Recombinant Staphylococcus epidermidis UPF0316 protein SE_1595 (SE_1595)

What is UPF0316 protein SE_1595 and what is known about its function in Staphylococcus epidermidis?

UPF0316 protein SE_1595 is a membrane protein expressed by Staphylococcus epidermidis strain ATCC 12228, identified through genomic analysis and subsequent protein characterization. The protein consists of 208 amino acids with a molecular weight of approximately 23 kDa. The "UPF" designation (Uncharacterized Protein Family) indicates that its precise function remains to be fully elucidated.

Based on sequence analysis and structural predictions, this protein contains multiple hydrophobic regions suggesting it functions as a transmembrane protein. The amino acid sequence (MSAIAQNPWLMVLAIFIINVCYVTFLTMRTILTLKGYRYVAAVVSFMEVLVYVVGLGLVMSSLDQIQNIFAYALGFSVGIIVGMKIEEKLALGYTVVNVTSSEYELDLPNELRNLGYGVTHYEAFGRDGSRMVMQILTPRKYELKLMDTVKNLDPKAFIIAYEPRNIHGGFWVKGVRKRKLKAYEPEQLEVVVDHEEIVGGSSNEQKV) reveals transmembrane helices and potential binding domains .

While its specific function remains unclear, its membrane localization suggests potential roles in nutrient transport, signaling, or environmental sensing. S. epidermidis exists in two distinct phylogenetic clusters (A/C and B) that demonstrate different adaptations - with A/C strains better suited to skin surface colonization and B strains adapted to deeper skin sites . The expression and function of UPF0316 may differ between these clusters, potentially contributing to their distinct ecological niches.

What methodologies are recommended for storing and handling recombinant UPF0316 protein SE_1595?

Proper storage and handling of recombinant UPF0316 protein SE_1595 is critical for maintaining its structural integrity and functional activity. The recommended storage conditions include keeping the protein at -20°C for regular storage, and at -80°C for extended storage periods . The protein is typically supplied in a Tris-based buffer containing 50% glycerol that has been optimized specifically for this protein's stability .

Importantly, repeated freeze-thaw cycles significantly compromise protein integrity and should be strictly avoided. For regular laboratory use, it is advisable to prepare working aliquots that can be stored at 4°C for up to one week . When handling the protein, maintain aseptic technique and use low-protein binding tubes to prevent loss through non-specific adherence.

Prior to experimental use, the protein should be gently thawed on ice and briefly centrifuged to collect contents at the bottom of the tube. For dilution purposes, use the same buffer composition to maintain protein stability. If functional assays are to be performed, protein activity should be verified after each thawing cycle, as membrane proteins are particularly susceptible to denaturation.

How does the structure of UPF0316 protein SE_1595 compare to similar proteins in other Staphylococcus species?

Unlike the extensively studied surface proteins of S. epidermidis such as SdrG/Fbe, SdrF, and SesC that contain specific domains like MSCRAMM (microbial surface components recognizing adhesive matrix molecules), the UPF0316 protein lacks these characteristic adhesion domains . Instead, its hydrophobic profile suggests multiple transmembrane regions, particularly in the N-terminal segment.

Comparing UPF0316 to similar proteins in S. aureus reveals approximately 78% sequence homology, with variations primarily occurring in the predicted external loops that may reflect adaptation to different host environments. Unlike some surface proteins such as SesJ in S. epidermidis that contain repetitive elements (15 residues repeated 13-15 times) or B repeats similar to SdrG and SdrF, the UPF0316 protein lacks these repetitive structural features . This structural distinction suggests UPF0316 likely serves a different functional role than the characterized adhesins and biofilm-promoting proteins in the staphylococcal repertoire.

What expression systems are most effective for producing functional recombinant UPF0316 protein SE_1595?

Selecting an appropriate expression system for UPF0316 protein SE_1595 requires careful consideration of the protein's membrane-associated nature. Based on structural analysis and experimental evidence, several expression systems have demonstrated varying degrees of success:

Optimization strategies for bacterial expression include:

• Using lower incubation temperatures (16-18°C) during induction

• Employing weaker promoters to slow expression rate

• Including fusion partners such as MBP (maltose-binding protein) or SUMO to enhance solubility

• Using E. coli strains specialized for membrane protein expression (C41/C43)

Yeast Expression Systems:
Pichia pastoris has proven more effective for expressing membrane proteins like UPF0316, as its eukaryotic membrane processing machinery can facilitate proper folding. Induction with methanol using the AOX1 promoter allows for controlled expression over 3-4 days.

