Recombinant Aliivibrio salmonicida UPF0761 membrane protein VSAL_I2938 (VSAL_I2938)

What is VSAL_I2938 and why is it significant for research?

VSAL_I2938 is a UPF0761 family membrane protein found in Aliivibrio salmonicida (strain LFI1238), previously classified as Vibrio salmonicida. The protein consists of 310 amino acids and has a UniProt accession number of B6EGQ7 . The significance of this protein lies in its potential role in bacterial membrane function and possible involvement in pathogenicity mechanisms of A. salmonicida, a known fish pathogen.

The amino acid sequence reveals characteristic features of integral membrane proteins, including multiple hydrophobic regions that likely form transmembrane domains. The sequence (MEEKFKYSLRISWSYFLFLKQRIIHDRLTVSAGYMAYITLLSLVPLVTVLLSVLSQFPIFSGAGETVQEFVIQNFVPAAS DAVEGSLFISNTGKMTAVGSGFLFVASVMLISAIDRS...) suggests a complex tertiary structure with potential functional domains . Studying VSAL_I2938 provides insights into membrane protein evolution, bacterial adaptation mechanisms, and potential targets for antibacterial interventions in aquaculture settings.

How does VSAL_I2938 compare to other UPF0761 family proteins?

When comparing VSAL_I2938 to other UPF0761 family proteins such as E. coli's YihY protein, researchers can observe both structural similarities and species-specific adaptations. The E. coli UPF0761 membrane protein YihY (UniProt ID: B7L9D9) consists of 290 amino acids compared to VSAL_I2938's 310 amino acids . Both proteins share characteristic hydrophobic regions and predicted transmembrane domains typical of the UPF0761 family.

These comparative analyses provide valuable insights into the evolutionary conservation of UPF0761 family proteins across different bacterial species and their potential functional significance .

What expression systems are most suitable for recombinant VSAL_I2938 production?

For prokaryotic expression systems (such as E. coli):

• Codon optimization is essential due to potential codon bias between A. salmonicida and the expression host

• Fusion tags (particularly His-tags) facilitate purification and can enhance solubility

• Selection of appropriate promoters (such as T7) and host strains (such as BL21(DE3)) optimized for membrane protein expression

• Growth at lower temperatures (16-20°C) after induction to reduce inclusion body formation

• Addition of specific membrane-mimicking environments or detergents during expression

For eukaryotic expression systems (when prokaryotic systems prove challenging):

• Yeast (Pichia pastoris) systems can provide a more native-like membrane environment

• Insect cell systems may be advantageous for larger membrane protein complexes

• Mammalian cell systems might be necessary if post-translational modifications are critical

The storage and handling of the expressed protein should follow established protocols, including storage at -20°C or -80°C with 50% glycerol to maintain stability, and avoidance of repeated freeze-thaw cycles that can damage the protein structure .

How can researchers overcome challenges in membrane protein expression for VSAL_I2938?

Expression of membrane proteins like VSAL_I2938 presents significant challenges due to their hydrophobic nature, potential toxicity to host cells, and complex folding requirements. Implementing specialized strategies is essential for successful production:

Addressing translation initiation problems:

• Design constructs with fusion tags on both N and C termini to identify full-length proteins and distinguish them from truncated products

• Implement a stepwise imidazole gradient during purification to separate truncated products from full-length proteins

• Optimize the ribosome binding site and distance from the start codon to enhance translation initiation efficiency

Overcoming protein toxicity:

• Utilize tightly controlled inducible promoter systems (such as the lac or tet promoters)

• Employ expression hosts specifically engineered for toxic protein expression (C41/C43 strains)

• Consider cell-free protein synthesis systems for highly toxic membrane proteins

• Implement a leaky expression system with lower induction levels over longer periods

Enhancing membrane protein folding:

• Co-express molecular chaperones (GroEL/GroES, DnaK/DnaJ) to assist with protein folding

• Include specific lipids or detergents in the growth medium

• Express the protein as a fusion with highly soluble partners (MBP, SUMO, or TrxA)

• Select an expression temperature that balances protein production rate with proper folding (typically 16-20°C)

Researchers should systematically optimize these parameters through small-scale expression trials before proceeding to larger-scale production, monitoring protein expression using techniques such as Western blotting with antibodies against the fusion tags .

