Recombinant Staphylococcus aureus UPF0344 protein USA300HOU_0928 (USA300HOU_0928)

How should researchers approach initial characterization of USA300HOU_0928?

Initial characterization should follow a systematic approach starting with bioinformatic analysis and progressing to experimental validation:

• Bioinformatic analysis: Conduct sequence homology searches to identify related proteins across bacterial species. Use topology prediction algorithms to estimate transmembrane regions and orientation.

• Expression testing: Evaluate expression in multiple systems, with E. coli being a proven viable host as demonstrated by successful commercial production . Test various expression conditions including temperature, induction timing, and media composition.

• Purification optimization: Implement a purification strategy including immobilized metal affinity chromatography (IMAC) utilizing the His-tag fusion, followed by size exclusion chromatography to achieve >90% purity as verified by SDS-PAGE .

• Structural validation: Employ circular dichroism spectroscopy to confirm proper folding and secondary structure content, particularly the alpha-helical content expected in a transmembrane protein.

• Localization studies: Perform subcellular fractionation and membrane extraction studies to confirm membrane association in both recombinant systems and native S. aureus.

This methodical approach establishes fundamental properties before proceeding to more complex functional studies.

What computational tools are most appropriate for predicting USA300HOU_0928 function?

For uncharacterized proteins like USA300HOU_0928, multiple computational approaches should be combined:

• Sequence-based tools: Beyond basic BLAST searches, employ position-specific scoring matrices and hidden Markov models to detect distant relationships with characterized proteins. These methods might identify subtle sequence patterns associated with specific functions.

• Structural prediction: Use AlphaFold2 or RoseTTAFold to generate structural models, then compare these models against structural databases to identify potential functional homologs even when sequence similarity is low.

• Genomic context analysis: Examine the genomic neighborhood of USA300HOU_0928 across Staphylococcus species. Genes consistently co-located with USA300HOU_0928 may have related functions, providing clues to its role.

• Gene expression correlation networks: Analyze transcriptomic data to identify genes whose expression patterns correlate with USA300HOU_0928 across different conditions, suggesting functional relationships.

• Protein-protein interaction prediction: Use tools that predict potential interaction partners based on sequence features, co-evolution patterns, or structural compatibility.

While these computational approaches generate hypotheses rather than definitive answers, they guide subsequent experimental design by narrowing the functional possibilities to test.

What expression systems yield optimal results for recombinant USA300HOU_0928?

Expression of membrane proteins like USA300HOU_0928 presents unique challenges requiring specialized approaches:

• E. coli expression system: Successfully employed for commercial production of USA300HOU_0928 as documented in search result . When using E. coli, consider:

  • Strain selection: BL21(DE3) serves as a standard strain, but C41(DE3) and C43(DE3) are specifically engineered for membrane protein expression with reduced toxicity .

  • Vector design: Vectors with tightly regulated promoters prevent leaky expression that may be toxic.

  • Fusion partners: The His-SUMO tag fusion strategy enhances both purification and solubility .

• Alternative expression systems:

  • Cell-free systems: Allow direct incorporation into detergent micelles during synthesis.

  • Yeast expression: Provides a eukaryotic membrane environment that may improve folding.

  • Insect cell expression: Offers complex post-translational modifications if required.

Experimental data confirms that E. coli expression with His-tagging produces functional USA300HOU_0928 with purity exceeding 90% as determined by SDS-PAGE , making this the recommended starting approach for most research applications.

What purification strategy maximizes yield and purity of USA300HOU_0928?

A multi-step purification strategy optimized for membrane proteins yields the best results:

• Cell lysis and membrane preparation:

  • Mechanical disruption (sonication or high-pressure homogenization) in buffer containing protease inhibitors

  • Separation of membrane fraction by ultracentrifugation

  • Membrane solubilization using appropriate detergents (typically mild non-ionic detergents like DDM or LDAO)

• Affinity chromatography:

  • IMAC using Ni-NTA resin to capture the His-tagged protein

  • Optimized imidazole gradient to minimize non-specific binding while maximizing target protein elution

  • Sample analysis by SDS-PAGE to identify target protein-containing fractions

• Size exclusion chromatography:

  • Secondary purification step to separate monomeric protein from aggregates

  • Buffer containing detergent at concentrations above critical micelle concentration

  • Collection of fractions corresponding to properly folded protein

• Quality assessment:

  • SDS-PAGE to confirm >90% purity as specified in the product information

  • Western blotting with anti-His antibodies for identity confirmation

  • Mass spectrometry for molecular weight verification

This strategy consistently produces high-purity protein suitable for structural and functional studies.

