Recombinant Vibrio fischeri UPF0761 membrane protein VFMJ11_0098 (VFMJ11_0098)

What is the UPF0761 membrane protein from Vibrio fischeri?

The UPF0761 membrane protein from Vibrio fischeri is a 310-amino acid transmembrane protein encoded by the VFMJ11_0098 gene in the Vibrio fischeri strain MJ11. This protein belongs to the UPF0761 protein family, a group of uncharacterized membrane proteins found primarily in Gram-negative bacteria. The protein has a UniProt ID of B5FFD1 and is predicted to contain multiple transmembrane domains based on its hydrophobicity profile. While its precise function remains to be fully elucidated, structural analysis suggests it may play a role in membrane integrity, signaling, or transport processes that contribute to the symbiotic relationship between V. fischeri and its host organisms .

How is recombinant VFMJ11_0098 protein typically expressed and purified?

Recombinant VFMJ11_0098 protein is typically expressed in E. coli expression systems using a vector that incorporates an N-terminal His-tag for purification purposes. The expression protocol generally involves:

• Cloning the full-length VFMJ11_0098 gene (encoding amino acids 1-310) into an appropriate expression vector

• Transforming the construct into a specialized E. coli strain optimized for membrane protein expression

• Inducing protein expression under controlled conditions (temperature, inducer concentration, duration)

• Cell lysis using detergents that effectively solubilize membrane proteins

• Purification via immobilized metal affinity chromatography (IMAC) utilizing the His-tag

• Further purification steps such as size exclusion chromatography if higher purity is required

The purified protein is typically obtained in a detergent-solubilized form or reconstituted into liposomes for functional studies. The final product generally achieves greater than 90% purity as determined by SDS-PAGE analysis .

What are the optimal storage conditions for recombinant VFMJ11_0098?

The optimal storage conditions for recombinant VFMJ11_0098 protein are:

It is strongly recommended to avoid repeated freeze-thaw cycles as they can lead to protein denaturation and loss of activity. For optimal results, the lyophilized protein should be briefly centrifuged prior to opening to bring the contents to the bottom of the vial. Reconstitution should be performed using deionized sterile water, and addition of 5-50% glycerol (with 50% being the default recommendation) is advised for long-term storage .

How can I design experiments to study the function of VFMJ11_0098 in host-microbe interactions?

Designing experiments to study the function of VFMJ11_0098 in host-microbe interactions requires a multi-faceted approach:

• Gene knockout/complementation studies:

  • Generate a VFMJ11_0098 deletion mutant in V. fischeri

  • Create a complemented strain expressing the wild-type protein

  • Compare colonization efficiency and host responses in a squid (Euprymna scolopes) model system

• Outer membrane vesicle (OMV) analysis:

  • Isolate OMVs from wild-type and VFMJ11_0098 mutant strains

  • Compare OMV production, size distribution (~30 nm diameter in wild-type), and protein composition

  • Assess differences in biofilm formation capacity between strains

• Host response assessment:

  • Expose host tissues to purified recombinant VFMJ11_0098 or OMVs containing the protein

  • Measure hemocyte trafficking as a readout of host immune response

  • Compare with controls including other Vibrio species OMVs and known MAMPs (microbe-associated molecular patterns)

• True experimental design elements:

  • Include appropriate control groups (vehicle only, heat-inactivated protein)

  • Random assignment of specimens to treatment groups

  • Blinded assessment of outcomes where possible

  • Sufficient biological and technical replicates for statistical validity

This experimental approach follows principles of true experimental design, where the independent variable (presence/absence/mutation of VFMJ11_0098) is manipulated and the dependent variables (colonization, OMV characteristics, host responses) are measured under controlled conditions .

How does the VFMJ11_0098 protein potentially contribute to outer membrane vesicle formation in Vibrio fischeri?

The VFMJ11_0098 protein may contribute to outer membrane vesicle (OMV) formation in Vibrio fischeri through several potential mechanisms:

• Membrane curvature modulation: As a membrane protein with multiple transmembrane domains, VFMJ11_0098 may influence local membrane curvature, which is critical for OMV budding from the outer membrane.

