Recombinant Staphylococcus aureus UPF0365 protein SaurJH9_1631 (SaurJH9_1631)

How is SaurJH9_1631 classified in protein databases?

SaurJH9_1631 belongs to the UPF0365 protein family, which indicates it's an uncharacterized protein family. In some databases, it's annotated as a flotillin-like protein (FloA), suggesting possible roles in membrane organization. The UniProt ID for this protein is A5ITA1. It is classified among conserved hypothetical proteins in Staphylococcus aureus strain JH9, with homologs present in other S. aureus strains including USA300 (SAUSA300_1533) and other clinical isolates .

What are the optimal conditions for recombinant expression of SaurJH9_1631?

The optimal expression system for SaurJH9_1631 is E. coli with an N-terminal His-tag. The expression vector should contain optimized codons for E. coli usage since S. aureus has a different codon bias. Expression is typically induced at mid-log phase (OD600 of 0.6-0.8) with IPTG concentrations between 0.5-1.0 mM, and cultures are grown at lower temperatures (16-25°C) after induction to improve protein folding .

For membrane-associated proteins like SaurJH9_1631, inclusion of detergents such as n-dodecyl-β-D-maltoside (DDM) at concentrations of 0.1-0.5% during cell lysis and purification helps maintain protein solubility and native conformation .

What purification strategies yield the highest purity for SaurJH9_1631?

A multi-step purification approach yields the highest purity:

• Immobilized metal affinity chromatography (IMAC) using Ni-NTA resin with an imidazole gradient (20-300 mM)

• Size exclusion chromatography to separate monomeric from aggregated protein

• Optional ion-exchange chromatography as a polishing step

To verify full-length protein expression and avoid truncated products, Western blot analysis using antibodies against both N-terminal and C-terminal tags is recommended. Increasing imidazole concentration during elution helps distinguish full-length protein from truncated forms .

What is currently known about the function of SaurJH9_1631 in S. aureus biology?

Current knowledge about SaurJH9_1631 function is limited, but its annotation as a flotillin-like protein (FloA) suggests involvement in membrane organization, potentially creating specialized membrane microdomains. These domains may facilitate the assembly of protein complexes involved in signaling, membrane transport, or virulence factor secretion .

The protein's membrane localization and conservation across different S. aureus strains suggest it plays a fundamental role in bacterial physiology rather than strain-specific functions. Gene proximity analysis in the S. aureus genome indicates possible co-regulation with genes involved in cell membrane integrity and homeostasis .

How can I design experiments to elucidate the function of this uncharacterized protein?

A comprehensive approach to characterizing SaurJH9_1631 function should include:

• Gene deletion studies: Create knockout mutants using CRISPR/Cas9-mediated recombineering as described by Chen et al. to observe phenotypic changes in growth, membrane integrity, and stress responses .

• Protein-protein interaction studies: Use pull-down assays, bacterial two-hybrid systems, or co-immunoprecipitation to identify interaction partners. For membrane proteins like SaurJH9_1631, crosslinking experiments prior to pull-down may be necessary to capture transient interactions .

• Localization studies: Use fluorescent protein fusions or immunofluorescence microscopy to determine subcellular localization and potential co-localization with known membrane microdomains.

• Transcriptomic and proteomic analysis: Compare wild-type and knockout strains under various stress conditions to identify pathways affected by SaurJH9_1631 deletion.

• Structural analysis: Use X-ray crystallography or cryo-EM to determine the three-dimensional structure, which can provide insights into potential functions.

How can I integrate SaurJH9_1631 into S. aureus metabolic models?

To integrate SaurJH9_1631 into metabolic models such as the genome-scale metabolic model of S. aureus USA300_FPR3757 (iSA863), follow these steps:

• Identify potential metabolic pathways associated with membrane organization and lipid metabolism that may involve SaurJH9_1631 based on its flotillin-like properties.

• Create in silico knockouts of SaurJH9_1631 in the model and predict metabolic flux changes under various conditions.

• Validate predictions experimentally by measuring metabolite excretion profiles in wild-type and knockout strains.

• Refine the model based on experimental data using optimization-based reconciliation algorithms similar to those described by Maalik et al. .

The integration of SaurJH9_1631 into metabolic models can help predict its impact on cellular metabolism and identify potential metabolic vulnerabilities that could be targeted for therapeutic development.

What considerations should be made when using recombinant SaurJH9_1631 for antibody production?

When generating antibodies against SaurJH9_1631, consider:

• Epitope selection: Analyze the protein sequence to identify hydrophilic, surface-exposed regions that make good epitopes. Avoid transmembrane domains as they are generally poor immunogens.

• Antigen preparation: Express and purify full-length protein in E. coli with His-tag as described earlier, or alternatively, use synthetic peptides corresponding to predicted antigenic regions.

• Animal models: Rabbits typically produce high-affinity antibodies against bacterial proteins. Consider using two different animal species to generate polyclonal antibodies, enhancing the chances of recognizing different epitopes.

• Validation: Test antibody specificity using Western blot against both recombinant protein and native protein from S. aureus lysates. Include knockout strains as negative controls.

• Cross-reactivity: Check for potential cross-reactivity with homologous proteins from other bacterial species, especially when studying mixed bacterial populations.

How can CRISPR/Cas9 genome editing be optimized for studying SaurJH9_1631 function?

