Recombinant Staphylococcus aureus UPF0365 protein SaurJH1_1665 (SaurJH1_1665)

What is the UPF0365 protein SaurJH1_1665?

The UPF0365 protein SaurJH1_1665 is a hypothetical protein from Staphylococcus aureus strain JH1, classified in the UPF0365 family of proteins with unknown function. Its full amino acid sequence begins with MFSLSFIVIAVIIIVALLILFSFVPIGLWISALAAGVHVGIGTLVGMRLRRVSPRKVIAP and continues through 329 amino acids . The protein is designated with UniProt accession number A6U245 . The "hypothetical" classification indicates that its existence is predicted based on genomic sequence analysis, but its biological function remains uncharacterized. The protein appears to have transmembrane domains based on the hydrophobic stretches in its N-terminal sequence, suggesting potential membrane localization .

Sequence analysis indicates that homologs of this protein exist across various Staphylococcus strains, including the SAHV_1560 variant noted in the literature . Research approaches typically focus on comparative genomics, structural predictions, and experimental characterization to elucidate the function of such uncharacterized proteins.

What are the recommended storage conditions for recombinant SaurJH1_1665?

For optimal stability of recombinant SaurJH1_1665 protein, storage at -20°C is recommended for routine use, while long-term storage should be at -20°C or -80°C . The protein is typically supplied in a liquid formulation containing glycerol, which acts as a cryoprotectant to prevent protein denaturation during freeze-thaw cycles .

To minimize protein degradation, it is strongly advised to avoid repeated freezing and thawing of stock solutions . When actively working with the protein, prepare small working aliquots that can be stored at 4°C for up to one week . This aliquoting strategy significantly reduces the need for multiple freeze-thaw cycles of the main stock, thereby preserving the structural and functional integrity of the protein over time.

For researchers conducting extended studies, implementing a proper inventory system to track the number of freeze-thaw cycles each aliquot has undergone is recommended as part of good laboratory practice to maintain experimental consistency and reproducibility.

What expression systems are used for SaurJH1_1665 production?

For researchers requiring proteins with specific modifications or struggling with solubility in E. coli, alternative expression systems should be considered. Yeast systems offer a eukaryotic environment with moderate post-translational modification capabilities, while insect cell (baculovirus) and mammalian cell systems provide more complex modification patterns that may better reflect the protein's native state in certain experimental contexts .

How is the purity of recombinant SaurJH1_1665 typically assessed?

The purity of recombinant SaurJH1_1665 is typically assessed using multiple complementary analytical techniques. Commercial preparations generally target >90% purity as indicated in product specifications . The primary methods for purity assessment include:

• SDS-PAGE (Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis) with Coomassie blue staining, which provides visual confirmation of protein size and relative purity.

• Western blotting using tag-specific antibodies (such as anti-His antibodies for His-tagged variants) to confirm protein identity and assess degradation products .

• Size-exclusion chromatography (SEC) to evaluate protein aggregation and oligomeric state.

• Mass spectrometry for precise molecular weight determination and detection of post-translational modifications or truncations.

For research applications requiring exceptional purity, additional methods such as reversed-phase HPLC may be employed. Researchers should verify the batch-specific purity information provided by manufacturers and consider performing their own quality control analysis before critical experiments, especially when investigating novel functions of this hypothetical protein.

What experimental approaches are suitable for studying hypothetical proteins like SaurJH1_1665?

Investigating hypothetical proteins such as SaurJH1_1665 requires a multifaceted experimental approach that combines computational predictions with experimental validation. A comprehensive research strategy should include:

• Comparative genomics and phylogenetic analysis to identify conserved domains and evolutionary relationships with proteins of known function. This can be particularly valuable for UPF0365 family proteins across different Staphylococcus strains .

• Structural studies using X-ray crystallography, NMR spectroscopy, or cryo-electron microscopy to determine three-dimensional structure, which often provides critical insights into function.

• Protein-protein interaction studies using techniques such as pull-down assays, co-immunoprecipitation, or yeast two-hybrid screening to identify potential binding partners that may suggest functional pathways .

