Recombinant Staphylococcus aureus UPF0316 protein SAS1835 (SAS1835)

What is SAS1835 and what is its relevance in Staphylococcus aureus research?

SAS1835 is a UPF0316 protein found in Staphylococcus aureus, particularly characterized in the MSSA476 strain. The protein is encoded by the SAS1835 gene and consists of 200 amino acid residues. While SAS1835 is classified as an "uncharacterized protein family" (UPF), research on S. aureus proteins is gaining significance due to the pathogen's relevance in human disease and antibiotic resistance concerns .

The amino acid sequence of SAS1835 (MSFVTENPWLMVLTIFIINVCYVTFLTMRTILTLKGYRYIAASVSFLEVLVYIVGLGLVMSNLDHIQNIIAYAFGFSIGIIVGMKIEEKLALGYTVVNVTSAEYELDLPNELRNLGYGVTHYAAFGRDGSRMVMQILTPRKYERKLMDTIKNLDPKAFIIAYEPRNIHGGFWTKGIRRRKLKDYEPEELESVVEHEIQSK) suggests it may function as a membrane-associated protein, given the presence of hydrophobic regions typical of transmembrane domains .

How does SAS1835 compare structurally to other characterized S. aureus proteins?

While SAS1835 remains relatively uncharacterized compared to immunodominant S. aureus proteins like SasG, α-haemolysin, and proteinase SplB, structural analysis indicates it differs significantly from these well-studied virulence factors . Unlike SasG, which contains distinctive A and B domains with the latter featuring repetitive peptide regions that contribute to biofilm formation, SAS1835 appears to have a more uniform structure .

The molecular weight of SAS1835 (approximately 25 kDa based on its amino acid sequence) places it in a different category than the larger adhesins like SasG (~140 kDa) or the medium-sized toxins like α-haemolysin (~35-40 kDa) . This structural distinction suggests that SAS1835 likely plays a different functional role than these established virulence factors.

What are the optimal storage and handling conditions for recombinant SAS1835?

For optimal preservation of recombinant SAS1835 protein activity, the following storage and handling protocols are recommended:

• Long-term storage: Maintain at -20°C or preferably -80°C for extended storage periods

• Working solutions: Store aliquots at 4°C for up to one week only

• Buffer composition: The protein is typically supplied in a Tris-based buffer containing 50% glycerol, optimized for stability

• Avoid freeze-thaw cycles: Repeated freezing and thawing significantly reduces protein activity and should be minimized

For experimental work, it is advisable to prepare small working aliquots to prevent protein degradation from multiple freeze-thaw cycles, and to maintain sterile conditions when handling the protein to prevent microbial contamination.

What experimental approaches are most suitable for investigating SAS1835 function in S. aureus pathogenesis?

To elucidate the function of relatively uncharacterized proteins like SAS1835 in S. aureus pathogenesis, a multi-faceted experimental approach is recommended:

• Gene knockout studies: Generating SAS1835-deficient S. aureus strains through targeted mutagenesis allows assessment of phenotypic changes in virulence, biofilm formation, and antibiotic susceptibility compared to wild-type strains.

• Immunological characterization: Following the methodology used for other S. aureus proteins, researchers can generate antibodies against purified recombinant SAS1835 to evaluate its immunogenicity and potential as a vaccine component .

• Biofilm assays: Given that certain S. aureus surface proteins like SasG significantly affect biofilm formation, similar assays can be performed with SAS1835 antibodies to determine if they inhibit biofilm development. The crystal violet staining technique (0.1% w/v crystal violet followed by 30% acetic acid destaining) can be employed as described for other S. aureus proteins .

• Localization studies: Immunofluorescence or electron microscopy using anti-SAS1835 antibodies can determine the cellular localization of the protein, providing insights into its potential function.

• Protein-protein interaction analyses: Pull-down assays or yeast two-hybrid screens can identify binding partners of SAS1835, elucidating its role in bacterial physiological networks.

How can recombinant SAS1835 be effectively expressed and purified for structural studies?

For high-yield expression and purification of recombinant SAS1835, the following optimized protocol can be implemented:

• Expression system selection: Based on successful approaches with other S. aureus proteins, E. coli Rosetta (DE3) strain is recommended for heterologous expression to address codon usage bias issues .

