Recombinant Staphylococcus aureus UPF0365 protein SAB1445c (SAB1445c)

What is the structural composition of SAB1445c protein?

SAB1445c is a full-length protein (329 amino acids) from Staphylococcus aureus strain bovine RF122/ET3-1 with UniProt accession number Q2YT06. The amino acid sequence is: MFSLSFIVIAVIIVVALLILFSFVPIGLWISALAAGVHVGIGTLVGMRLRRVSPRKVIAPLIKAHKAGLALTTNQLESHYLAGGNVDRVVDANIAAQRADIDLPFERAAAIDLAGRDVLEAVQMSVNPKVIETPFIAGVAMNGIEVKAKARITVRANIARLVGGAGEETIIARVGEGIVSTIGSSKHHTEVLENPDNISKTVLSKGLDSGTAFEILSIDIADVDISKNIGADLQTEQALADKNIAQAKAEERRAMAVATEQEMKARVQEMHAKVVEAESEVPLAMAEALRSGNISVKDYYNLKNIEADTGMRNAINKRTDQSDDESPEH . Based on the sequence analysis, the protein contains both hydrophobic and hydrophilic regions, suggesting it may be membrane-associated, which has implications for experimental approaches when working with this protein.

What are the optimal storage conditions for recombinant SAB1445c protein?

For short-term storage, recombinant SAB1445c protein should be maintained at 4°C for up to one week. For extended storage, the protein should be kept at -20°C, and for long-term preservation, -80°C is recommended. The protein is typically supplied in a Tris-based buffer containing 50% glycerol, which helps maintain stability. Importantly, repeated freezing and thawing cycles should be avoided as they can lead to protein degradation and loss of functional activity . To mitigate this risk, researchers should consider preparing small working aliquots upon initial thawing to minimize freeze-thaw cycles of the main stock.

How does the amino acid sequence of SAB1445c inform its potential function?

The amino acid sequence of SAB1445c contains regions characteristic of membrane proteins, with hydrophobic stretches potentially forming transmembrane domains. The sequence begins with "MFSLSFIVIAVIIVVALLILFSFVPI," which shows a high concentration of hydrophobic residues typical of membrane-anchoring regions . The protein belongs to the UPF0365 family, where "UPF" designates proteins of unknown function. Bioinformatic analysis suggests potential roles in cell membrane integrity, transport, or signaling based on sequence motifs. Research indicates that S. aureus membrane proteins often contribute to virulence, antibiotic resistance, or adaptation to environmental stressors, such as the copper adaptation mentioned in related research .

What expression systems are most effective for producing recombinant SAB1445c?

For SAB1445c specifically, researchers should consider:

• Using C41/C43 E. coli strains designed for membrane protein expression

• Adding fusion tags at both N- and C-termini to facilitate purification and detection of full-length protein

• Optimizing codon usage for the expression host

• Using low-temperature induction to improve proper folding

• Including appropriate detergents during purification to maintain native structure

How might SAB1445c contribute to S. aureus adaptation to copper stress?

The dissertation mentioned in the search results investigates "molecular adaptation of Staphylococcus aureus to copper Schiff's base at proteome level," suggesting SAB1445c may play a role in copper stress response . While detailed functional data is limited, UPF0365 family proteins could participate in metal homeostasis through several potential mechanisms:

• Membrane-associated metal sensing or transport

• Protection of cellular components from copper toxicity

• Participation in redox reactions to mitigate oxidative stress induced by copper

• Structural reorganization of the cell envelope in response to metal stress

To investigate these possibilities, researchers could employ techniques such as:

• Protein-metal binding assays using isothermal titration calorimetry

• Gene knockout studies comparing wild-type and ΔSAB1445c strains under copper stress

• Transcriptional analysis to identify co-regulated genes in the copper response pathway

• Localization studies using fluorescent tagging to determine if the protein redistributes during copper exposure

What are the challenges in structural determination of SAB1445c and how can they be addressed?

As a membrane-associated protein, SAB1445c presents several challenges for structural determination:

• Protein expression and purification challenges: The hydrophobic regions make it difficult to express in sufficient quantities and maintain solubility during purification .

• Crystallization difficulties: Membrane proteins often resist conventional crystallization approaches needed for X-ray crystallography.

• Conformational heterogeneity: Membrane proteins may adopt multiple conformations, complicating structural analysis.

Methodological approaches to address these challenges include:

• Nanodiscs or lipid cubic phase crystallization: These techniques provide membrane-mimetic environments that can stabilize the protein in its native conformation.

• Cryo-electron microscopy (cryo-EM): This emerging technique can determine structures of membrane proteins without crystallization.

• Protein engineering: Creating fusion constructs with soluble proteins or truncating highly flexible regions can improve protein stability and crystallization propensity.

• NMR spectroscopy with detergent micelles: For smaller membrane proteins or domains, solution NMR with appropriate detergents can provide structural information.

How can protein-protein interaction studies with SAB1445c inform its functional role?

Identifying interaction partners of SAB1445c could provide crucial insights into its biological function. Advanced methods for protein-protein interaction studies suitable for membrane proteins include:

• Split-ubiquitin yeast two-hybrid systems: Unlike conventional yeast two-hybrid, this adaptation works with membrane proteins.

• Proximity-dependent biotin identification (BioID): By fusing SAB1445c to a biotin ligase, nearby proteins become biotinylated and can be identified by mass spectrometry.