• Gene knockout or knockdown studies in S. aureus to observe phenotypic changes that might reveal the protein's role in bacterial physiology or pathogenesis.

• Heterologous expression followed by functional assays testing various biochemical activities (e.g., enzymatic activity, DNA/RNA binding, or lipid interaction) based on structural predictions.

True experimental research designs incorporating appropriate controls are essential for studying hypothetical proteins . For instance, a posttest-only control group design could compare wild-type S. aureus with a SaurJH1_1665 knockout strain under various stress conditions to identify phenotypic differences .

How do tags affect the functionality of SaurJH1_1665?

Tags, such as the His-tag frequently used with recombinant SaurJH1_1665 , can significantly impact protein functionality through several mechanisms that researchers must consider:

• Structural interference: Tags may alter protein folding or interfere with active sites, particularly if positioned near functionally important regions. For membrane-associated proteins like SaurJH1_1665 with its hydrophobic N-terminus, N-terminal tags might disrupt membrane insertion and localization .

• Solubility effects: While tags like His-6 can improve protein solubility during purification, they may also artificially enhance the solubility of proteins that would naturally exist in membrane-bound or less soluble states, potentially masking native characteristics.

• Oligomerization influence: Tags can either promote or inhibit protein-protein interactions, potentially affecting the oligomeric state of SaurJH1_1665 and giving misleading results in interaction studies.

For rigorous functional characterization, comparing the behavior of tagged and tag-cleaved versions of SaurJH1_1665 is recommended. Many expression constructs include protease recognition sites between the tag and the protein of interest, allowing tag removal after purification. Additionally, comparing N-terminal versus C-terminal tagged variants can help identify position-dependent effects, particularly important for proteins with predicted membrane domains like SaurJH1_1665 .

What are the optimal buffer conditions for functional studies?

Determining optimal buffer conditions for functional studies of SaurJH1_1665 requires systematic testing, as no universal conditions exist for all proteins. Based on available information and general principles for membrane-associated bacterial proteins, consider the following parameters:

• Buffer composition: Tris-based buffers are commonly used for initial storage of SaurJH1_1665 . For functional studies, phosphate buffers (pH 7.0-7.5) often better mimic physiological conditions of Staphylococcus aureus.

• pH range: Testing a pH series from 6.0-8.0 is recommended, with closer increments around pH 7.2-7.4 to approximate bacterial cytoplasmic conditions.

• Salt concentration: NaCl concentrations between 50-300 mM should be evaluated, as membrane proteins often require higher ionic strength for stability.

• Glycerol content: While storage formulations contain 50% glycerol , functional assays typically reduce this to 5-10% to minimize viscosity effects while maintaining protein stability.

• Detergent selection: For a predicted membrane protein like SaurJH1_1665, mild non-ionic detergents (0.01-0.1% n-dodecyl-β-D-maltoside or 0.5-1% CHAPS) may be necessary to maintain native conformation.

A systematic buffer optimization approach using techniques like differential scanning fluorimetry (thermal shift assays) can rapidly identify conditions that maximize protein stability. For activity assays, researchers should establish a baseline buffer and methodically vary components while monitoring functionality markers.

How does SaurJH1_1665 compare to homologous proteins in other Staphylococcus strains?

SaurJH1_1665 belongs to the UPF0365 protein family found across multiple Staphylococcus strains, with notable homologs including SAHV_1560 from another S. aureus strain . Comparative analysis reveals:

For comprehensive comparative studies, researchers should align sequences from multiple clinical and laboratory S. aureus strains to identify highly conserved residues that likely serve critical functions. Additionally, examining UPF0365 homologs in more distantly related Staphylococcus species and other Gram-positive bacteria could reveal evolutionary patterns that suggest functional importance in bacterial physiology or pathogenesis.

What are the potential interaction partners of SaurJH1_1665?

While specific interaction partners of SaurJH1_1665 have not been definitively established in the available literature , several approaches can be employed to identify potential protein-protein interactions:

• Bioinformatic prediction: Using tools that analyze co-evolution patterns, shared expression profiles, and genomic context to predict functional associations. The genomic neighborhood of SaurJH1_1665 may contain genes whose products functionally interact with this protein.