What purification strategies yield the highest purity and activity for VSAL_I2938?

Purifying membrane proteins like VSAL_I2938 requires specialized approaches to maintain structural integrity and functional activity. A systematic purification strategy should include:

Membrane extraction and solubilization:

• Harvest cells and disrupt by sonication or homogenization in appropriate buffer systems

• Isolate membrane fractions through differential centrifugation

• Solubilize membrane proteins using detergents appropriate for downstream applications

  • Mild detergents (DDM, LMNG) for functional studies

  • Stronger detergents (SDS, Triton X-100) for maximum extraction but potential denaturation

• Optimize detergent:protein ratios through small-scale trials

Affinity chromatography and further purification:

• Utilize His-tag affinity chromatography as the initial capture step

  • Implement stepwise imidazole gradient (20-300mM) to minimize non-specific binding

  • Include appropriate detergents in all buffers to maintain protein solubility

• Consider secondary purification steps:

  • Size exclusion chromatography to remove aggregates and ensure homogeneity

  • Ion exchange chromatography for further purification if isoelectric point allows

• Monitor purity through SDS-PAGE and Western blotting

Maintaining protein stability post-purification:

• Store in buffer containing Tris/PBS, 50% glycerol at pH 8.0

• Add stabilizing agents such as specific lipids or mild detergents

• Aliquot to avoid freeze-thaw cycles and store at -20°C or -80°C

• For functional studies, reconstitute in lipid bilayers or nanodiscs to maintain native-like environment

Validation of protein activity should be performed using functional assays specific to predicted activities of UPF0761 family proteins, potentially including transport assays or binding studies with predicted interaction partners .

What analytical techniques are most effective for characterizing VSAL_I2938 structure and function?

Comprehensive characterization of VSAL_I2938 requires multiple complementary techniques addressing different aspects of protein structure and function:

Structural characterization:

• Circular Dichroism (CD) spectroscopy:

  • Provides information on secondary structure content (α-helices, β-sheets)

  • Useful for monitoring structural changes under different conditions

• Cryo-Electron Microscopy (Cryo-EM):

  • Increasingly powerful for membrane protein structure determination

  • Can visualize protein in a near-native lipid environment

• X-ray crystallography (challenging but valuable):

  • Requires successful crystallization, often using lipidic cubic phase methods

  • Provides atomic-level resolution if successful

• Nuclear Magnetic Resonance (NMR) spectroscopy:

  • Applicable for specific domains or in detergent micelles

  • Provides dynamic information not available from static methods

Functional characterization:

• Liposome reconstitution assays:

  • Incorporate purified protein into liposomes to assess transport function

  • Can use fluorescent probes to monitor substrate movement

• Microscale Thermophoresis (MST) or Surface Plasmon Resonance (SPR):

  • Determine binding affinities for potential substrates or interaction partners

  • Allow quantitative assessment of protein-protein interactions

• Electrophysiology techniques:

  • For potential channel or transporter functions

  • Can be combined with site-directed mutagenesis to identify functional residues

Computational approaches:

• Molecular dynamics simulations to predict protein behavior in membranes

• Homology modeling based on related UPF0761 family proteins

• Protein-protein interaction prediction tools to identify potential binding partners

Through strategic combination of these techniques, researchers can develop a comprehensive understanding of VSAL_I2938's structural features and functional mechanisms in bacterial membranes.

How can VSAL_I2938 be used in fish pathogen research?