Optimizing CRISPR/Cas9 genome editing for studying SaurJH9_1631 requires a tailored approach:

• Design efficient sgRNAs: Select guide RNAs with high specificity and efficiency using established algorithms. For SaurJH9_1631, target regions away from transmembrane domains to enhance editing efficiency.

• Utilize the two-plasmid system: Employ the temperature-sensitive, two-vector system developed by Chen et al., which enables conditional recombineering and CRISPR/Cas9-mediated counterselection without permanently introducing exogenous genetic material .

• Optimize recombineering oligonucleotides: Design oligonucleotides that:

  • Contain homology arms of 35-40 nucleotides on each side of the target site

  • Include silent mutations that eliminate the PAM site to prevent re-cutting after editing

  • Incorporate additional silent mutations to escape mismatch repair systems

• Control expression timing: Use inducible promoters to control the expression of Cas9 and the recombinase EF2132, which has shown high efficiency in S. aureus .

• Validate edits thoroughly: Confirm genomic changes by sequencing and verify phenotypic effects through complementation studies.

The recombineering efficiency can vary significantly between different S. aureus strains. For example, strain N315 has shown recombineering efficiencies of 2.5 × 10^-3 recombinants per cell, while strain ATCC 29213 showed lower efficiencies of around 10^-4 .

What are the challenges in structural determination of SaurJH9_1631 and how can they be addressed?

Membrane proteins like SaurJH9_1631 present several challenges for structural determination:

• Expression and purification challenges:

  • Overexpression often leads to toxicity or improper folding

  • Solution: Use specialized E. coli strains (C41/C43, Lemo21) designed for membrane protein expression and optimize induction conditions (lower IPTG concentrations, reduced temperature)

• Detergent selection for solubilization:

  • Different detergents can affect protein stability and crystallization

  • Solution: Screen multiple detergents (DDM, LDAO, LMNG) or use amphipols for maintaining protein in solution

• Crystallization difficulties:

  • Membrane proteins often resist forming well-ordered crystals

  • Solution: Consider lipidic cubic phase (LCP) crystallization, which provides a membrane-like environment

• Alternative structural approaches:

  • If crystallization proves challenging, employ cryo-electron microscopy (cryo-EM) which has revolutionized membrane protein structure determination

  • For dynamic regions, nuclear magnetic resonance (NMR) on isotopically labeled protein fragments can provide valuable structural information

• Computational prediction:

  • Use AlphaFold2 or similar AI-based structure prediction tools as a starting point for structural understanding, especially while experimental structures are being pursued

How does SaurJH9_1631 compare across different S. aureus strains and what are the implications for pathogenesis?

Comparative analysis of SaurJH9_1631 homologs across different S. aureus strains reveals important insights:

A comprehensive understanding of these variations and their functional implications requires integrated genomic, transcriptomic, and proteomic approaches, combined with infection models to assess the contribution of SaurJH9_1631 to S. aureus pathogenesis across different clinical isolates.

What are the best approaches for studying membrane protein-protein interactions involving SaurJH9_1631?

Studying membrane protein interactions requires specialized techniques:

• Crosslinking mass spectrometry (XL-MS): Use membrane-permeable crosslinkers like DSS or formaldehyde to capture interactions in vivo, followed by immunoprecipitation and mass spectrometry identification of interaction partners.

• FRET-based approaches: Create fluorescent protein fusions (ensuring they don't disrupt function) to monitor proximity-based interactions in live cells.

• Split-protein complementation assays: Systems like BACTH (Bacterial Adenylate Cyclase Two-Hybrid) have been adapted for membrane protein interaction studies in bacteria.

• Co-purification with mild detergents: Using gentle solubilization conditions that preserve protein-protein interactions during purification, followed by mass spectrometry analysis.

• Liposome reconstitution: Reconstitute purified SaurJH9_1631 with potential interaction partners in artificial liposomes to study direct interactions in a membrane environment.

Each method has strengths and limitations, so a combination of approaches is recommended for confident identification of interaction partners. Validation of key interactions should be performed using targeted approaches like co-immunoprecipitation with specific antibodies.

How can I assess the impact of environmental conditions on SaurJH9_1631 expression and function?

To comprehensively assess environmental regulation of SaurJH9_1631:

• Transcriptional analysis:

  • Use qRT-PCR to measure SaurJH9_1631 mRNA levels under various conditions (pH, osmolarity, nutrient limitation, antibiotics)

  • RNA-seq provides genome-wide context for SaurJH9_1631 regulation within the transcriptome

• Protein level assessment:

  • Western blotting with specific antibodies to quantify protein levels

  • Mass spectrometry-based proteomics for global protein changes

• Promoter activity:

  • Create transcriptional fusions of the SaurJH9_1631 promoter to reporter genes (GFP, luciferase)

  • Monitor activity under different conditions in real-time

• Functional assays:

  • Membrane integrity assays (fluorescent dye uptake, antibiotic sensitivity)

  • Virulence factor secretion and biofilm formation

  • Growth and survival under stress conditions

• In vivo expression:

  • Use animal infection models with reporter systems to monitor expression during pathogenesis

A detailed experimental design might include exposing S. aureus to conditions mimicking different host environments (varying pH, antimicrobial peptides, oxygen limitation) and monitoring changes in SaurJH9_1631 expression, localization, and impact on bacterial physiology when the gene is deleted or overexpressed.