• Protein-lipid interactions: The protein may interact with specific lipid species in the outer membrane, creating domains with altered fluidity or composition that promote vesiculation.

• Interaction with OMV biogenesis machinery: VFMJ11_0098 may form complexes with other proteins involved in OMV biogenesis, contributing to the coordinated process of vesicle formation.

Electron microscopy studies have shown that V. fischeri OMVs average approximately 30 nm in diameter and play important roles in the symbiont's biofilm formation. These OMVs are critical elements in host-cell/microbe interactions, particularly in the symbiotic relationship between V. fischeri and the squid Euprymna scolopes .

To experimentally determine the role of VFMJ11_0098 in OMV formation, researchers could:

• Quantify OMV production in wild-type versus VFMJ11_0098 mutant strains

• Analyze the membrane localization of VFMJ11_0098 during different growth phases

• Identify protein interaction partners using pull-down assays or crosslinking studies

• Assess the impact of VFMJ11_0098 overexpression on membrane integrity and OMV production

These approaches would help elucidate whether VFMJ11_0098 plays a structural, regulatory, or ancillary role in the complex process of OMV biogenesis in V. fischeri .

What bioinformatic approaches can be used to predict functional domains in VFMJ11_0098?

Several bioinformatic approaches can be employed to predict functional domains in the VFMJ11_0098 protein:

• Transmembrane topology prediction:

  • TMHMM, HMMTOP, or Phobius for identifying transmembrane segments

  • SignalP for signal peptide prediction

  • TOPCONS for consensus membrane topology

• Structural homology modeling:

  • I-TASSER or Phyre2 for generating 3D structural models based on remote homologs

  • AlphaFold2 for ab initio protein structure prediction

  • Verification of models using ProSA, VERIFY3D, or PROCHECK

• Functional domain annotation:

  • InterProScan for identifying conserved domains

  • Pfam database searches for protein family membership

  • SMART for architecture-based domain identification

• Evolutionary analysis:

  • Multiple sequence alignment of UPF0761 family members using MUSCLE or T-Coffee

  • Identification of conserved residues using ConSurf

  • Phylogenetic analysis using RAxML or MrBayes

• Protein-protein interaction prediction:

  • STRING database for identifying potential interaction partners

  • PRISM for structural interface-based interaction prediction

Using these approaches, researchers can generate testable hypotheses regarding the functional domains within VFMJ11_0098, which can then be validated through targeted mutagenesis and functional assays. The analysis of the complete amino acid sequence (MEDKIKHKLRIGWSYLLFLKQRVIHDRLTVSAGYMAYITLLSLVPLITVLLSVLSQFPVF...) would form the basis for these predictions .

What controls should be included when studying VFMJ11_0098 function in vitro?

When studying VFMJ11_0098 function in vitro, a comprehensive set of controls should be included to ensure experimental validity:

• Negative controls:

  • Empty vector-expressed protein prepared under identical conditions

  • Heat-denatured VFMJ11_0098 protein to control for non-specific effects

  • Buffer-only conditions to control for buffer components

• Positive controls:

  • Well-characterized membrane protein from the same family (if available)

  • Known functional protein that produces measurable effects in your assay system

• Expression system controls:

  • Protein expressed without the His-tag to control for tag interference

  • Alternative tag system (e.g., GST-tag) to verify consistency of results

  • Protein expressed in different E. coli strains to control for host-specific effects

• Experimental validation controls:

  • Concentration gradient of the protein to establish dose-response relationships

  • Time-course experiments to determine temporal aspects of protein activity

  • Inclusion of specific inhibitors or activators of predicted pathways

• Technical controls:

  • Multiple protein preparations to control for batch-to-batch variation

  • Storage time controls to assess protein stability

  • Detergent/lipid composition controls if protein is reconstituted into membranes

How can I establish a knockout/knockdown system for VFMJ11_0098 in Vibrio fischeri?