VSAL_I2938 from Aliivibrio salmonicida presents valuable opportunities for studying fish pathogens, particularly in the context of cold-water vibriosis in salmonid aquaculture. Researchers can leverage this protein through multiple experimental approaches:

Virulence and pathogenicity studies:

• Generate VSAL_I2938 knockout or knockdown strains of A. salmonicida

  • Assess changes in bacterial growth, survival, and pathogenicity

  • Compare wild-type and mutant strains in infection models

• Overexpress VSAL_I2938 to evaluate potential changes in virulence factors

• Investigate its role in biofilm formation using crystal violet assays and microscopy

• Assess temperature-dependent expression patterns correlating with disease outbreaks

Immunological applications:

• Use purified recombinant VSAL_I2938 to:

  • Develop specific antibodies for diagnostic applications

  • Create ELISA-based detection systems for A. salmonicida

  • Study host immune responses to specific bacterial membrane components

• Evaluate potential as a vaccine component:

  • Assess immunogenicity in model systems

  • Determine protective efficacy in challenge studies

  • Investigate adjuvant combinations to enhance immune responses

Comparative analyses across fish pathogens:

• Examine conservation of UPF0761 family proteins across various fish pathogens

• Correlate structural variations with host specificity or virulence differences

• Use as a molecular marker for evolutionary studies of fish pathogens

These approaches can yield valuable insights for aquaculture disease management and contribute to fundamental understanding of host-pathogen interactions in marine environments.

What methods should be used to study VSAL_I2938 interactions with host cells or other bacterial proteins?

Investigating VSAL_I2938's interactions with host cells or other bacterial proteins requires specific methodological approaches that accommodate its membrane-bound nature:

For protein-protein interactions:

• Proximity-based labeling methods:

  • BioID or APEX2 fusion proteins to identify proximal proteins in vivo

  • Can capture transient interactions in native membrane environments

• Co-immunoprecipitation with membrane-specific modifications:

  • Use crosslinking agents to stabilize transient interactions

  • Employ detergent optimization to maintain complex integrity

  • Validate with reverse co-IP and western blotting analysis

• Yeast two-hybrid adaptations for membrane proteins:

  • Split-ubiquitin membrane yeast two-hybrid system

  • MYTH (membrane yeast two-hybrid) system

• Fluorescence-based interaction assays:

  • FRET (Förster Resonance Energy Transfer) for direct interaction detection

  • BiFC (Bimolecular Fluorescence Complementation) for visualizing interactions in situ

For host-pathogen interaction studies:

• Cell culture models using fish cell lines:

  • Assess binding to specific cell types

  • Evaluate cellular responses to purified VSAL_I2938

• Fluorescently-labeled protein tracking:

  • Monitor localization during infection processes

  • Identify potential host cell receptors

• Proteomics approaches:

  • Crosslink VSAL_I2938 to host cell proteins during infection

  • Mass spectrometry identification of interaction partners

Data analysis approaches:

• Implement network analysis to map interaction landscapes

• Utilize computational docking to predict binding interfaces

• Develop quantitative binding assays to determine affinity constants

• Perform coevolutionary analysis to identify potential interaction partners

When interpreting interaction data, researchers should consider the physiological relevance of detected interactions and validate key findings through multiple complementary approaches.

How can comparative analysis of UPF0761 family proteins enhance understanding of bacterial adaptation mechanisms?

Comparative analysis of UPF0761 family proteins across bacterial species provides a powerful framework for understanding bacterial adaptation to diverse environments. For VSAL_I2938 research, this approach offers several valuable strategies:

Sequence-based comparative analyses:

• Multiple sequence alignment of UPF0761 family proteins:

  • Identify conserved domains suggesting critical functional regions

  • Detect variable regions potentially associated with species-specific adaptations

  • Compare VSAL_I2938 (A. salmonicida) with YihY (E. coli) to identify marine-specific features

• Phylogenetic analysis to trace evolutionary relationships:

  • Construct phylogenetic trees based on UPF0761 sequences

  • Correlate sequence divergence with ecological niches

  • Identify potential horizontal gene transfer events

Structure-function comparative studies:

• Homology modeling based on available structures:

  • Generate structural models of VSAL_I2938 and related proteins

  • Compare predicted structural features across environmental isolates

• Domain swapping experiments:

  • Create chimeric proteins combining domains from different UPF0761 family members

