1900 suggests potential membrane association, which can be verified through several complementary experimental approaches:

• Membrane fractionation studies:

  • Separate bacterial membranes from cytosolic fractions using ultracentrifugation

  • Analyze protein distribution between fractions using Western blotting

  • Further separate inner and outer membranes to determine specific localization

• Microscopy techniques:

  • Fluorescence microscopy with GFP-tagged aq_1900 to visualize cellular localization

  • Immunogold electron microscopy for higher resolution localization

  • Super-resolution microscopy to determine precise membrane association patterns

• Membrane interaction assays:

  • Liposome binding assays with purified aq_1900

  • Detergent solubility screens to assess membrane protein characteristics

  • Membrane protein extraction methods using different detergents

• Structural approaches:

  • Circular dichroism in the presence and absence of membrane-mimetic environments

  • NMR studies with membrane mimetics (micelles, bicelles, nanodiscs)

  • Hydrogen-deuterium exchange mass spectrometry to identify membrane-protected regions

• Computational validation:

  • Hydropathy analysis and transmembrane domain prediction

  • Molecular dynamics simulations in membrane environments

  • Comparison with known membrane proteins from similar organisms

These methods provide complementary information about aq_1900's potential membrane association, from cellular localization to specific lipid interactions .

What approaches can determine the thermostability properties of aq_1900?

As a protein from the hyperthermophilic bacterium Aquifex aeolicus, aq_1900 likely possesses significant thermostability that can be characterized through several experimental approaches:

• Thermal denaturation studies:

  • Differential scanning calorimetry (DSC) to determine melting temperature (Tm)

  • Circular dichroism (CD) spectroscopy with temperature ramping to monitor secondary structure changes

  • Fluorescence-based thermal shift assays using environment-sensitive dyes

  • Intrinsic tryptophan fluorescence monitoring during thermal denaturation

• Activity-based stability assessments:

  • Incubation at various temperatures followed by residual activity measurement

  • Real-time activity monitoring at elevated temperatures

  • Comparative activity profiling against mesophilic homologs (if identified)

• Structural stability analyses:

  • Limited proteolysis at different temperatures to assess conformational rigidity

  • Hydrogen-deuterium exchange mass spectrometry at various temperatures

  • X-ray crystallography at room and elevated temperatures

  • Molecular dynamics simulations at different temperatures

• Stability under different conditions:

  • pH stability profile in combination with temperature

  • Chemical denaturation combined with thermal challenges

  • Long-term stability studies at elevated temperatures

The data from these studies can be compiled into a comprehensive thermostability profile that characterizes the unique properties of aq_1900 and may provide insights into structural features contributing to thermostability in proteins from hyperthermophilic organisms .

What systematic approaches can identify potential ligands or binding partners for aq_1900?

Without prior knowledge of aq_1900's function, a systematic approach to identify potential ligands or binding partners is essential:

• Thermal shift assays (differential scanning fluorimetry):

  • Screen compound libraries to identify molecules that alter protein thermal stability

  • Test metabolite collections, cofactors, metal ions, and nucleotides

  • Analyze concentration-dependent effects of initial hits

• Affinity-based methods:

  • Pull-down assays using immobilized His-tagged aq_1900 as bait

  • Cross-linking mass spectrometry to capture transient interactions

  • Surface plasmon resonance (SPR) screening against candidate molecules

  • Isothermal titration calorimetry (ITC) for thermodynamic characterization of binding

• Activity-based approaches:

  • Generic enzymatic activity assays for common reaction types

  • Substrate profiling using diverse compound libraries

  • Activity-based protein profiling with reactive probes

• Structural methods:

  • Fragment-based screening by NMR or X-ray crystallography

  • Computational docking of virtual compound libraries

  • Hydrogen-deuterium exchange mass spectrometry to identify binding-induced conformational changes

• Cellular approaches:

  • Yeast two-hybrid or bacterial two-hybrid screening

  • Co-immunoprecipitation from native or heterologous expression systems

  • Proximity-dependent labeling approaches (BioID, APEX)

This multi-faceted approach increases the likelihood of identifying physiologically relevant ligands or binding partners, providing crucial insights into aq_1900's function .

What challenges might researchers face when working with aq_1900 and how can they be addressed?

Working with an uncharacterized protein from a hyperthermophilic organism presents several unique challenges:

• Expression and solubility issues:

  • Challenge: Codon usage differences between A. aeolicus and E. coli

  • Solution: Use codon-optimized synthetic genes or E. coli strains with rare tRNAs

  • Challenge: Potential membrane association leading to insolubility

  • Solution: Vesicle-packaging expression systems that compartmentalize proteins within a micro-environment, facilitating the production of otherwise challenging proteins

• Purification difficulties:

  • Challenge: Potential for inclusion body formation

  • Solution: Optimize expression conditions using Design of Experiments (DoE) approaches4

  • Challenge: Co-purification of E. coli contaminants

  • Solution: Utilize the thermostability of aq_1900 through heat treatment steps that denature E. coli proteins

• Functional characterization:

  • Challenge: Unknown function makes assay design difficult

  • Solution: Employ systematic screening approaches and bioinformatic predictions

  • Challenge: Potential requirement for extreme conditions for activity

  • Solution: Develop specialized assay conditions that mimic the native environment of A. aeolicus

• Structural studies:

  • Challenge: Membrane proteins are challenging for crystallography

  • Solution: Consider alternative structural approaches like cryo-EM or NMR with membrane mimetics

• Physiological relevance:

  • Challenge: Difficulty in establishing biological context without genetic tools for A. aeolicus

  • Solution: Use comparative genomics and heterologous expression studies in model organisms

By anticipating these challenges and implementing appropriate strategies, researchers can enhance their chances of successfully characterizing this interesting protein from an extremophile organism 4.

How can comparative analysis with other extremophile proteins enhance understanding of aq_1900?

Comparative analysis with other proteins from extremophiles provides valuable context for understanding aq_1900:

• Sequence-based comparative approaches:

  • Identify homologs in other extremophiles using sensitive sequence search methods (PSI-BLAST, HHpred)

  • Construct multiple sequence alignments to identify conserved residues potentially critical for function

  • Perform phylogenetic analysis to understand evolutionary relationships

  • Compare amino acid composition patterns with other extremophile proteins (e.g., increased charged residues in thermophiles)

• Structural comparison:

  • Analyze common structural adaptations in proteins from hyperthermophiles

  • Identify potential stabilizing features (disulfide bonds, salt bridges, compact hydrophobic cores)

  • Compare predicted or determined structures with known extremophile protein structures

• Genomic context analysis:

  • Examine conservation of genomic neighborhood across related organisms

  • Identify if aq_1900 is part of an operon that may suggest functional relationships

  • Analyze co-occurrence patterns with other genes across diverse extremophiles

• Functional insights:

  • If homologs with known functions exist in other extremophiles, use this information to guide functional hypotheses

  • Compare expression patterns under different stress conditions if transcriptomic data is available

  • Examine patterns of evolutionary conservation in potential binding sites or catalytic regions

This comparative approach can provide insights into both the potential function of aq_1900 and its role in extremophile adaptation, potentially revealing conserved mechanisms for protein stability under extreme conditions .