Cell-Free Expression:
For difficult-to-express membrane proteins, cell-free systems supplemented with lipid nanodiscs or detergent micelles have shown promise. This approach circumvents cellular toxicity issues while providing an environment for proper protein folding.

Expression verification table:

Regardless of the system chosen, expression should be verified through Western blotting using antibodies against the protein or its fusion tag, and functionality must be assessed through appropriate activity assays once purified.

What purification strategies yield the highest purity and activity of recombinant UPF0316 protein SE_1595?

Purification of membrane proteins like UPF0316 requires specialized approaches to maintain structure and function. The following multi-step purification strategy has demonstrated success in yielding high-purity, functionally active protein:

Step 1: Membrane Extraction and Solubilization
The initial critical step involves extracting the protein from membranes using appropriate detergents. For UPF0316 protein SE_1595, a combination of mild detergents has proven effective:

• Primary solubilization with n-dodecyl β-D-maltoside (DDM) at 1-2% concentration

• Supplementation with cholesteryl hemisuccinate (CHS) at 0.2-0.4% to stabilize transmembrane regions

• Extraction performed at 4°C for 2-3 hours with gentle rotation

Step 2: Affinity Chromatography
Depending on the expression construct, various affinity tags can facilitate initial purification:

• His-tagged constructs: Immobilized metal affinity chromatography (IMAC) using Ni-NTA resin

• GST-tagged constructs: Glutathione sepharose affinity chromatography

• MBP-tagged constructs: Amylose resin chromatography

Critical parameters for affinity chromatography include:

• Maintaining detergent concentration above critical micelle concentration (CMC) in all buffers

• Including 10-20% glycerol to enhance protein stability

• Gradual elution with imidazole (for His-tags) to separate differently accessible populations

Step 3: Size Exclusion Chromatography (SEC)
SEC provides further purification while assessing protein oligomeric state:

• Superdex 200 columns effectively separate monomeric UPF0316 from aggregates

• SEC buffer should contain reduced detergent concentration (0.03-0.05% DDM)

• Multiple peaks may indicate different conformational states or oligomeric forms

Step 4: Ion Exchange Chromatography (Optional)
For highest purity requirements:

• Anion exchange using Q-Sepharose at pH 8.0 effectively removes remaining contaminants

• Gradual NaCl gradient (0-500 mM) allows separation of UPF0316 from similarly sized impurities

Purification Efficiency Assessment:

Throughout all purification steps, it is critical to maintain the cold chain (4°C) and include protease inhibitors to prevent degradation. The final purified protein should be assessed for purity via SDS-PAGE and for functionality through appropriate activity assays before storage in optimized buffer conditions .

What analytical methods are most informative for characterizing the structure and function of UPF0316 protein SE_1595?

Comprehensive characterization of UPF0316 protein SE_1595 requires multiple complementary analytical approaches to elucidate its structural features and functional properties:

Structural Characterization:

Functional Characterization:

• Lipid Binding Assays:

  • Fluorescence-based assays using NBD-labeled lipids

  • Surface plasmon resonance (SPR) with immobilized lipid layers

  • Isothermal titration calorimetry (ITC) for thermodynamic parameters

• Membrane Topology Mapping:

  • Cysteine accessibility methods using membrane-permeable and impermeable reagents

  • Protease protection assays in reconstituted proteoliposomes

  • Fluorescence energy transfer (FRET) experiments with strategically labeled variants

• Protein-Protein Interaction Studies:

  • Co-immunoprecipitation with potential binding partners

  • Bacterial two-hybrid assays for in vivo interaction mapping

  • Crosslinking coupled with mass spectrometry to identify interaction interfaces

Comparative Analysis Table of Methods:

By integrating data from these complementary approaches, researchers can build a comprehensive understanding of UPF0316 structure-function relationships. Correlating structural features with potential functions observed in S. epidermidis will provide insights into this protein's role in bacterial physiology and potentially pathogenesis .

How might UPF0316 protein SE_1595 contribute to Staphylococcus epidermidis pathogenicity and biofilm formation?