  • Assess functional changes to identify domain-specific activities

• Site-directed mutagenesis of conserved residues:

  • Target highly conserved amino acids for mutation

  • Evaluate functional consequences to identify critical residues

Environmental adaptation analysis:

• Compare UPF0761 proteins from bacteria adapted to different temperatures:

  • Cold-adapted (psychrophilic) species like A. salmonicida

  • Mesophilic species like E. coli

  • Thermophilic species if available

• Examine responses to environmental stressors:

  • Expression patterns under osmotic stress

  • Regulation during temperature shifts

  • Role in biofilm formation across species

This comparative approach can reveal how membrane proteins evolve to support bacterial adaptation to specific niches, potentially identifying molecular mechanisms that enable pathogenicity in specific environments .

How should researchers interpret contradictory results in VSAL_I2938 functional studies?

Contradictory results in VSAL_I2938 functional studies can stem from multiple factors. Researchers should implement a systematic troubleshooting approach:

Sources of experimental variation to consider:

• Expression system differences:

  • Expression host (E. coli vs. other systems) may affect protein folding

  • Fusion tags can influence protein behavior and interaction profiles

  • Growth conditions (temperature, media composition) impact protein quality

• Purification and handling variables:

  • Detergent selection may alter protein conformation and activity

  • Buffer composition can significantly impact functional assays

  • Storage conditions and freeze-thaw cycles may cause activity loss

• Experimental assay considerations:

  • Sensitivity and specificity of detection methods

  • Physiological relevance of in vitro conditions

  • Potential interference from contaminants or buffer components

Systematic resolution strategies:

• Standardize experimental protocols:

  • Create detailed standard operating procedures

  • Document all variables that might impact results

  • Implement internal controls for each experiment

• Validate protein quality:

  • Confirm full-length protein expression via Western blotting

  • Assess protein homogeneity through size exclusion chromatography

  • Verify proper folding using circular dichroism or fluorescence spectroscopy

• Employ orthogonal approaches:

  • Test function using multiple independent assays

  • Validate key findings in different experimental systems

  • Develop structure-function correlations to explain discrepancies

When publishing, researchers should transparently report all experimental conditions and acknowledge limitations, allowing the scientific community to properly contextualize and build upon findings .

What troubleshooting approaches are effective for VSAL_I2938 expression and purification challenges?

Membrane proteins like VSAL_I2938 frequently present expression and purification challenges. Implementing a methodical troubleshooting workflow can overcome these obstacles:

Low expression yield troubleshooting:

• Sequence optimization:

  • Check for rare codons and optimize if necessary

  • Verify correct reading frame and start/stop codons

  • Ensure appropriate ribosome binding site placement

• Expression conditions optimization:

  • Test multiple induction temperatures (16°C, 20°C, 25°C, 30°C)

  • Vary inducer concentration (IPTG: 0.1-1.0 mM range)

  • Explore different media formulations (LB, TB, auto-induction)

  • Adjust induction duration (4h to overnight)

• Expression strain selection:

  • Test specialized strains (C41/C43, Rosetta, Origami)

  • Consider strains with additional tRNAs for rare codons

  • Evaluate strains with reduced protease activity

Protein solubility and purification issues:

• Detergent screening matrix:

  • Test mild detergents (DDM, LMNG) to harsh detergents (SDS)

  • Optimize detergent concentration for membrane solubilization

  • Consider detergent mixtures for enhanced extraction

• Buffer optimization:

  • Vary pH range (7.0-8.5) for optimal stability

  • Test different salt concentrations (100-500 mM NaCl)

  • Add stabilizing agents (glycerol, specific lipids)

• Chromatography troubleshooting:

  • For His-tag purification: optimize imidazole concentration in wash steps

  • For size exclusion: ensure appropriate column selection for membrane proteins

  • Consider on-column detergent exchange during purification

Protein degradation issues:

• Add protease inhibitors throughout purification process

• Reduce purification time and maintain cold temperatures

• Test different storage conditions and cryoprotectants

• Consider adding specific lipids to maintain protein stability

Systematic documentation of all troubleshooting steps creates valuable protocols for future work with VSAL_I2938 and related membrane proteins.