How can researchers troubleshoot common issues in USA300HOU_0928 expression?

When encountering problems with USA300HOU_0928 expression, systematic troubleshooting should address:

• Low expression yield:

  • Problem: Minimal protein production despite confirmed plasmid integrity

  • Solution: Lower induction temperature (16-20°C), reduce IPTG concentration, optimize induction timing (mid-log phase), and extend expression time (16-24 hours)

  • Measurement: Quantify improvement using Western blot analysis of whole-cell lysates

• Inclusion body formation:

  • Problem: Protein forms insoluble aggregates rather than integrating into membranes

  • Solution: Use solubility-enhancing fusion partners like SUMO , lower expression temperature, or co-express with molecular chaperones

  • Verification: Compare soluble versus insoluble fractions by Western blotting

• Host cell toxicity:

  • Problem: Growth inhibition or cell death following induction

  • Solution: Use specialized strains like C41(DE3) designed for toxic protein expression , implement tighter promoter control, or reduce expression level

  • Monitoring: Track growth curves post-induction to quantify improvement

• Poor detergent extraction:

  • Problem: Low recovery during membrane solubilization

  • Solution: Screen multiple detergent types and concentrations, optimize detergent:protein ratio, adjust salt concentration

  • Analysis: Quantify protein in solubilized versus insoluble fractions after detergent treatment

Addressing these common challenges through systematic parameter optimization significantly improves USA300HOU_0928 production outcomes.

What experimental approaches can determine the membrane topology of USA300HOU_0928?

Determining membrane protein topology requires complementary experimental strategies:

• Cysteine accessibility methods:

  • Methodology: Introduce single cysteine residues at predicted loop regions and test their accessibility to membrane-impermeable sulfhydryl reagents

  • Implementation: Generate a series of single-cysteine mutants (native sequence contains no cysteines), express in E. coli, and probe with PEG-maleimide

  • Data analysis: Accessible cysteines show mobility shifts on SDS-PAGE, revealing their membrane orientation

• Reporter fusion strategy:

  • Methodology: Create truncations at different positions fused to reporters like alkaline phosphatase (active in periplasm) or GFP (fluorescent in cytoplasm)

  • Implementation: Generate 8-10 fusion constructs targeting predicted loops, express in E. coli, and measure reporter activity

  • Interpretation: Activity patterns reveal which segments face cytoplasm versus periplasm

• Protease protection assays:

  • Methodology: Expose membrane vesicles containing the protein to proteases, then identify protected fragments

  • Implementation: Express USA300HOU_0928 in E. coli, prepare inside-out and right-side-out membrane vesicles, treat with proteases, and analyze by Western blotting

  • Analysis: Fragments protected in one orientation but digested in the other reveal topology

• Epitope mapping:

  • Methodology: Insert epitope tags at various positions and test accessibility using antibodies

  • Implementation: Create multiple constructs with small epitopes (FLAG, HA) at predicted loops, express in cells, and perform immunofluorescence with and without membrane permeabilization

  • Data interpretation: Epitopes accessible without permeabilization are extracellular

Combining data from multiple approaches produces a reliable topology model that guides further functional studies.

What functional assays can help elucidate the biological role of USA300HOU_0928?

For proteins of unknown function like USA300HOU_0928, a multi-faceted approach to functional characterization is essential:

• Genetic manipulation in S. aureus:

  • Gene deletion: Create knockout mutants and assess phenotypic changes in growth, stress resistance, virulence, and antibiotic susceptibility

  • Complementation: Re-introduce wild-type or mutant versions to confirm phenotype specificity

  • Overexpression: Analyze effects of elevated protein levels on cellular physiology

• Protein interaction studies:

  • Pull-down assays: Use purified His-tagged USA300HOU_0928 to identify binding partners from S. aureus lysates

  • Bacterial two-hybrid: Screen for interacting proteins in a library format

  • Crosslinking experiments: Capture transient interactions within the membrane environment

• Transport function assessment:

  • Liposome reconstitution: Incorporate purified protein into liposomes with fluorescent indicators

  • Substrate screening: Test transport of ions, metabolites, or antibiotics

  • Electrophysiology: Assess channel activity using patch-clamp techniques

• Structural changes under varying conditions:

  • pH sensitivity: Monitor structural changes across physiological pH range

  • Ligand binding: Screen potential ligands using thermal shift assays

  • Metal binding: Assess interactions with divalent cations common in bacterial physiology

This systematic approach progressively narrows potential functions while generating testable hypotheses about USA300HOU_0928's biological role.