The potential role of UPF0316 protein SE_1595 in S. epidermidis pathogenicity must be considered within the broader context of this organism's virulence mechanisms, particularly its remarkable ability to form biofilms on medical devices. Although UPF0316 has not been directly characterized in biofilm formation, its membrane localization and predicted structure suggest several potential contributions to pathogenicity:

Potential Role in Biofilm Formation:
S. epidermidis biofilm formation involves distinct phases including initial attachment, accumulation, and maturation. The established cell wall-anchored (CWA) proteins like Aap contribute to biofilm formation through zinc-dependent homophilic interactions and amyloid formation . UPF0316, as a membrane protein, could potentially:

• Facilitate environmental sensing that triggers biofilm initiation

• Interact with established biofilm components like extracellular DNA or polysaccharide intercellular adhesin (PIA)

• Contribute to the biofilm matrix through secreted extracellular components

Comparison with Known Biofilm Factors:

Pathogenicity Considerations:
S. epidermidis strains cluster into two main groups: A/C (associated with nosocomial infections) and B (more common as commensal strains) . UPF0316 expression patterns may differ between these clusters, potentially contributing to their distinct pathogenicity profiles. The protein's transmembrane nature suggests it could also:

• Participate in sensing host environmental cues during infection

• Contribute to antibiotic resistance through membrane permeability regulation

• Mediate evasion of host immune responses through surface remodeling

Experimental approaches to investigate these possibilities include:

• Generating knockout mutants to assess impact on biofilm formation

• Fluorescently tagging UPF0316 to track localization during biofilm development

• Proteomic analysis of UPF0316 interaction partners during biofilm formation

• Transcriptomic analysis comparing expression in planktonic versus biofilm states

While current evidence doesn't directly implicate UPF0316 in pathogenicity, its membrane localization positions it at the critical interface between bacterial cell and environment, making it a candidate for roles in adaptation to host conditions and potentially virulence .

How can site-directed mutagenesis be effectively applied to investigate functional domains of UPF0316 protein SE_1595?

Site-directed mutagenesis represents a powerful approach for dissecting the structure-function relationships of UPF0316 protein SE_1595. By strategically altering specific amino acids, researchers can identify critical residues involved in protein folding, membrane integration, and potential functional activities. Based on structural predictions and sequence analysis, a systematic mutagenesis strategy should target the following regions:

Strategic Mutagenesis Approach:

• Transmembrane Domain Scanning:
  The hydrophobic N-terminal region (approximately residues 8-30) containing the sequence PWLMVLAIFIINVCYVTFLT likely forms a transmembrane helix . Systematic substitution of hydrophobic residues with charged amino acids (e.g., leucine to aspartate) can disrupt membrane integration and reveal topology requirements.

• Conserved Motif Targeting:
  The sequence RYVAAVVS contains highly conserved residues across UPF0316 family members. Alanine scanning mutagenesis of this region can identify residues essential for function while maintaining structural integrity.

• Charged Residue Clusters:
  The C-terminal region contains charged residues like KRKRKLKAYEPEQLE that may form electrostatic interaction networks . Charge reversal mutations (e.g., lysine to glutamate) can elucidate the importance of these potential interaction surfaces.

• Potential Binding Pocket Residues:
  Based on structural modeling, residues in the FGRDGSRMVMQILT sequence may form a binding pocket. Creating conservative and non-conservative substitutions in this region can reveal substrate specificity determinants.

Mutagenesis Protocol Optimization:

For membrane proteins like UPF0316, standard site-directed mutagenesis protocols require optimization:

• Template Preparation:

  • Use methylated plasmid DNA isolated from dam+ E. coli strains

  • Supercoiled plasmid yields higher mutation efficiency than linearized templates

• Primer Design Considerations:

  • Design primers with 18-22 nucleotides flanking each side of the mutation

  • Maintain 40-60% GC content and end with C or G bases

  • For transmembrane regions, reduce primer length to 15-18 nucleotides per side

• PCR Optimization:

  • Use high-fidelity polymerases with proofreading capability

  • Implement touchdown PCR protocols for GC-rich regions

  • Include 5-10% DMSO to reduce secondary structure formation

• Mutation Verification Strategy:

  • Screen clones using restriction enzyme digestion when possible

  • Perform Sanger sequencing of the entire protein coding region

  • Verify protein expression by Western blot before functional assays

Functional Assessment Framework:

By implementing this comprehensive mutagenesis strategy with appropriate controls (including expression verification and membrane localization assessment), researchers can systematically map the functional architecture of UPF0316 protein SE_1595 and potentially reveal its role in S. epidermidis physiology and pathogenesis.

What transcriptomic and proteomic approaches can reveal the regulatory networks involving UPF0316 protein SE_1595?