Establishing a knockout/knockdown system for VFMJ11_0098 in Vibrio fischeri requires specific molecular genetic approaches suitable for this marine bacterium:

• Gene deletion (knockout) approach:

  a) Allelic exchange method:

  • Design primers to amplify ~1 kb flanking regions upstream and downstream of VFMJ11_0098

  • Join these fragments by overlap extension PCR, creating a deletion construct

  • Clone the construct into a suicide vector (e.g., pKV363 or pEVS79) containing counterselectable markers

  • Introduce the vector into V. fischeri via conjugation or electroporation

  • Select for single crossover integrants using antibiotic selection

  • Counter-select for double crossover events using sucrose sensitivity (if using sacB)

  • Verify deletion by PCR and sequencing

  b) CRISPR-Cas9 approach:

  • Design sgRNA targeting VFMJ11_0098

  • Clone sgRNA into a CRISPR-Cas9 vector adapted for V. fischeri

  • Co-transform with a repair template containing flanking homology regions

  • Select transformants and verify editing by sequencing

• Knockdown approach:

  a) Antisense RNA method:

  • Design antisense RNA complementary to VFMJ11_0098 mRNA

  • Clone into an inducible expression vector for V. fischeri

  • Transform into wild-type V. fischeri

  • Induce expression and verify knockdown by qRT-PCR and Western blot

  b) CRISPRi approach:

  • Design sgRNA targeting the promoter region of VFMJ11_0098

  • Co-express with catalytically inactive Cas9 (dCas9)

  • Verify transcriptional repression by qRT-PCR

• Complementation system:

  • Clone wild-type VFMJ11_0098 into a V. fischeri expression vector

  • Transform into the knockout strain

  • Verify expression by qRT-PCR and Western blot

Each approach has advantages and limitations that should be considered based on the specific research questions and experimental design. The knockout approach provides complete elimination of gene function, while knockdown approaches allow for controlled and potentially reversible reduction in gene expression .

What approaches can be used to study the topology of VFMJ11_0098 in the bacterial membrane?

Several experimental approaches can be employed to study the topology of VFMJ11_0098 in the bacterial membrane:

• Reporter fusion methods:

  • PhoA (alkaline phosphatase) fusions: Active in periplasm, inactive in cytoplasm

  • GFP fusions: Fluorescent in cytoplasm, non-fluorescent in periplasm

  • LacZ (β-galactosidase) fusions: Active in cytoplasm, inactive in periplasm

  • Create systematic fusion libraries at different positions throughout VFMJ11_0098

  • Analyze activity patterns to map cytoplasmic versus periplasmic regions

• Cysteine scanning mutagenesis:

  • Introduce cysteine residues at strategic positions throughout the protein

  • Treat intact cells with membrane-impermeable sulfhydryl reagents

  • Detect modified cysteines using mass spectrometry or specific labeling

  • Cysteines accessible to external reagents indicate periplasmic/extracellular domains

• Protease accessibility:

  • Treat intact cells, spheroplasts, or membrane vesicles with proteases

  • Identify protected versus digested regions by mass spectrometry

  • Compare digestion patterns to determine membrane-spanning regions

• Epitope insertion and antibody accessibility:

  • Insert small epitope tags (FLAG, HA, c-Myc) at various positions

  • Assess antibody accessibility in intact cells versus permeabilized cells

  • Accessible epitopes in intact cells indicate extracellular/periplasmic localization

• Cryo-electron microscopy:

  • Purify protein in native membrane environment or reconstitute into nanodiscs

  • Perform cryo-EM analysis to determine structural organization in the membrane

  • Combine with computational modeling to generate complete topology map

The data from these complementary approaches can be integrated to create a comprehensive topology model of VFMJ11_0098, identifying cytoplasmic loops, transmembrane domains, and periplasmic regions. This topological information is crucial for understanding the protein's function and its potential interactions with other cellular components or host factors .

How can I assess the impact of point mutations in VFMJ11_0098 on Vibrio fischeri colonization?