• Affinity purification-mass spectrometry (AP-MS): This technique involves using tagged SaurJH1_1665 as bait to capture interacting proteins from S. aureus lysates, followed by mass spectrometric identification.

• Bacterial two-hybrid systems: These provide an in vivo approach to detect protein interactions by linking them to transcriptional activation of reporter genes.

• Cross-linking studies: Chemical cross-linking combined with mass spectrometry can capture transient interactions that might be missed by other techniques.

• Surface plasmon resonance (SPR) or bio-layer interferometry (BLI): These biophysical techniques can validate predicted interactions and determine binding affinities.

Based on the predicted membrane localization of SaurJH1_1665 , potential interaction partners may include other membrane proteins involved in cell wall synthesis, membrane transport, or signaling pathways. Additionally, proteins involved in stress response or virulence factor regulation should be considered, as many hypothetical proteins in pathogenic bacteria ultimately contribute to these functions.

What are the appropriate controls for experiments involving SaurJH1_1665?

Designing robust controls is essential for experiments involving hypothetical proteins like SaurJH1_1665. Following true experimental research principles , researchers should implement these controls:

• Negative controls:

  • Empty vector controls in expression studies to account for host cell responses

  • Purified irrelevant protein of similar size/properties for binding studies

  • Isogenic knockout strains without complementation for phenotypic studies

  • Heat-denatured SaurJH1_1665 to distinguish between specific and non-specific effects

• Positive controls:

  • Well-characterized membrane proteins when studying localization

  • Known protein-protein interaction pairs when establishing interaction assays

  • Reference genes/proteins from the same family with established functions

• Technical controls:

  • Tag-only constructs to assess tag-specific artifacts

  • Multiple tag positions (N-terminal vs. C-terminal) to identify position-dependent effects

  • Expression level controls to ensure phenotypes aren't due to protein overexpression

• Experimental design controls:

  • Implementation of the Solomon four-group design when appropriate, which includes all permutations of control and experimental groups with both pretest and posttest measurements

  • Randomized group assignment to eliminate selection bias

  • Blinded analysis of results to prevent observer bias

These comprehensive controls help distinguish genuine biological functions from experimental artifacts, particularly important when studying proteins of unknown function where expected outcomes are not well defined.

How can the subcellular localization of SaurJH1_1665 be determined?

Determining the subcellular localization of SaurJH1_1665 is crucial for understanding its function, particularly given its predicted membrane-associated domains . A multi-method approach should be employed:

• Computational prediction: Begin with algorithms specifically designed for bacterial proteins (such as PSORTb, CELLO, or SignalP) to predict localization based on sequence features like signal peptides, transmembrane domains, and sorting signals.

• Fluorescent protein fusions: Generate constructs expressing SaurJH1_1665 fused to fluorescent proteins (e.g., GFP or mCherry) for visualization in live cells using fluorescence microscopy. For membrane proteins, careful consideration of fusion orientation is essential to prevent disruption of targeting signals.

• Subcellular fractionation: Separate bacterial cellular components (cytoplasm, membrane, cell wall, extracellular fractions) followed by Western blot analysis using antibodies against the protein or its tag. Compare distribution patterns with known markers for each fraction.

• Immunoelectron microscopy: Use gold-labeled antibodies against SaurJH1_1665 or its tag for high-resolution localization within fixed bacterial cells.

• Protease accessibility assays: Expose intact cells, spheroplasts, or membrane vesicles to proteases to determine which regions of the protein are accessible, providing topological information for membrane proteins.

Implementing a quasi-experimental research design allows comparison of localization patterns under different conditions (e.g., growth phases, stress conditions) that might reveal dynamic changes in protein distribution, potentially providing functional insights.

What methods are recommended for assessing SaurJH1_1665 solubility?

Assessing the solubility of SaurJH1_1665 requires carefully designed experiments that account for its predicted membrane-associated nature . Recommended methodological approaches include:

• Expression screening in multiple systems: Test parallel expressions in E. coli, yeast, and cell-free systems with varying induction conditions (temperature, inducer concentration, duration) to identify optimal solubility conditions .

