Recombinant Shewanella sp. UPF0761 membrane protein Shewana3_0311 (Shewana3_0311)

What is the structural classification of Shewana3_0311 membrane protein?

Shewana3_0311 is classified as a UPF0761 (Uncharacterized Protein Family 0761) membrane protein found in Shewanella sp. strain ANA-3. The protein consists of 337 amino acids and has been computationally modeled using AlphaFold (AF-A0KRY5-F1) with a global pLDDT (predicted Local Distance Difference Test) confidence score of 75.55, indicating a reasonably confident structural prediction . The protein is predicted to have multiple transmembrane domains, consistent with its classification as a membrane protein. The model demonstrates regions of varying confidence, with some segments showing high confidence scores (pLDDT > 90) while others display moderate confidence (70 < pLDDT ≤ 90) .

How does Shewana3_0311 compare to similar proteins in other Shewanella species?

Comparative analysis reveals significant sequence similarity between Shewana3_0311 and homologous UPF0761 membrane proteins from other Shewanella species. The table below highlights key comparisons:

The high sequence similarity suggests conserved function across Shewanella species, while the differences in C-terminal regions may indicate species-specific adaptations or regulatory mechanisms . Researchers working with Shewana3_0311 should consider these homologs when designing experiments to investigate evolutionary conservation of structure-function relationships.

What are the optimal storage and handling conditions for recombinant Shewana3_0311 protein?

For optimal stability and activity of recombinant Shewana3_0311 protein, the following storage and handling protocols are recommended:

• Storage temperature: Store at -20°C for regular use, or at -80°C for extended long-term storage .

• Buffer composition: The protein is most stable in Tris-based buffer containing 50% glycerol, specifically optimized for membrane proteins .

• Freeze-thaw considerations: Repeated freezing and thawing significantly reduces protein stability and should be strictly avoided. Instead, prepare small working aliquots before freezing .

• Working aliquots: Store working aliquots at 4°C for up to one week to minimize freeze-thaw cycles while maintaining activity .

• Protein concentration: Maintaining appropriate concentration is critical; dilution below 0.1 mg/mL may accelerate degradation due to increased surface interaction with the storage vessel.

These storage recommendations are consistent across recombinant UPF0761 membrane proteins from different Shewanella species, suggesting conserved structural properties that affect stability .

What expression systems are most effective for producing recombinant Shewana3_0311?

For optimal expression of functional recombinant Shewana3_0311, E. coli-based expression systems have proven most effective . When developing an expression strategy, researchers should consider:

• Host selection: E. coli is the documented host for successful expression of recombinant Shewana3_0311 . Specialized strains designed for membrane protein expression (such as C41(DE3) or C43(DE3)) may yield better results than standard BL21(DE3) strains.

• Vector design: Vectors containing T7 promoters with His-tag fusion capability have been successfully employed . The positioning of the His-tag (N-terminal versus C-terminal) should be evaluated experimentally as it may affect protein folding and function.

• Induction conditions: Membrane proteins often require gentler induction conditions. Consider:

  • Lower IPTG concentrations (0.1-0.5 mM rather than standard 1 mM)

  • Reduced induction temperature (16-25°C rather than 37°C)

  • Extended induction periods (overnight rather than 3-4 hours)

• Solubilization strategies: As a membrane protein, Shewana3_0311 requires appropriate detergents for extraction from cellular membranes. Common effective detergents include n-dodecyl-β-D-maltoside (DDM), n-octyl-β-D-glucoside (OG), or digitonin.

• Purification approach: Immobilized metal affinity chromatography (IMAC) using the His-tag is effective for initial purification, followed by size-exclusion chromatography for higher purity preparations.

When transitioning to functional studies, researchers should verify the proper folding and membrane insertion of the recombinant protein through circular dichroism or limited proteolysis experiments.

How can I verify the structural integrity of purified Shewana3_0311?

Verifying the structural integrity of purified Shewana3_0311 is critical for ensuring reliable experimental outcomes. A multi-faceted approach is recommended:

• Computational structure validation: Compare experimental data with the AlphaFold model (AF-A0KRY5-F1, pLDDT: 75.55) to assess structural concordance . Focus particularly on regions with high confidence scores (pLDDT > 90) as reference points.

• Circular dichroism (CD) spectroscopy: This technique provides information about secondary structure content. For membrane proteins like Shewana3_0311, expect CD spectra characteristic of α-helical structures, with negative peaks at 208 nm and 222 nm.