• Vector construction: Molecular cloning should utilize expression vectors like pET-28a/b or pMal-c5x, which allow fusion with affinity tags (His-tag or MBP-tag) to facilitate purification .

• Cloning strategy:

  • PCR-amplify the SAS1835 gene using primers designed based on the S. aureus genomic sequence

  • Digest with appropriate restriction enzymes (e.g., BamHI/SalI)

  • Ligate into the prepared expression vector

  • Verify construct by restriction analysis and sequencing

• Protein expression optimization:

  • Culture transformed E. coli in appropriate media (e.g., LB with suitable antibiotics)

  • Induce protein expression with IPTG at optimal conditions (typically 0.5-1 mM IPTG at 16-30°C for 4-16 hours)

  • Harvest cells by centrifugation

• Purification workflow:

  • Lyse cells using sonication or French press in appropriate buffer

  • Clarify lysate by centrifugation

  • Perform affinity chromatography (Ni-NTA for His-tagged protein or amylose resin for MBP-tagged protein)

  • Apply secondary purification steps as needed (ion exchange or size exclusion chromatography)

  • Assess purity by SDS-PAGE and Western blot analysis

• Protein quality assessment:

  • Verify identity by mass spectrometry

  • Confirm proper folding using circular dichroism spectroscopy

  • Validate activity through appropriate functional assays

What is the potential role of SAS1835 in vaccine development against S. aureus infections?

While SAS1835's specific role in vaccine development remains to be fully characterized, several considerations can guide research in this direction:

• Immunogenicity assessment: The immunodominance of a protein is a critical factor for vaccine development. While proteins like SasG, α-haemolysin, and proteinase SplB have been identified as highly immunogenic in S. aureus , the immunogenicity of SAS1835 needs to be systematically evaluated through animal immunization studies.

• Multi-component approach: Current research suggests that effective S. aureus vaccines likely require multiple antigenic components . If SAS1835 demonstrates suitable immunogenicity, it could potentially be incorporated into a multi-valent vaccine formulation alongside established immunogens.

• Functional relevance: The efficacy of including SAS1835 in vaccine preparations would depend on its functional role in pathogenesis. If it contributes to virulence or immune evasion, antibodies against it might confer protection.

• Comparative advantage assessment: Researchers should evaluate whether SAS1835 offers advantages over currently studied vaccine candidates. For instance, SasG has shown promise due to its role in biofilm formation , while α-haemolysin is being explored for its critical role in pathogenesis.

• Conservation analysis: The degree of conservation of SAS1835 across clinically relevant S. aureus strains would determine its breadth of coverage as a vaccine component.

What are the best methodological approaches for studying SAS1835 interaction with host immune system components?

To investigate interactions between SAS1835 and the host immune system, researchers should consider the following methodological approaches:

• In vitro binding assays:

  • ELISA-based binding assays to assess interactions with host immune factors

  • Surface plasmon resonance (SPR) to determine binding kinetics and affinities

  • Pull-down assays with host cell lysates to identify potential binding partners

• Immunological studies:

  • Stimulation of immune cells (e.g., macrophages, dendritic cells) with purified SAS1835 to measure cytokine production

  • Flow cytometry to evaluate binding to specific immune cell populations

  • T-cell activation assays to assess MHC presentation of SAS1835-derived peptides

• Antibody response characterization:

  • Immunize experimental animals (mice or rabbits) with purified recombinant SAS1835 following established protocols (20 μg protein per injection with appropriate adjuvant)

  • Collect sera at regular intervals to monitor antibody titer development

  • Characterize antibody subclasses and epitope specificity

  • Evaluate functional activity of antibodies in neutralization or opsonophagocytosis assays

• Ex vivo infection models:

  • Use human blood or tissue explants to assess the impact of anti-SAS1835 antibodies on bacterial survival and immune cell recruitment

  • Employ whole blood killing assays to evaluate opsonophagocytic activity

How can researchers effectively evaluate SAS1835's contribution to biofilm formation?