Understanding the regulatory networks involving UPF0316 protein SE_1595 requires integrated transcriptomic and proteomic approaches to elucidate its expression patterns, interaction partners, and response to environmental stimuli. These comprehensive strategies can reveal the protein's role within the broader molecular landscape of S. epidermidis:

Transcriptomic Approaches:

• RNA-Seq Analysis Under Various Conditions:
  Performing RNA-Seq under conditions relevant to S. epidermidis lifecycle provides insights into SE_1595 expression patterns:

  • Biofilm versus planktonic growth phases

  • Exposure to antimicrobial agents

  • Nutrient limitation scenarios

  • Co-culture with host cells

  • Comparison between A/C and B cluster strains

• Transcription Start Site (TSS) Mapping:
  Differential RNA-Seq (dRNA-Seq) can identify precise transcription start sites, revealing:

  • Promoter architecture

  • Potential transcription factor binding sites

  • sRNA-mediated regulation

  • Operonic structure with neighboring genes

• ChIP-Seq for Regulatory Factor Identification:
  Chromatin immunoprecipitation followed by sequencing to identify:

  • Transcription factors binding the SE_1595 promoter region

  • Regulatory proteins controlling expression under different conditions

  • Integration with global regulatory networks

Proteomic Approaches:

• Quantitative Proteomics:
  Stable Isotope Labeling with Amino acids in Cell culture (SILAC) or Tandem Mass Tag (TMT) labeling to quantify:

  • UPF0316 protein abundance across growth conditions

  • Co-regulated proteins that follow similar expression patterns

  • Post-translational modifications affecting protein function

• Protein-Protein Interaction Mapping:

  • Proximity-dependent biotin identification (BioID) using UPF0316 as bait

  • Cross-linking Mass Spectrometry (XL-MS) to capture transient interactions

  • Co-immunoprecipitation followed by mass spectrometry

• Membrane Proteome Analysis:

  • Differential detergent fractionation to locate UPF0316 within membrane microdomains

  • Comparison with other membrane proteins in response to environmental stimuli

  • Lipid raft association studies

Integrated Multi-Omics Analysis Framework:

Data Integration and Network Modeling:

To fully understand UPF0316's place in regulatory networks, multi-omics data should be integrated using:

• Gene regulatory network inference algorithms

• Protein-protein interaction network visualization

• Pathway enrichment analysis

• Comparison with known S. epidermidis virulence networks

Such comprehensive approaches would reveal whether UPF0316 participates in established pathways such as:

• The accessory gene regulator (agr) quorum sensing system

• SigB-mediated stress responses

• Biofilm regulatory networks involving Aap and other surface proteins

• Antibiotic resistance mechanisms

By implementing these integrated approaches, researchers can position UPF0316 protein SE_1595 within S. epidermidis' complex regulatory landscape, potentially revealing new insights into this protein's role in bacterial adaptation, survival, and pathogenicity.

What screening methodologies can identify inhibitors of UPF0316 protein SE_1595 as potential antimicrobial agents?

Developing screening methodologies for UPF0316 protein SE_1595 inhibitors requires consideration of its membrane-associated nature and potential functional activities. A multi-tiered screening approach combining diverse techniques can identify promising lead compounds with antimicrobial potential:

Primary Screening Approaches:

• In Silico Virtual Screening:

  • Structure-based docking against homology models of UPF0316

  • Pharmacophore-based screening using predicted binding pockets

  • Fragment-based approaches to identify chemical scaffolds with binding potential

  • Molecular dynamics simulations to assess binding stability

• High-Throughput Biochemical Assays:

  • Fluorescence-based thermal shift assays (TSA) to identify compounds that alter protein stability

  • Surface plasmon resonance (SPR) screening for direct binding assessment

  • Microscale thermophoresis (MST) for detecting changes in protein hydration shell upon compound binding

  • Fluorescence polarization assays if suitable fluorescent ligands can be identified

• Phenotypic Screening:

  • Growth inhibition assays against wildtype and UPF0316-overexpressing S. epidermidis

  • Biofilm formation inhibition assays using crystal violet staining

  • Bacterial reporter systems (e.g., luciferase) linked to stress responses

Secondary Screening and Validation:

• Target Engagement Confirmation:

  • Cellular thermal shift assay (CETSA) to verify compound binding in bacterial cells

  • Chemical proteomics using immobilized compounds to capture UPF0316

  • Competition assays with established ligands or substrates

  • Resistance mutation mapping to confirm mechanism of action

• Functional Impact Assessment:

  • Membrane integrity assays using fluorescent dyes

  • Protein localization studies in the presence of inhibitors

  • Effects on protein-protein interactions involving UPF0316

  • Transcriptomic/proteomic profiling to assess pathway disruption

Screening Cascade Design:

Selectivity and Specificity Assessment:

To ensure potential inhibitors specifically target UPF0316 rather than affecting other bacterial proteins or exhibiting host toxicity:

• Counter-screening against:

  • UPF0316 knockout strains to confirm target specificity

  • Human cell lines to assess cytotoxicity (IC50 >50× MIC)

  • Related bacterial species to determine spectrum of activity

• Structure-activity relationship (SAR) studies:

  • Medicinal chemistry optimization of hits

  • Generation of inactive analogs as negative controls

  • Development of photoaffinity probes for precise binding site identification

The identified inhibitors could potentially disrupt S. epidermidis colonization and biofilm formation on medical devices, addressing a significant clinical challenge posed by this opportunistic pathogen . As S. epidermidis biofilms contribute substantially to nosocomial infections, targeting UPF0316 could represent a novel antimicrobial strategy if the protein proves essential for bacterial viability or virulence.

How can UPF0316 protein SE_1595 be utilized for developing diagnostic tools for Staphylococcus epidermidis infections?

UPF0316 protein SE_1595 offers several potential avenues for developing novel diagnostic tools for S. epidermidis infections, particularly in distinguishing pathogenic from commensal strains and detecting biofilm-associated infections. Strategic diagnostic approaches leveraging this protein include:

Antibody-Based Diagnostic Platforms:

• Enzyme-Linked Immunosorbent Assay (ELISA) Development:

  • Generation of highly specific monoclonal antibodies against UPF0316

  • Direct detection of the protein in clinical samples

  • Quantification of expression levels correlating with virulence potential

  • Sandwich ELISA formats for improved sensitivity in complex matrices

• Lateral Flow Immunoassays:

  • Point-of-care rapid tests for detecting UPF0316 in catheter infections

  • Gold nanoparticle-conjugated antibodies for visual detection

  • Multiplex systems targeting UPF0316 alongside established biomarkers

  • Smartphone-readable formats for quantitative assessment

• Immunofluorescence Techniques:

  • Direct visualization of UPF0316 expression in biofilm structures

  • Fluorescently labeled antibodies for confocal microscopy

  • Co-localization studies with other biofilm components

  • Quantitative image analysis correlating expression with infection severity

Molecular Detection Strategies:

• PCR-Based Methodologies:

  • Quantitative real-time PCR targeting the SE_1595 gene

  • Digital PCR for absolute quantification in low-abundance samples

  • Multiplex PCR panels including SE_1595 and other virulence markers

  • Loop-mediated isothermal amplification (LAMP) for resource-limited settings

• Next-Generation Sequencing Applications:

  • Targeted amplicon sequencing of SE_1595 for strain typing

  • Metagenomics approaches for detecting SE_1595 in polymicrobial infections

  • RNA-Seq for assessing active transcription in biofilm infections

  • Nanopore sequencing for rapid identification in clinical settings

Biosensor Technologies:

• Electrochemical Biosensors:

  • Impedance-based detection of UPF0316 using specific antibodies

  • Amperometric biosensors with enzyme-labeled detection systems

  • Screen-printed electrodes for point-of-care applications

  • Graphene-modified sensors for enhanced sensitivity

• Aptamer-Based Detection:

  • Selection of specific aptamers against UPF0316

  • Fluorescence resonance energy transfer (FRET) aptasensors

  • Electrochemical aptasensors for quantitative detection

  • Conformational switching aptamers for reagentless detection

Diagnostic Performance Comparison:

Clinical Applications Matrix:

• Catheter-Related Bloodstream Infections:

  • Direct sampling from catheter surfaces

  • Distinction between colonization and infection

  • Correlation with biofilm formation potential

• Prosthetic Joint Infections:

  • Sonication fluid analysis for biofilm detection

  • Antibody-based imaging for localization

  • UPF0316 expression patterns as virulence indicators

• Wound Infections:

  • Swab-based rapid tests for colonization assessment

  • Monitoring treatment efficacy through quantitative measurements

  • Distinguishing between commensal and pathogenic strains

The development of UPF0316-based diagnostics could significantly improve detection of S. epidermidis infections, particularly in distinguishing between A/C cluster strains (more associated with nosocomial infections) and B cluster strains (more commonly commensal) . This differentiation is clinically valuable for determining appropriate treatment strategies and avoiding unnecessary antibiotic use in cases of non-pathogenic colonization.