How can site-directed mutagenesis inform USA300HOU_0928 function?

Site-directed mutagenesis provides critical insights into structure-function relationships:

For USA300HOU_0928, an initial panel of 8-10 strategically selected mutations can provide significant functional insights when systematically characterized through this approach.

What structural characterization methods are most suitable for USA300HOU_0928?

Membrane proteins like USA300HOU_0928 require specialized structural approaches:

• Preliminary structural assessment:

  • Circular dichroism (CD) spectroscopy: Quantifies secondary structure content, particularly alpha-helical components expected in transmembrane domains

  • Size exclusion chromatography with multi-angle light scattering (SEC-MALS): Determines oligomeric state in detergent solution

  • Differential scanning calorimetry (DSC): Measures thermal stability and identifies buffer conditions for structural studies

• High-resolution structural methods:

  • X-ray crystallography: Requires extensive crystallization screening with specific membrane protein techniques, including lipidic cubic phase crystallization

  • Cryo-electron microscopy: Increasingly successful for smaller membrane proteins when incorporated into nanodiscs or amphipols

  • NMR spectroscopy: Viable for smaller membrane proteins like USA300HOU_0928 when isotopically labeled

• Computational structural analysis:

  • Homology modeling: Construct models based on related structures if available

  • Ab initio prediction: Use algorithms like AlphaFold2 specifically parameterized for membrane proteins

  • Molecular dynamics simulations: Simulate behavior in membrane environments

• Hybrid approach implementation:

  • Initial characterization using spectroscopic methods

  • Information on protein dynamics from hydrogen-deuterium exchange mass spectrometry

  • Integration of low-resolution experimental data with computational models

For USA300HOU_0928, a strategic pipeline beginning with CD spectroscopy and progressing to either solution NMR or cryo-EM offers the most promising path to structural insights.

How can researchers prepare USA300HOU_0928 samples for structural studies?

Sample preparation critically impacts structural analysis success:

• Expression optimization for structural studies:

  • Isotopic labeling: For NMR studies, establish protocols for 15N, 13C, and 2H labeling in E. coli minimal media

  • Selenomethionine incorporation: For X-ray crystallography phasing, if pursuing crystallographic approaches

  • Scale-up considerations: Develop strategies for producing milligram quantities of pure protein

• Detergent and lipid screening:

  • Systematic detergent testing: Screen detergent panel (DDM, LMNG, LDAO, etc.) for optimal protein stability

  • Detergent exchange methods: Implement on-column detergent exchange during purification

  • Reconstitution approaches: Test incorporation into nanodiscs, liposomes, or amphipols

• Sample homogeneity optimization:

  • Size exclusion chromatography: Final polishing step to ensure monodisperse samples

  • Dynamic light scattering: Verify sample monodispersity before structural experiments

  • Negative-stain electron microscopy: Preliminary assessment of sample quality

• Stability enhancement:

  • Ligand addition: Include potential stabilizing ligands if identified

  • Buffer optimization: Conduct thermal shift assays to identify stabilizing buffer components

  • Construct engineering: Consider thermostabilizing mutations or fusion partners

Following product specifications in search result , reconstituting lyophilized protein in deionized sterile water (0.1-1.0 mg/mL) with appropriate detergent and stability enhancers provides a starting point for structural sample preparation.

What computational approaches complement experimental structural studies of USA300HOU_0928?