• Thermal shift assays: Monitor protein unfolding as a function of temperature to assess stability. Membrane proteins typically exhibit complex denaturation profiles due to their interaction with detergents.

• Size-exclusion chromatography with multi-angle light scattering (SEC-MALS): This technique helps determine whether the protein exists in a monomeric state or forms higher-order oligomers in solution, which can be critical for understanding functional states.

• Limited proteolysis: Properly folded membrane proteins often show characteristic resistance patterns to protease digestion. Unexpected digestion patterns may indicate misfolding or structural perturbations.

• Microscale thermophoresis (MST) or isothermal titration calorimetry (ITC): These techniques can assess whether the purified protein maintains expected ligand-binding properties, if any binding partners are known.

Each method provides complementary information about different aspects of protein structure, and concordance across multiple techniques provides the strongest evidence for structural integrity.

What is currently known about the biological function of Shewana3_0311?

• Membrane localization: As a predicted membrane protein with multiple transmembrane domains, Shewana3_0311 likely functions in membrane-associated processes such as transport, signaling, or maintaining membrane integrity .

• Taxonomic context: Shewanella species are facultatively anaerobic gram-negative bacteria primarily found in marine environments, often in extreme conditions (low temperature, high pressure) . Membrane proteins in these organisms frequently participate in environmental adaptation.

• Comparative genomics: The conservation of UPF0761 membrane proteins across multiple Shewanella species suggests an important functional role . The high sequence similarity between homologs points to conserved functions, while differences in C-terminal regions may indicate species-specific adaptations.

• Bacterial physiology context: Shewanella species are known for their versatile respiratory capabilities, including the ability to use diverse electron acceptors under anaerobic conditions . Membrane proteins often play crucial roles in respiratory chains and electron transport systems.

• Virulence associations: Some Shewanella membrane proteins contribute to pathogenicity. While specific virulence associations for Shewana3_0311 are not documented, researchers should consider this potential role, especially since Shewanella infections have been reported in clinical settings .

Future research directions might include gene knockout studies to observe phenotypic effects, protein-protein interaction studies to identify binding partners, or comparative physiological studies across species expressing homologous proteins.

How can researchers investigate potential protein-protein interactions involving Shewana3_0311?

Investigating protein-protein interactions (PPIs) involving Shewana3_0311 requires specialized approaches appropriate for membrane proteins. A systematic research strategy might include:

• Bacterial two-hybrid (B2H) systems: Traditional yeast two-hybrid systems are often unsuitable for membrane proteins. B2H systems have been optimized for membrane protein interactions and can serve as an initial screening method.

• Co-immunoprecipitation (Co-IP) with specific adaptations:

  • Use cross-linking agents to stabilize transient interactions

  • Employ gentle detergents (DDM, digitonin) that maintain native membrane protein complexes

  • Consider on-membrane Co-IP approaches that preserve the lipid environment

• Proximity-based labeling techniques:

  • BioID or TurboID fusion constructs can identify proteins in close proximity to Shewana3_0311 in vivo

  • This approach is particularly valuable for membrane proteins as it captures interactions in their native cellular context

• Quantitative proteomic approaches:

  • SILAC (Stable Isotope Labeling with Amino acids in Cell culture) combined with pull-down experiments

  • Label-free quantitative proteomics comparing wild-type vs. knockout strains

• Surface plasmon resonance (SPR) or biolayer interferometry (BLI):

  • For validating specific interactions identified through screening approaches

  • Requires reconstitution of Shewana3_0311 in appropriate membrane-mimetic environments (nanodiscs, liposomes)

• In silico prediction combined with experimental validation:

  • Utilize computational tools like PIPE (Protein-Protein Interaction Prediction Engine) or SPRING (Studying Protein-protein Interaction Networks in Genomics)

  • Cross-reference predictions with experimental data from related Shewanella membrane proteins

When designing PPI experiments, consider that membrane proteins often form interactions within the membrane plane (with other membrane proteins) and also with soluble proteins at their cytoplasmic or periplasmic domains. Experimental designs should account for both types of potential interactions.

What approaches can be used to study the role of Shewana3_0311 in bacterial membrane dynamics?