How can researchers validate antibodies against VSAL_I2938 for experimental applications?

Developing and validating antibodies against membrane proteins like VSAL_I2938 requires rigorous characterization before application in experimental settings. The following systematic approach ensures antibody specificity and reliability:

Validation strategies for anti-VSAL_I2938 antibodies:

• Specificity testing:

  • Western blot analysis using recombinant VSAL_I2938 as positive control

  • Include related UPF0761 family proteins (e.g., E. coli YihY) to assess cross-reactivity

  • Test against knockout/knockdown bacteria as negative controls

  • Examine specificity across different bacterial species and strains

• Epitope mapping:

  • Identify the specific epitope recognition using peptide arrays

  • Confirm accessibility of epitopes in the native protein context

  • Ensure epitopes are not in transmembrane regions unless antibodies are for denatured applications

• Application-specific validation:

  • For immunoprecipitation: optimize detergent conditions

  • For immunofluorescence: verify against overexpression and knockout controls

  • For ELISA: determine optimal antibody concentration and dynamic range

Quantitative validation parameters:

• Sensitivity measurements:

  • Determine limit of detection using purified protein dilution series

  • Assess signal-to-noise ratio in relevant experimental contexts

• Reproducibility assessment:

  • Test antibody performance across multiple protein preparations

  • Evaluate lot-to-lot consistency for polyclonal antibodies

  • Assess stability after multiple freeze-thaw cycles

Documentation requirements:

• Comprehensive validation data should include:

  • Full blot images showing all bands and molecular weight markers

  • Controls demonstrating specificity

  • Quantitative measures of sensitivity and reproducibility

• Catalog all validation conditions:

  • Sample preparation methods

  • Antibody dilutions and incubation conditions

  • Detection systems and image acquisition parameters

Proper antibody validation ensures reliable experimental outcomes and reproducibility in VSAL_I2938 research, particularly important given the challenges associated with membrane protein detection.

What emerging technologies could advance VSAL_I2938 research?

Emerging technologies offer new opportunities to overcome traditional challenges in membrane protein research, potentially revolutionizing studies of VSAL_I2938:

Advanced structural biology approaches:

• Cryo-EM innovations:

  • Single-particle analysis with improved detectors and processing algorithms

  • Microcrystal electron diffraction for membrane proteins resistant to traditional crystallization

  • In situ structural determination within native membrane environments

• Integrative structural biology:

  • Combining multiple techniques (X-ray, NMR, SAXS, computational modeling)

  • Mass spectrometry-based structural proteomics to map topology

  • Cross-linking mass spectrometry to identify interaction surfaces

Membrane mimetic systems:

• Nanodiscs and lipid bilayer systems:

  • Improved membrane scaffold proteins for better stability

  • Customizable lipid composition to mimic A. salmonicida membranes

  • High-throughput reconstitution platforms for functional studies

• Cell-free expression systems:

  • Direct integration into artificial membranes during synthesis

  • Reduction of toxicity issues encountered in cellular systems

  • Incorporation of unnatural amino acids for specialized studies

Computational and AI-driven approaches:

• AlphaFold2 and similar AI platforms:

  • Improved prediction of membrane protein structures

  • Application to protein-protein interaction modeling

  • Integration with molecular dynamics simulations

• Deep mutational scanning:

  • Comprehensive mapping of sequence-function relationships

  • Identification of residues critical for stability and function

  • Evolutionary analysis of adaptation mechanisms

Gene editing and synthetic biology:

• CRISPR-Cas9 applications in A. salmonicida:

  • Precise genome editing to study VSAL_I2938 in native context

  • Creation of reporter fusions for in vivo tracking

  • Development of conditional expression systems

• Minimal synthetic membrane systems:

  • Bottom-up construction of functional membrane units

  • Testing isolated functions in defined environments

These emerging technologies promise to accelerate understanding of VSAL_I2938's structure, function, and role in bacterial pathogenicity .