Assessing the impact of point mutations in VFMJ11_0098 on Vibrio fischeri colonization requires a systematic approach combining molecular genetics, functional assays, and host colonization studies:

• Strategic mutation design:

  • Identify conserved residues through multiple sequence alignment of homologs

  • Target predicted functional domains or membrane-spanning regions

  • Focus on charged residues, potential catalytic sites, or conserved motifs

  • Design alanine substitutions or conservative/non-conservative replacements

• Mutation introduction methods:

  • Site-directed mutagenesis using overlap extension PCR

  • QuikChange mutagenesis of cloned VFMJ11_0098

  • CRISPR-Cas9 base editing for specific nucleotide changes

• Functional characterization:

  • Express mutant proteins in E. coli for in vitro studies

  • Assess protein stability and membrane localization

  • Analyze impacts on outer membrane vesicle production

  • Measure effects on membrane integrity and permeability

• Colonization experiments using Euprymna scolopes:

  • Generate V. fischeri strains carrying mutant versions of VFMJ11_0098

  • Assess initial colonization efficiency at 12-24 hours post-inoculation

  • Measure persistence in light organ over extended periods (1-4 weeks)

  • Quantify competitive fitness against wild-type strain in co-colonization assays

• Host response assessment:

  • Monitor hemocyte trafficking as an indicator of host immune response

  • Assess morphogenic changes in light organ development

  • Measure bioluminescence as a functional readout of successful colonization

• Experimental design considerations:

  • Use multiple juvenile squid per condition (n ≥ 15)

  • Include wild-type and knockout controls in each experiment

  • Perform biological replicates with different squid cohorts

  • Conduct blinded assessments where possible to reduce bias

This approach combines precision molecular techniques with true experimental design principles to establish causal relationships between specific amino acid residues in VFMJ11_0098 and colonization phenotypes. The results would provide insights into the functional domains critical for the protein's role in host-microbe interactions .

How does VFMJ11_0098 compare structurally and functionally to homologous proteins in other Vibrio species?

The structural and functional comparison of VFMJ11_0098 to homologous proteins in other Vibrio species reveals both conserved features and species-specific adaptations:

This comparative analysis provides a framework for understanding how VFMJ11_0098 may contribute to the unique symbiotic lifestyle of V. fischeri while sharing core functional properties with homologs in other Vibrio species. The specific amino acid sequence (MEDKIKHKLRIGWSYLLFLKQRVIHDRLTVSAGYMAYITLLSLVPLITVLLSVLSQFPVF...) contains both conserved elements critical for basic membrane protein function and specialized regions that may mediate V. fischeri-specific interactions .

What are the challenges in crystallizing membrane proteins like VFMJ11_0098 for structural studies?

Crystallizing membrane proteins like VFMJ11_0098 presents several significant challenges that must be addressed through specialized approaches:

• Protein extraction and stability issues:

  • Maintaining protein stability during solubilization from native membrane environment

  • Selecting appropriate detergents that maintain native fold without disrupting crystal contacts

  • Preventing protein aggregation during concentration steps

  • Optimizing buffer conditions to maintain stability over extended crystallization periods

• Technical crystallization challenges:

  • Limited hydrophilic surface area for forming crystal contacts

  • Detergent micelles surrounding the hydrophobic regions interfere with crystal packing

  • Phase separation during crystallization setup

  • Requirement for specialized crystallization screens designed for membrane proteins

• Alternative approaches to traditional crystallography:

  Approach	Advantages	Limitations	Applicability to VFMJ11_0098
  Lipidic cubic phase	Provides membrane-like environment	Technically challenging setup	Suitable for multi-spanning membrane proteins
  Bicelle crystallization	Combines lipid bilayer with detergent	Limited stability	Good for proteins sensitive to detergent
  Antibody fragment co-crystallization	Increases hydrophilic surface area	Requires antibody development	Could stabilize flexible regions
  Cryo-electron microscopy	Avoids crystallization entirely	Resolution limitations	Increasingly viable alternative

• Protein engineering strategies:

  • Truncation of flexible termini or loops

  • Introduction of stabilizing mutations

  • Fusion to crystallization chaperones (e.g., T4 lysozyme)

  • Surface entropy reduction to promote crystal contacts

• Expression and purification considerations:

  • Optimization of expression systems beyond standard E. coli

  • Screening multiple purification tags and their positions

  • Monodispersity assessment via size-exclusion chromatography

  • Thermal stability screening to identify stabilizing conditions

Due to these challenges, obtaining high-resolution structural information for VFMJ11_0098 would likely require a multi-faceted approach combining various crystallization techniques, protein engineering strategies, and possibly complementary structural methods such as cryo-EM or NMR spectroscopy for specific domains .