• Co-immunoprecipitation with crosslinking: Chemical crosslinking can stabilize transient interactions before cell lysis and immunoprecipitation.

• Surface plasmon resonance (SPR): For testing direct interactions with candidate proteins in vitro.

Analysis should focus on interactions that change under copper stress conditions or other relevant environmental challenges to understand the protein's role in bacterial adaptation mechanisms.

What purification strategies optimize yield and activity of recombinant SAB1445c?

Purifying membrane-associated proteins like SAB1445c requires specialized approaches:

Recommended purification protocol:

• Cell lysis optimization: Use gentle lysis methods (such as enzymatic lysis with lysozyme followed by mild sonication) to preserve protein structure.

• Membrane fraction isolation: Separate membrane fractions through ultracentrifugation (100,000 × g for 1 hour).

• Solubilization: Select appropriate detergents based on the hydrophobicity profile - for SAB1445c, mild detergents like n-dodecyl-β-D-maltoside (DDM) or lauryl maltose neopentyl glycol (LMNG) at 1-2% are recommended for initial trials.

• Affinity chromatography: Utilize the tag incorporated during expression (typically His-tag) for initial purification. For SAB1445c, consider using fusion tags at both termini to ensure isolation of full-length protein only .

• Sequential elution: Increase imidazole concentration gradually (50 mM steps) to separate truncated products from full-length protein .

• Size exclusion chromatography: As a final polishing step to ensure homogeneity and remove aggregates.

• Quality control: Verify integrity through SDS-PAGE, Western blot, and mass spectrometry.

How can researchers effectively assess the functional activity of SAB1445c?

Without established functional assays for this uncharacterized protein, researchers should employ multiple approaches:

• Copper binding assays: If related to copper adaptation, measure copper binding using:

  • Isothermal titration calorimetry (ITC)

  • Differential scanning fluorimetry with copper titration

  • Spectroscopic methods to detect Cu(II) coordination

• Membrane integrity assays: Test if SAB1445c affects membrane properties:

  • Fluorescent dye leakage assays

  • Membrane fluidity measurements

  • Atomic force microscopy to detect structural changes

• Growth and survival assays: Compare wild-type and SAB1445c-deficient strains under various stressors:

  • Copper tolerance

  • Oxidative stress resistance

  • Antimicrobial susceptibility

• Localization studies: Determine subcellular distribution using:

  • Immunogold electron microscopy

  • Fractionation followed by Western blotting

  • Fluorescent protein fusions with confocal microscopy

How does SAB1445c compare to homologous proteins in other Staphylococcus strains?

Understanding evolutionary conservation of SAB1445c provides insight into its importance:

Proteins with high conservation across strains from different hosts suggest fundamental roles in bacterial physiology, while variations might indicate host-specific adaptations. Researchers should analyze these variations in the context of the source (bovine vs. human) and pathogenicity profiles of each strain.

What role might SAB1445c play in S. aureus virulence or antibiotic resistance?

While direct evidence is limited in the search results, membrane proteins in S. aureus often contribute to pathogenicity and antimicrobial resistance. Researchers investigating this connection should consider:

• Expression analysis: Measure SAB1445c expression levels during:

  • Host colonization/infection models

  • Exposure to sub-inhibitory antibiotic concentrations

  • Growth in metal-restricted environments mimicking host conditions

• Virulence assessment: Compare wild-type and SAB1445c mutant strains for:

  • Biofilm formation capacity

  • Adherence to host cells

  • Survival in macrophages

  • Virulence in animal infection models

• Antibiotic susceptibility testing: Determine if SAB1445c affects:

  • Minimum inhibitory concentrations (MICs) of various antibiotics

  • Persistence under antibiotic stress

  • Cell wall/membrane integrity during antibiotic challenge

How might CRISPR-Cas9 techniques advance functional studies of SAB1445c?

CRISPR-Cas9 technology offers powerful approaches for studying SAB1445c:

• Precise gene editing: Create clean deletions, point mutations, or tagged versions of SAB1445c in its native genomic context.

• Conditional expression systems: Develop strains with inducible or repressible SAB1445c expression to study dosage effects.

• CRISPRi approaches: Use deactivated Cas9 (dCas9) to repress SAB1445c expression without genomic modification, allowing temporal control.

• CRISPR screening: Conduct genome-wide screens to identify genetic interactions with SAB1445c, revealing functional pathways.

• Base editing: Introduce specific amino acid changes to test structure-function hypotheses without disrupting the reading frame.

When implementing CRISPR technologies in S. aureus, researchers should optimize transformation protocols for high efficiency and carefully design guide RNAs to minimize off-target effects.

What proteomics approaches would best elucidate SAB1445c's role in S. aureus copper adaptation?

Building on the dissertation research mentioned , advanced proteomics approaches could include:

• Membrane proteome profiling: Compare membrane protein expression between wild-type and SAB1445c-deficient strains under copper stress using stable isotope labeling (SILAC) or tandem mass tag (TMT) labeling.

• Protein-protein interaction network analysis: Use proximity labeling approaches like TurboID combined with mass spectrometry to identify proteins physically close to SAB1445c during copper stress.

• Post-translational modification mapping: Investigate whether SAB1445c undergoes modifications (phosphorylation, glycosylation) in response to copper exposure.

• Targeted metabolomics: Measure changes in copper-related metabolites in SAB1445c mutants to understand downstream effects.

• Spatial proteomics: Use imaging mass spectrometry to visualize protein distribution changes during copper adaptation.