Investigating the role of Shewana3_0311 in bacterial membrane dynamics requires specialized techniques that preserve membrane integrity while providing meaningful functional data. A comprehensive experimental approach might include:

• Fluorescence microscopy with protein tagging:

  • Fuse Shewana3_0311 with fluorescent proteins (GFP variants optimized for bacterial expression)

  • Track protein localization during different growth phases and environmental conditions

  • Use FRAP (Fluorescence Recovery After Photobleaching) to assess membrane mobility

• Lipidomic analysis in knockout strains:

  • Generate Shewana3_0311 knockout mutants using CRISPR-Cas9 or homologous recombination

  • Compare membrane lipid composition between wild-type and mutant strains using LC-MS/MS

  • Analyze changes in phospholipid species, fatty acid composition, and membrane fluidity

• Membrane biophysical properties assessment:

  • Measure membrane fluidity using fluorescent probes (DPH, Laurdan)

  • Assess membrane potential with voltage-sensitive dyes

  • Determine membrane permeability through solute leakage assays

• Electron microscopy techniques:

  • Cryo-electron microscopy to visualize membrane ultrastructure

  • Immunogold labeling to localize Shewana3_0311 within the membrane

  • Correlative light and electron microscopy (CLEM) to link functional states with structural features

• Reconstitution in model membrane systems:

  • Incorporate purified Shewana3_0311 into liposomes or nanodiscs

  • Measure effects on membrane curvature, lipid domain formation, or membrane fusion events

  • Assess ion or small molecule permeability changes

• Phenotypic analysis under environmental stress:

  • Compare wild-type and knockout strains under conditions relevant to Shewanella ecology:

    • Osmotic stress (varying salinity)

    • Temperature fluctuations

    • Anaerobic transitions

    • Presence of heavy metals or other environmental contaminants

These approaches should be integrated with the understanding that Shewanella species inhabit extreme aquatic environments , and membrane proteins likely play crucial roles in adaptation to these conditions.

How does the structure of Shewana3_0311 compare to UPF0761 proteins from other bacterial species?

Structural comparison of Shewana3_0311 with UPF0761 membrane proteins from other bacterial species reveals important evolutionary relationships and potential functional implications:

• Intra-genus comparison: Within the Shewanella genus, UPF0761 proteins show high structural conservation. Comparative analysis of AlphaFold predictions for Shewana3_0311 (A0KRY5) with homologs from S. baltica (A9KXA4) and S. pealeana (A8H9I2) reveals:

  • Conserved transmembrane topology with similar helix arrangements

  • Nearly identical core structural elements

  • Variable loop regions, particularly at the C-terminus

  • pLDDT confidence scores in similar ranges (70-80), suggesting comparable modeling reliability

• Transmembrane topology patterns: All examined UPF0761 proteins share a consistent predicted membrane topology featuring:

  • Multiple transmembrane spanning helices

  • Short connecting loops

  • Characteristic N-terminal and C-terminal domains likely exposed to different sides of the membrane

• Evolutionary structural conservation: The degree of structural conservation exceeds what would be expected based on sequence identity alone, suggesting evolutionary pressure to maintain specific three-dimensional arrangements crucial for function.

• Structural motifs of functional significance: Detailed examination reveals conserved structural motifs that may indicate functional sites:

  • Charged residue clusters in transmembrane regions that might facilitate ion transport

  • Conserved glycine residues that could serve as flexibility points within helices

  • Aromatic residue patterns that might be involved in substrate recognition or protein-protein interactions

• Variable regions of potential functional divergence: Areas showing higher structural variability between homologs may represent regions adapted for species-specific functions or interactions.

This structural comparison provides a foundation for targeted experimental investigations into functional conservation and divergence across bacterial species.

What experimental approaches can reveal evolutionary conservation of function in UPF0761 membrane proteins?

Investigating the evolutionary conservation of function in UPF0761 membrane proteins requires integrating multiple experimental approaches that can reveal both structural and functional relationships. A comprehensive research strategy might include:

• Complementation studies across species:

  • Generate knockout mutants for Shewana3_0311 in Shewanella sp. ANA-3

  • Attempt functional complementation with homologous genes from S. baltica, S. pealeana, and more distantly related bacteria

  • Quantify the degree of functional rescue to assess conservation of core functions

• Domain swapping experiments:

  • Create chimeric proteins by exchanging domains between Shewana3_0311 and homologs

  • Express in appropriate knockout backgrounds

  • Map functional domains through systematic analysis of which chimeras retain activity

• Site-directed mutagenesis of conserved residues:

  • Identify strictly conserved amino acids across UPF0761 homologs

  • Generate point mutations and assess impact on protein function

  • Determine whether equivalent mutations in different homologs produce similar phenotypes