• Detergent screening: Systematically evaluate a panel of detergents (non-ionic, zwitterionic, and mild ionic) at various concentrations for their ability to solubilize SaurJH1_1665 from membrane fractions while maintaining protein integrity.

• Quantitative solubility assessment:

  • Ultracentrifugation-based separation of soluble and insoluble fractions

  • SDS-PAGE and Western blot analysis to quantify distribution between fractions

  • Light scattering techniques to detect aggregation in solution

• Fusion partner approach: Test the effect of solubility-enhancing fusion partners (MBP, SUMO, thioredoxin) on expression outcomes, comparing with standard tag systems like His-tags .

• Structure-guided engineering: Based on computational predictions of hydrophobic regions, design constructs that exclude predicted transmembrane domains while preserving soluble domains for functional studies.

Data should be presented quantitatively, reporting the percentage of total expressed protein recovered in the soluble fraction under each condition tested. This methodical approach allows researchers to optimize conditions for subsequent functional and structural studies.

How can post-translational modifications of SaurJH1_1665 be analyzed?

While bacterial proteins typically undergo fewer post-translational modifications (PTMs) than eukaryotic proteins, several potential modifications could affect SaurJH1_1665 function. A comprehensive analytical approach includes:

• Mass spectrometry-based PTM mapping:

  • Bottom-up proteomics: Enzymatic digestion followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS)

  • Top-down proteomics: Analysis of intact protein to preserve modification patterns

  • Targeted approaches using selected reaction monitoring (SRM) for specific modifications

• Key modifications to investigate:

  • Phosphorylation: Particularly on serine, threonine, and tyrosine residues

  • Acetylation: Often occurring at lysine residues

  • Methylation: On lysine and arginine residues

  • Lipidation: Especially relevant for membrane-associated proteins like SaurJH1_1665

  • Signal peptide cleavage: Critical for determining the mature protein's N-terminus

• Enrichment strategies:

  • Phosphopeptide enrichment using titanium dioxide or immobilized metal affinity chromatography

  • Antibody-based enrichment for acetylated or methylated residues

  • Chemical labeling approaches for specific modifications

• Functional validation:

  • Site-directed mutagenesis of identified modification sites

  • Comparison of PTM patterns between different growth conditions

  • In vitro modification assays with purified modifying enzymes

Presenting PTM data requires detailed mapping to the protein sequence with statistical confidence measures for each identified modification site. When possible, quantitative comparison of modification levels between different experimental conditions provides valuable functional insights.

What experimental designs best address the challenges in studying hypothetical proteins?

Studying hypothetical proteins like SaurJH1_1665 presents unique challenges that require specialized experimental designs. Based on established research methodology , the following approaches are recommended:

• Integrative "function discovery" pipeline:

  • Begin with computational predictions (structural modeling, sequence analysis)

  • Validate predictions with targeted biochemical assays

  • Scale to systems-level analyses (transcriptomics, proteomics)

  • Confirm biological relevance with in vivo studies

• True experimental research designs with randomization :

  • Solomon four-group design for phenotypic studies, incorporating pretest and posttest measurements with proper controls

  • Posttest-only control group design for initial screening of potential functions

  • Factorial experimental designs to simultaneously test multiple variables

• Comparative experimental approaches:

  • Parallel analysis of SaurJH1_1665 and its homologs from other strains (e.g., SAHV_1560)

  • Cross-species complementation studies to test functional conservation

  • Domain swapping experiments between related proteins

• Unbiased screening strategies:

  • Chemical genetic screening to identify conditions where SaurJH1_1665 becomes essential

  • Synthetic genetic arrays to map genetic interactions

  • Phenotypic microarrays to identify conditions affecting growth of knockout strains

• Temporal and conditional expression studies:

  • Regulated expression systems to control protein levels

  • Time-course experiments during infection or stress response

  • Host-pathogen interaction models to assess virulence contributions

These designs should incorporate appropriate statistical power calculations to ensure meaningful results, particularly important when expected effect sizes are unknown for hypothetical proteins .

How can protein degradation of SaurJH1_1665 be minimized?