Biofilm formation is a critical virulence mechanism for S. aureus, and the role of surface proteins in this process is well-established . To specifically evaluate SAS1835's potential contribution to biofilm development, researchers can employ the following methods:

• Crystal violet biofilm assay:

  • Grow S. aureus (wild-type and SAS1835 mutant strains) in appropriate media (e.g., Brain Heart Infusion/Yeast Extract) at 37°C

  • Dilute overnight culture 1:100 in fresh medium and dispense into 96-well plates

  • Add serial dilutions of anti-SAS1835 antibodies or control sera

  • Incubate overnight at 37°C

  • Stain biofilms with 0.1% crystal violet

  • Destain with 30% acetic acid

  • Measure absorbance at 560 nm to quantify biofilm mass

• Confocal laser scanning microscopy (CLSM):

  • Grow biofilms on appropriate surfaces (glass coverslips or flow cells)

  • Stain with fluorescent dyes (e.g., SYTO9/propidium iodide for live/dead staining)

  • Visualize biofilm architecture using CLSM

  • Perform quantitative analysis of biofilm parameters (thickness, biomass, roughness)

• Comparative analysis:

  • Compare SAS1835's effect with known biofilm-promoting factors like SasG

  • Include positive controls (anti-SasG antibodies) and negative controls (pre-immune sera) in experiments

  • Test multiple S. aureus strains to assess strain-specific effects

• Gene expression studies:

  • Monitor expression of SAS1835 during different phases of biofilm development using qRT-PCR

  • Analyze correlation between SAS1835 expression and biofilm maturation

What are the common challenges in purifying functional recombinant SAS1835 and how can they be addressed?

Researchers commonly encounter several technical challenges when purifying recombinant S. aureus proteins like SAS1835. Based on experiences with similar proteins, the following issues and solutions are recommended:

How can researchers troubleshoot inconsistent results in SAS1835 immunogenicity studies?

Immunogenicity studies with bacterial proteins like SAS1835 can yield variable results. Based on experiences with other S. aureus proteins, the following troubleshooting approaches are recommended:

• Antibody production variability:

  • Ensure consistent protein preparation (purity >95% by SDS-PAGE)

  • Validate protein conformation before immunization

  • Standardize adjuvant selection and immunization protocol

  • Consider genetic background variations in animal models

  • Increase sample size to account for individual variation

• Bioassay inconsistencies:

  • Standardize bacterial growth conditions (media, temperature, growth phase)

  • Verify antibody titers before functional assays

  • Include multiple positive and negative controls

  • Develop standard curves for quantitative assays

  • Test multiple bacterial strains to account for strain-specific effects

• Inter-laboratory variations:

  • Establish detailed standard operating procedures

  • Develop reference standards for key reagents

  • Implement regular proficiency testing

  • Consider multi-center validation studies for critical findings

How does SAS1835 compare functionally with well-characterized S. aureus surface proteins like SasG?

While detailed functional studies on SAS1835 are still emerging, comparison with well-characterized S. aureus surface proteins like SasG can provide valuable context:

What is the current understanding of SAS1835's role compared to established S. aureus virulence factors?

The role of SAS1835 in S. aureus pathogenesis remains less defined compared to established virulence factors. Current research on S. aureus has primarily focused on:

• α-haemolysin (Hla): A 35-40 kDa toxin that forms pores in host cell membranes, causing cell lysis. It has been extensively studied as a vaccine component and shows strong immunogenicity .

• SasG: A ~140 kDa surface adhesin that significantly contributes to biofilm formation. Antibodies against SasG can inhibit biofilm development, making it a promising target for anti-biofilm therapeutics and vaccines .

• Proteinases (e.g., SplB): Secreted enzymes that degrade host proteins and contribute to tissue invasion. These are also immunodominant antigens recognized during infection .

• Other surface proteins: Various adhesins, immune evasion proteins, and toxins have defined roles in S. aureus pathogenesis and have been studied as vaccine candidates .

In contrast, SAS1835 belongs to an uncharacterized protein family (UPF0316), and its specific contributions to virulence, biofilm formation, or immune evasion require further investigation. Its relatively smaller size and predicted membrane association suggest it may play a specialized role distinct from the major virulence factors.

What are the most promising research avenues for elucidating SAS1835 function in S. aureus biology?