Computational methods significantly enhance structural analysis:

• Sequence-based structure prediction:

  • Transmembrane topology prediction: Use specialized algorithms (TMHMM, TOPCONS) to identify membrane-spanning regions

  • Secondary structure prediction: Predict alpha-helical content and orientation

  • Coevolution analysis: Identify potentially interacting residues through evolutionary coupling analysis

• Advanced structural modeling:

  • Template-based modeling: Use structures of related membrane proteins as templates

  • Deep learning approaches: Apply AlphaFold2 or similar tools optimized for membrane proteins

  • Integrative modeling: Combine low-resolution experimental data with computational predictions

• Molecular dynamics simulations:

  • Membrane embedding: Simulate USA300HOU_0928 in realistic lipid bilayers

  • Stability assessment: Evaluate structural stability during extended simulations

  • Potential binding site identification: Probe surface for potential ligand binding pockets

• Virtual screening applications:

  • Binding site prediction: Identify potential functional sites on the protein surface

  • Ligand docking: Screen compound libraries against predicted binding sites

  • Protein-protein interaction modeling: Predict potential interaction partners

For USA300HOU_0928, a hierarchical approach beginning with topology prediction, followed by AlphaFold2 modeling and membrane-embedded molecular dynamics simulations provides a solid computational foundation to guide and interpret experimental studies.

How might USA300HOU_0928 contribute to S. aureus pathogenicity?

Understanding USA300HOU_0928's potential role in pathogenicity requires exploration of several mechanisms:

• Virulence phenotype assessment:

  • Infection models: Compare wild-type to USA300HOU_0928 knockout strains in cell culture invasion assays and animal infection models

  • Biofilm formation: Evaluate contributions to biofilm development and architecture

  • Host cell interactions: Assess effects on adhesion to and invasion of host cells

• Stress response functions:

  • Antimicrobial peptide resistance: Test sensitivity to host defensive peptides

  • pH adaptation: Evaluate growth and survival under varying pH conditions mimicking host environments

  • Oxidative stress handling: Measure resistance to reactive oxygen species produced during immune response

• Potential virulence regulation:

  • Expression analysis: Monitor USA300HOU_0928 expression during different infection stages

  • Regulatory interactions: Identify whether USA300HOU_0928 affects expression of established virulence factors

  • Signal transduction: Investigate potential role in sensing host environment cues

S. aureus is known to cause various infections ranging from minor skin infections to life-threatening conditions through virulence factors and surface proteins . USA300HOU_0928's membrane localization suggests potential roles in host-pathogen interactions or environmental adaptation mechanisms relevant to pathogenicity.

What is the potential of USA300HOU_0928 as an antimicrobial target?

Evaluating USA300HOU_0928 as a potential therapeutic target requires systematic assessment:

• Target validation criteria:

  • Essentiality: Determine whether USA300HOU_0928 is essential for bacterial growth or virulence

  • Conservation: Analyze presence and sequence conservation across clinical S. aureus isolates

  • Human homology: Confirm absence of close human homologs to minimize off-target effects

• Druggability assessment:

  • Structural analysis: Identify potential binding pockets suitable for small molecule binding

  • Surface accessibility: Evaluate whether key functional regions are accessible to inhibitors

  • Assay development: Establish functional assays suitable for screening inhibitor candidates

• Therapeutic strategy development:

  • Inhibition approaches: Design strategies to block protein function through small molecules

  • Antibody-based approaches: Explore potential for antibody targeting if external epitopes are identified

  • Combination approaches: Assess synergy with existing antibiotics

• Resistance development risk:

  • Mutation rate analysis: Assess natural variation in clinical isolates

  • Resistance mechanism prediction: Evaluate potential bypass mechanisms

  • Evolutionary pressure analysis: Consider selective pressures on target conservation

While specific information on USA300HOU_0928 as an antimicrobial target is not directly provided in the search results, its presence in methicillin-resistant S. aureus strains highlights potential relevance to addressing antibiotic resistance challenges.

How can recombinant USA300HOU_0928 be utilized in vaccine development research?

Recombinant USA300HOU_0928 offers several applications in vaccine research:

• Antigen evaluation:

  • Immunogenicity assessment: Test purified recombinant protein for antibody response in animal models

  • Epitope mapping: Identify immunodominant regions using peptide arrays and deletion constructs

  • Protective capacity: Evaluate whether antibodies against USA300HOU_0928 provide protection in challenge models

• Vaccine formulation approaches:

  • Subunit vaccine components: Test recombinant full-length protein or selected domains

  • Peptide-based vaccines: Design peptides based on immunogenic epitopes

  • Adjuvant combinations: Optimize formulations for enhanced immune response

• Cross-protection potential:

  • Sequence conservation analysis: Compare USA300HOU_0928 sequences across S. aureus strains

  • Cross-reactivity testing: Assess whether antibodies recognize protein from diverse clinical isolates

  • Strain coverage prediction: Estimate potential protection breadth based on epitope conservation

• Immune response characterization:

  • Antibody isotype analysis: Determine IgG subclasses elicited by immunization

  • T-cell response assessment: Characterize cellular immunity components

  • Memory response evaluation: Measure duration of protective immunity

The recombinant protein described in search result with >90% purity provides suitable material for initial immunogenicity testing, though it should be noted that products from Creative BioMart specify they are for research purposes only and cannot be used directly on humans or animals .