Preventing degradation of SaurJH1_1665 during purification and storage requires a systematic approach addressing multiple potential degradation pathways:

• Expression and purification optimization:

  • Reduce expression temperature (16-25°C) to slow production and improve folding

  • Use protease-deficient host strains for expression

  • Include protease inhibitor cocktails throughout purification

  • Minimize purification duration with efficient protocols

• Storage condition refinement:

  • Implement the recommended storage at -20°C or -80°C for long-term stability

  • Maintain glycerol concentration at 50% as specified in commercial preparations

  • Aliquot into single-use volumes to avoid repeated freeze-thaw cycles

  • Store working aliquots at 4°C for maximum of one week

• Buffer optimization:

  • Identify stabilizing additives through thermal shift assays

  • Test stabilizing agents like trehalose or sucrose as cryoprotectants

  • Optimize pH to minimize acid/base-catalyzed hydrolysis

  • Include reducing agents (DTT, TCEP) if cysteine oxidation is problematic

• Analytical monitoring:

  • Implement regular quality control by SDS-PAGE to detect degradation products

  • Use size-exclusion chromatography to monitor aggregation

  • Apply mass spectrometry to identify specific degradation sites

Systematic documentation of storage conditions, freeze-thaw cycles, and degradation patterns enables correlation analysis to identify critical factors affecting SaurJH1_1665 stability. This methodical approach allows researchers to develop optimal handling protocols specific to this protein.

What are the common challenges in expressing full-length SaurJH1_1665?

Expression of full-length SaurJH1_1665 (329 amino acids) presents several challenges typical of membrane-associated bacterial proteins:

• Toxicity to expression hosts:

  • Membrane protein overexpression can disrupt host cell membrane integrity

  • Solution: Use tightly regulated expression systems with inducible promoters

  • Test lower induction levels (reduced inducer concentration, shorter induction times)

  • Consider specialized E. coli strains (C41/C43) designed for toxic protein expression

• Codon usage disparities:

  • S. aureus codon bias differs from E. coli, potentially causing translational stalling

  • Solution: Use codon-optimized synthetic genes for the expression host

  • Alternative: Express in E. coli Rosetta strains supplying rare tRNAs

• Protein folding issues:

  • Hydrophobic regions (particularly the N-terminal sequence) may cause misfolding

  • Solution: Express with folding-enhancing fusion partners (MBP, SUMO)

  • Reduce expression temperature (16-20°C) to slow folding

  • Co-express with chaperones (GroEL/ES, DnaK systems)

• Truncation products:

  • Internal translation initiation or premature termination

  • Solution: Optimize ribosome binding sites

  • Use C-terminal tags to ensure only full-length protein is purified

  • Western blot analysis with antibodies targeting different protein regions

• Membrane integration challenges:

  • Test expression in systems with different membrane compositions

  • Consider using cell-free expression systems with supplied lipids/detergents

Systematic optimization using a factorial experimental design approach allows efficient identification of optimal expression conditions for full-length SaurJH1_1665, minimizing time spent on sequential optimization of individual parameters.

How can activity loss during storage be prevented?

Preventing activity loss of SaurJH1_1665 during storage requires both proper storage conditions and activity monitoring strategies:

• Storage condition optimization beyond basic recommendations:

  • While general storage at -20°C or -80°C in 50% glycerol is recommended , activity-specific conditions may require refinement

  • Test activity retention in different buffer systems (HEPES, phosphate, Tris)

  • Evaluate pH stability range through activity measurements after storage at different pH values

  • Assess the impact of various stabilizing additives (amino acids, sugars, specific ions)

• Cryoprotectant strategies:

  • Compare activity retention with different cryoprotectants (glycerol, sucrose, trehalose)

  • Test protein stability in the absence of cryoprotectants when flash-frozen in liquid nitrogen

  • Evaluate optimal glycerol concentration balancing cryoprotection and potential interference with activity

• Oxidation prevention:

  • Include reducing agents appropriate for the specific activity (DTT, β-mercaptoethanol, TCEP)

  • Consider oxygen-free storage under nitrogen or argon for particularly oxidation-sensitive activities