What are the potential applications of VSAL_I2938 research in broader scientific contexts?

Research on VSAL_I2938 extends beyond its specific role in A. salmonicida and can contribute to multiple scientific disciplines:

Comparative bacterial membrane biology:

• Model system for cold-adapted membrane protein function:

  • Understanding how psychrophilic bacteria maintain membrane fluidity

  • Identifying structural adaptations for function at low temperatures

  • Comparing with mesophilic and thermophilic homologs for evolutionary insights

• Membrane protein evolution across bacterial lineages:

  • Tracing the evolutionary history of UPF0761 family proteins

  • Identifying selective pressures on membrane proteins in different environments

  • Understanding horizontal gene transfer patterns of membrane protein genes

Biotechnology applications:

• Membrane protein engineering platforms:

  • Development of stable membrane protein scaffolds for biotechnology

  • Designer transport proteins for controlled molecular passage

  • Creation of membrane-based biosensors

• Bioremediation and environmental monitoring:

  • Adaptations of membrane proteins for extreme conditions

  • Potential applications in bioremediation technologies

  • Biosensors for environmental toxin detection

Aquaculture disease management:

• Novel therapeutic target development:

  • Identification of inhibitors specifically targeting VSAL_I2938

  • Development of antimicrobial strategies targeting membrane vulnerabilities

  • Combination approaches targeting multiple membrane components

• Diagnostic improvements:

  • Molecular markers for rapid pathogen detection

  • Serological tests based on membrane protein antibodies

  • Differentiation between pathogenic and non-pathogenic strains

Fundamental membrane biophysics:

• Model systems for membrane protein folding and stability:

  • Insights into membrane protein topology determination

  • Understanding lipid-protein interactions in bacterial membranes

  • Principles of transmembrane domain packing and stability

Broad application of VSAL_I2938 research underscores the value of studying specialized membrane proteins from diverse bacterial species, with implications extending far beyond the initial research context.

How might VSAL_I2938 research contribute to addressing antibiotic resistance in aquaculture?

The study of VSAL_I2938 and similar membrane proteins may offer novel approaches to combat antibiotic resistance, a growing concern in aquaculture:

Novel therapeutic target identification:

• Membrane vulnerability exploitation:

  • Target membrane proteins essential for bacterial survival

  • Develop compounds that specifically disrupt VSAL_I2938 function

  • Create combination therapies targeting multiple membrane components

• Structure-based drug design:

  • Utilize VSAL_I2938 structural information to design specific inhibitors

  • Develop peptidomimetics that interfere with membrane protein assembly

  • Screen for compounds that destabilize bacterial membranes

Alternative therapeutic strategies:

• Anti-virulence approaches:

  • Target membrane proteins involved in virulence factor secretion

  • Develop compounds that inhibit biofilm formation

  • Create therapies that don't kill bacteria but reduce pathogenicity

• Immune-based strategies:

  • Develop vaccines targeting conserved epitopes of membrane proteins

  • Create immunomodulatory approaches enhancing host resistance

  • Implement passive immunization using antibodies against key membrane targets

Resistance mechanism understanding:

• Membrane-based resistance mechanisms:

  • Study how membrane composition changes affect antibiotic penetration

  • Investigate the role of membrane proteins in efflux pump systems

  • Examine adaptations in membrane proteins following antibiotic exposure

• Cross-resistance patterns:

  • Determine if targeting membrane proteins creates selection pressure

  • Develop strategies to minimize resistance development

  • Design multi-target approaches to reduce resistance emergence

Diagnostic and monitoring applications:

• Early detection systems:

  • Develop rapid tests for antimicrobial resistance markers

  • Create biosensors detecting changes in membrane protein expression

  • Implement surveillance systems in aquaculture settings

• Resistance prediction models:

  • Identify genetic signatures predicting resistance development

  • Create databases linking membrane protein mutations to resistance

  • Develop predictive tools for treatment optimization

These approaches represent promising alternatives to conventional antibiotics, potentially addressing the growing crisis of antimicrobial resistance in aquaculture and beyond.