How should researchers store and handle recombinant USA300HOU_0928 to maintain activity?

Proper storage and handling are essential for maintaining protein integrity:

• Storage recommendations:

  • Long-term storage: Store lyophilized powder or aliquoted protein at -20°C/-80°C as recommended in search result

  • Aliquoting strategy: Prepare single-use aliquots to avoid repeated freeze-thaw cycles, which are specifically noted to be detrimental

  • Storage buffer: Use Tris/PBS-based buffer with 6% Trehalose at pH 8.0 as specified in the product information

• Reconstitution protocol:

  • Initial preparation: Briefly centrifuge vial before opening to bring contents to the bottom

  • Reconstitution medium: Use deionized sterile water to achieve concentration of 0.1-1.0 mg/mL

  • Stabilizer addition: Add glycerol to 5-50% final concentration for freezing, with 50% being the recommended default

• Working solution handling:

  • Short-term storage: Store working aliquots at 4°C for up to one week

  • Temperature sensitivity: Keep on ice during experiments

  • Concentration considerations: Avoid excessive dilution which may promote adsorption to containers

• Quality verification:

  • Activity monitoring: Establish functional assays to verify retained activity

  • Physical appearance: Monitor for visible aggregation or precipitation

  • Periodic testing: Implement quality control testing for long-term stored material

Following these specific guidelines from search result helps ensure experimental reproducibility and maximal protein activity.

What controls should be included in USA300HOU_0928 functional studies?

Rigorous experimental design requires appropriate controls:

• Negative controls:

  • Heat-denatured protein: Verify that observed effects require properly folded protein

  • Buffer-only controls: Account for buffer component effects

  • Unrelated membrane protein: Distinguish specific effects from general membrane protein properties

• Positive controls:

  • Known functional domains: If functional motifs are identified, use proteins with established similar activities

  • Related proteins: Test characterized members of the UPF0344 family if available

  • Activity standards: Include calibrated standards for quantitative assays

• Expression system controls:

  • Empty vector transformants: Control for host cell background effects

  • Tag-only constructs: Account for effects of fusion tags

  • Endotoxin testing: Verify absence of contaminating bacterial components

• Genetic manipulation controls:

  • Complemented knockout strains: Confirm phenotype restoration with wild-type gene

  • Point mutant series: Include both function-disrupting and function-preserving mutations

  • Overexpression toxicity controls: Verify phenotypes aren't due to protein burden

These controls ensure that observed effects can be confidently attributed to USA300HOU_0928 function rather than experimental artifacts.

What are the key considerations for designing reproducible experiments with USA300HOU_0928?

Ensuring experimental reproducibility requires attention to multiple factors:

• Protein batch consistency:

  • Production standardization: Establish consistent expression and purification protocols

  • Quality control metrics: Define acceptance criteria for purity (>90% by SDS-PAGE) , yield, and activity

  • Batch comparison: Validate new batches against reference standards before use

• Experimental condition standardization:

  • Buffer composition: Maintain consistent pH, ionic strength, and additive concentrations

  • Temperature control: Conduct experiments at defined, controlled temperatures

  • Timing considerations: Standardize incubation times and measurement intervals

• Quantification methodologies:

  • Protein concentration determination: Use multiple methods (Bradford, BCA, A280) for verification

  • Activity normalization: Normalize results to protein amount or specific activity

  • Statistical approaches: Implement appropriate statistical tests with adequate replication

• Documentation and reporting:

  • Detailed methods: Document all experimental parameters including reagent sources and lot numbers

  • Raw data preservation: Maintain complete datasets including controls and replicates

  • Reagent sharing: Consider depositing plasmids in public repositories for community access

These practices ensure that results with USA300HOU_0928 can be reproduced both within the same laboratory and by independent researchers, advancing collective understanding of this uncharacterized S. aureus protein.