What are the best methods for detecting protein-protein interactions involving VFMJ11_0098?

Detecting protein-protein interactions involving membrane proteins like VFMJ11_0098 requires specialized approaches that accommodate the hydrophobic nature and membrane environment of these proteins:

• In vivo interaction methods:

  a) Bacterial two-hybrid systems:

  • BACTH (Bacterial Adenylate Cyclase Two-Hybrid) system specifically adapted for membrane proteins

  • Split-ubiquitin system modified for bacterial use

  • Advantages: Detects interactions in a membrane environment; relatively simple setup

  • Limitations: Potential false positives; requires efficient expression in host strain

  b) Förster Resonance Energy Transfer (FRET):

  • Fusion of VFMJ11_0098 and potential partners to fluorescent proteins

  • Measurement of energy transfer indicating proximity (<10 nm)

  • Advantages: Can detect interactions in native cellular context; provides spatial information

  • Limitations: Requires optimization of fusion constructs; potential interference from fluorescent tags

• In vitro interaction methods:

  a) Co-immunoprecipitation with membrane-specific modifications:

  • Crosslinking prior to solubilization to capture transient interactions

  • Optimization of detergent conditions to maintain interactions

  • Advantages: Can identify novel interaction partners; relatively straightforward

  • Limitations: May not preserve weak interactions; background binding issues

  b) Surface Plasmon Resonance (SPR) or Bio-Layer Interferometry (BLI):

  • Immobilization of purified VFMJ11_0098 in lipid nanodiscs or detergent

  • Real-time monitoring of binding to potential partners

  • Advantages: Provides kinetic and affinity data; highly sensitive

  • Limitations: Requires purified components; potential surface artifacts

• Mass spectrometry-based approaches:

  a) Proximity-dependent biotinylation (BioID or TurboID):

  • Fusion of biotin ligase to VFMJ11_0098

  • Identification of proximal proteins via streptavidin pulldown and MS

  • Advantages: Labels proteins in native environment; doesn't require stable interactions

  • Limitations: Identifies proximity not necessarily direct interaction; background labeling

  b) Crosslinking Mass Spectrometry (XL-MS):

  • Chemical crosslinking of VFMJ11_0098 complexes in membranes

  • MS identification of crosslinked peptides

  • Advantages: Provides structural constraints; can detect transient interactions

  • Limitations: Complex data analysis; crosslinker accessibility issues

For VFMJ11_0098, a combination of complementary approaches would be recommended, beginning with in vivo screening methods to identify potential interaction partners, followed by targeted in vitro techniques to validate and characterize specific interactions of interest. This multi-technique approach helps overcome the limitations of individual methods and provides more robust evidence for true biological interactions .

How can I optimize recombinant expression of VFMJ11_0098 to improve yield and solubility?

Optimizing recombinant expression of VFMJ11_0098 to improve yield and solubility requires a systematic approach addressing multiple factors:

• Expression system optimization:

  Parameter	Options to Test	Rationale
  E. coli strain	C41(DE3), C43(DE3), Lemo21(DE3)	Strains specifically engineered for membrane protein expression
  Expression vector	pET, pBAD, pMAL	Different promoter strengths and regulation mechanisms
  Fusion tags	His, MBP, SUMO, Mistic	Solubility enhancement and purification facilitation
  Codon optimization	Optimize for E. coli usage	Address potential rare codon issues in the V. fischeri sequence

• Expression condition optimization:

  • Reduced temperature (16-25°C) to slow protein production and improve folding

  • Lower inducer concentration (0.01-0.1 mM IPTG) to prevent inclusion body formation