  • Add antioxidants such as EDTA to chelate metal ions that catalyze oxidation reactions

• Activity monitoring protocol:

  • Establish a standardized activity assay suitable for routine quality control

  • Implement time-course stability studies at different temperatures

  • Create reference standards with known activity for comparative analysis

• Lyophilization assessment:

  • For long-term storage needs, evaluate activity retention after lyophilization with appropriate excipients

  • Compare activity recovery between lyophilized samples and those stored in solution

Documenting activity levels at regular intervals creates valuable stability profiles that inform optimal storage duration and conditions for maintaining SaurJH1_1665 functionality in research applications.

What strategies address issues with protein misfolding?

Addressing misfolding of SaurJH1_1665, particularly challenging due to its predicted membrane domains , requires both preventive and corrective approaches:

• Expression-phase strategies:

  • Reduce expression temperature to 16-20°C to slow translation and folding rates

  • Implement step-down induction protocols (initial growth at 37°C, induction and expression at lower temperatures)

  • Co-express with molecular chaperones (GroEL/GroES, DnaK/DnaJ/GrpE systems)

  • Test the impact of osmolytes (betaine, sorbitol) in the growth medium

• Solubilization approaches for inclusion bodies:

  • If SaurJH1_1665 forms inclusion bodies, develop mild solubilization protocols

  • Test graded concentrations of chaotropes (urea, guanidinium chloride)

  • Evaluate detergent-based solubilization (sarkosyl, SDS with subsequent detergent exchange)

  • Investigate pH-induced solubilization in extreme pH conditions followed by neutral pH refolding

• Refolding optimization:

  • Implement dialysis-based step-wise refolding to gradually remove denaturants

  • Test on-column refolding during affinity purification

  • Screen additives that promote folding (arginine, glutamine, glycerol, non-detergent sulfobetaines)

  • For membrane proteins, incorporate compatible detergents or lipids during refolding

• Structural analysis of folding status:

  • Use circular dichroism spectroscopy to assess secondary structure

  • Apply limited proteolysis to determine compact folded domains

  • Employ fluorescence spectroscopy to monitor tertiary structure

  • Consider differential scanning calorimetry to measure thermal stability

• Construct engineering:

  • Design truncation constructs removing problematic domains while retaining functional units

  • Create soluble domain constructs for functional characterization

  • Test fusion to highly soluble partners (MBP, SUMO, thioredoxin)

These approaches should be implemented in a systematic manner, with careful documentation of conditions that improve folding outcomes for SaurJH1_1665.

How can the specificity of antibodies against SaurJH1_1665 be verified?

Verifying antibody specificity for SaurJH1_1665 is crucial for reliable research outcomes. A comprehensive validation strategy includes:

• Positive and negative control testing:

  • Positive: Purified recombinant SaurJH1_1665 protein

  • Negative: Lysates from S. aureus strains with SaurJH1_1665 gene deletion

  • Specificity: Lysates from related Staphylococcus species expressing homologous proteins

• Cross-reactivity assessment:

  • Western blot analysis against whole cell lysates from multiple S. aureus strains

  • Testing against purified homologs (e.g., SAHV_1560) to evaluate cross-reactivity

  • Competition assays with purified protein to confirm signal displacement

• Epitope mapping:

  • Identify the specific regions recognized using peptide arrays

  • Test reactivity against truncated versions of SaurJH1_1665

  • Confirm accessibility of epitopes in native protein conformation

• Methodological validation:

  • Verify consistent results across multiple techniques (Western blot, immunoprecipitation, immunofluorescence)

  • Confirm expected subcellular localization pattern matches bioinformatic predictions

  • Test antibody performance under various fixation and sample preparation conditions

• Statistical validation:

  • Implement a pretest-posttest control group design comparing antibody performance before and after affinity purification

  • Conduct quantitative analysis of signal-to-noise ratios across different antibody concentrations

  • Perform replicate testing to ensure reproducibility of specificity results

Documentation should include all validation experiments with appropriate positive and negative controls, providing quantitative measures of specificity such as signal-to-noise ratios and cross-reactivity percentages with homologous proteins.