Several promising research directions could significantly advance our understanding of SAS1835's role in S. aureus biology:

• Structural biology approaches:

  • Determine the three-dimensional structure of SAS1835 using X-ray crystallography or cryo-electron microscopy

  • Identify functional domains and potential binding sites

  • Compare structural features with proteins of known function

• Systems biology integration:

  • Analyze SAS1835 expression patterns across different growth conditions, stress responses, and infection models

  • Identify gene regulatory networks associated with SAS1835 expression

  • Employ proteomics to map interaction partners in different physiological states

• Host-pathogen interaction studies:

  • Investigate SAS1835 interactions with host receptors or immune components

  • Assess impact on host cell signaling pathways

  • Evaluate contribution to immune evasion mechanisms

• Translational research applications:

  • Evaluate SAS1835 as a diagnostic biomarker for S. aureus infections

  • Assess potential as a therapeutic target for novel antimicrobials

  • Determine vaccine potential through protective immunity studies

How might SAS1835 contribute to developing novel anti-Staphylococcal therapies?

Based on current understanding of S. aureus pathogenesis and immunology, SAS1835 might contribute to anti-staphylococcal therapy development in several ways:

• Vaccine component potential:

  • If demonstrated to be immunogenic and surface-exposed, SAS1835 could be included in multi-component vaccine formulations

  • Combination with established immunogens like SasG and α-haemolysin might enhance protective efficacy

  • Conservation across strains would need to be established to ensure broad coverage

• Antibody-based therapeutics:

  • Monoclonal antibodies targeting SAS1835 could be developed for passive immunotherapy

  • Similar to approaches being explored with other S. aureus proteins, these could potentially neutralize bacterial functions or promote opsonophagocytosis

• Anti-virulence approaches:

  • If SAS1835 contributes to pathogenesis, small molecule inhibitors could be developed

  • Such inhibitors might reduce virulence without selecting for resistance, unlike conventional antibiotics

• Biofilm disruption strategies:

  • Should SAS1835 play a role in biofilm formation, anti-SAS1835 approaches might complement strategies targeting other biofilm components like SasG

  • This would be particularly valuable for treating chronic or device-associated infections

• Diagnostic applications:

  • Antibodies against SAS1835 could be employed in rapid diagnostic tests

  • Strain-specific variations in SAS1835 might enable differentiation between S. aureus lineages

The development of these approaches depends on further characterization of SAS1835's function, immunogenicity, and conservation across clinically relevant S. aureus strains.

What are the key knowledge gaps regarding SAS1835 that require immediate research attention?

Based on the current state of knowledge about S. aureus proteins and specific information about SAS1835, several critical knowledge gaps should be prioritized for research:

• Functional characterization: Determining the biological function of SAS1835 in S. aureus physiology and pathogenesis is fundamental to understanding its significance.

• Structural analysis: Resolving the three-dimensional structure would provide insights into potential functional domains and interaction surfaces.

• Expression profile: Establishing when and where SAS1835 is expressed during infection and biofilm formation would clarify its role in pathogenesis.

• Immunological properties: Assessing immunogenicity, epitope mapping, and protective potential of antibodies against SAS1835 is essential for vaccine considerations.

• Conservation analysis: Determining sequence conservation across diverse S. aureus clinical isolates would inform potential breadth of coverage for therapeutic applications.

• Interaction network: Identifying host and bacterial proteins that interact with SAS1835 would elucidate its role in infection processes.

What standardized methodologies should researchers adopt when studying SAS1835 to ensure comparable results?

To advance research on SAS1835 and ensure comparability of results across different laboratories, the following standardized methodologies are recommended:

• Protein production protocols:

  • Consensus expression constructs with defined boundaries and tags

  • Standardized purification protocols with quality control benchmarks

  • Reference standards for protein activity and conformation

• Immunological assays:

  • Standardized immunization protocols with defined adjuvants

  • Reference antibody preparations for assay calibration

  • Validated ELISA and Western blot protocols

• Functional assays:

  • Consensus protocols for biofilm formation assessment

  • Standardized host-pathogen interaction models

  • Agreed-upon reference strains for comparative studies

• Data reporting standards:

  • Minimum information requirements for experimental descriptions

  • Standard formats for sharing raw data

  • Repositories for strain and reagent distribution