  • Extended expression time (24-48 hours) at lower temperatures

  • Addition of chemical chaperones (glycerol, sorbitol) to the growth medium

  • Osmotic stress induction (sucrose, salt) to upregulate chaperone systems

• Membrane extraction and solubilization:

  • Screening multiple detergents for solubilization efficiency:

    • Mild detergents: DDM, LMNG, digitonin

    • Zwitterionic detergents: LDAO, FC-12

    • Detergent mixtures and novel amphipols

  • Optimizing detergent:protein ratios to prevent aggregation

  • Addition of lipids during solubilization to stabilize native structure

  • Stepwise extraction protocols to improve selectivity

• Protein stabilization strategies:

  • Addition of specific lipids (E. coli total lipid extract, specific phospholipids)

  • Inclusion of cholesterol hemisuccinate (CHS) as a stabilizing agent

  • Buffer optimization (pH, salt concentration, specific ions)

  • Addition of ligands or substrates if known

• Alternative expression approaches:

  • Cell-free expression systems with direct incorporation into nanodiscs or liposomes

  • Yeast expression systems (Pichia pastoris) for eukaryotic processing machinery

  • Expression of individual domains if full-length protein proves challenging

For VFMJ11_0098, initial trials should focus on specialized E. coli strains like C41(DE3) with reduced temperature expression (20°C) using mild induction conditions. The full-length protein (310 amino acids) should be expressed with a removable tag system, and multiple detergents should be screened in parallel for optimal solubilization. Each optimization step should be assessed by SDS-PAGE, Western blotting, and size-exclusion chromatography to evaluate yield, purity, and monodispersity .

How can I quantify VFMJ11_0098 expression levels under different environmental conditions?

Quantifying VFMJ11_0098 expression levels under different environmental conditions requires a combination of molecular and biochemical techniques:

• Transcript-level quantification:

  a) Quantitative reverse transcription PCR (qRT-PCR):

  • Design primers specific to VFMJ11_0098 mRNA

  • Extract total RNA from V. fischeri under various conditions

  • Convert to cDNA and perform qPCR

  • Normalize to stable reference genes (rpoD, recA, or gyrB)

  b) RNA-Seq analysis:

  • Perform transcriptome-wide sequencing under different conditions

  • Map reads to VFMJ11_0098 locus

  • Calculate normalized expression values (FPKM/TPM)

  • Identify co-regulated genes for pathway analysis

• Protein-level quantification:

  a) Western blotting:

  • Generate specific antibodies against VFMJ11_0098 or use His-tag antibodies

  • Extract membrane fractions from V. fischeri cells

  • Quantify band intensity relative to loading controls

  b) Mass spectrometry-based quantification:

  • Label-free quantification of membrane-enriched fractions

  • SILAC or TMT labeling for comparative proteomics

  • Parallel reaction monitoring (PRM) for targeted quantification

  • Use of synthetic peptide standards for absolute quantification

• In situ visualization:

  a) Fluorescent protein fusions:

  • Create chromosomal VFMJ11_0098-GFP/mCherry fusion

  • Measure fluorescence under different conditions

  • Provides both expression level and localization data

  b) Immunofluorescence microscopy:

  • Fix cells from different conditions

  • Probe with anti-VFMJ11_0098 antibodies

  • Quantify signal intensity across population

• Experimental conditions to test:

  Environmental Factor	Range to Test	Relevance
  Temperature	15-30°C	Mimics host and seawater temperatures
  Salinity	20-40 g/L NaCl	Represents different marine environments
  Oxygen levels	Aerobic to microaerobic	Conditions in squid light organ vs. seawater
  Host factors	Squid tissue extracts	Simulate host environment
  Cell density	Early log to stationary	Quorum sensing effects
  Biofilm vs. planktonic	Growth on surfaces vs. liquid	Different growth modes

• Data analysis and integration:

  • Correlation of transcript and protein-level changes

  • Time-course analysis to capture expression dynamics

  • Multivariate analysis to identify key regulatory conditions

  • Integration with known regulatory networks in V. fischeri