• Heterologous expression studies:

  • Express Shewana3_0311 and homologs in model organisms (E. coli, B. subtilis)

  • Compare phenotypic effects to identify conserved functional pathways

  • Use transcriptomic and proteomic analyses to map affected cellular processes

• Evolutionary rate analysis:

  • Calculate evolutionary rates (dN/dS ratios) for different protein regions

  • Identify portions under strong purifying selection (conserved function) versus diversifying selection

  • Correlate evolutionary constraints with structural features from AlphaFold models

• Ancestral sequence reconstruction:

  • Computationally predict ancestral UPF0761 protein sequences

  • Express and characterize these reconstructed proteins

  • Track functional shifts that occurred during evolution of the protein family

These approaches collectively can reveal the extent to which function is conserved across UPF0761 proteins and identify key structural determinants of these functions. Results from these studies will contribute to understanding the broader evolutionary history and functional diversity of this protein family.

What are the most effective approaches for studying Shewana3_0311 in the context of bacterial stress response?

Investigating Shewana3_0311's potential role in bacterial stress response requires methodologies that can detect dynamic changes in protein function, expression, and interaction networks under various stress conditions. A comprehensive research strategy might include:

• Expression profiling under stress conditions:

  • Quantitative RT-PCR to measure Shewana3_0311 transcript levels under stresses relevant to Shewanella ecology:

    • Osmotic stress (varying salinity levels)

    • Temperature shifts (cold shock, heat shock)

    • Oxygen limitation

    • Heavy metal exposure

    • pH variations

  • RNA-seq for genome-wide expression context, comparing wild-type and knockout strains

  • Proteomics to confirm translation of transcriptional changes

• Promoter activity analysis:

  • Clone the Shewana3_0311 promoter region upstream of reporter genes (gfp, lacZ)

  • Monitor promoter activity in real-time during stress exposure

  • Identify transcription factors controlling stress-responsive expression through DNA-protein interaction studies

• Protein modification and turnover:

  • Pulse-chase experiments to measure protein stability under stress

  • Phosphoproteomics to detect stress-induced post-translational modifications

  • Targeted mutagenesis of potential regulatory sites

• Membrane physiology assessment:

  • Measure membrane fluidity changes using fluorescent probes under stress conditions

  • Compare wild-type and Shewana3_0311 knockout strains for differences in:

    • Membrane permeability

    • Proton gradient maintenance

    • Ion homeostasis

    • Membrane potential

• In situ protein dynamics:

  • Single-molecule tracking to monitor protein mobility and clustering during stress

  • FRET-based sensors to detect conformational changes under stress conditions

  • Crosslinking studies to capture stress-specific protein-protein interactions

• Systems biology approaches:

  • Integrate transcriptomic, proteomic, and metabolomic data

  • Construct network models of stress response pathways

  • Position Shewana3_0311 within these networks based on experimental evidence

When designing these experiments, researchers should consider that Shewanella species occupy extreme environments and may possess unique stress response mechanisms adapted to these niches. The experimental stress conditions should therefore mimic relevant ecological challenges faced by these bacteria.

How can cryo-electron microscopy be optimized for structural studies of Shewana3_0311?

Optimizing cryo-electron microscopy (cryo-EM) for structural studies of Shewana3_0311 requires addressing specific challenges associated with membrane proteins while leveraging recent methodological advances. A detailed strategy might include:

• Sample preparation optimization:

  • Detergent selection: Screen multiple detergents (DDM, LMNG, GDN) and detergent concentrations to identify conditions that maintain native structure while minimizing background in images

  • Reconstitution approaches:

    • Nanodiscs with MSP1D1 or MSP1E3D1 scaffold proteins

    • Amphipols (A8-35, PMAL-C8)

    • Saposin-based lipid nanoparticles (Salipro)

  • Lipid composition: Incorporate native Shewanella lipids extracted from bacterial membranes to better mimic the native environment

• Grid preparation techniques:

  • Surface treatment: Evaluate glow discharge parameters, nanogold coating, or graphene coating to optimize protein orientation and distribution

  • Vitrification conditions: Test different blotting times and temperatures to achieve optimal ice thickness

  • Sample concentration gradient: Prepare grids with varying protein concentrations (0.5-5 mg/mL) to maximize particles per image while avoiding aggregation

• Data collection strategy:

  • Motion correction optimization: Collect movies with 40-60 frames to allow for dose-weighted motion correction

  • Defocus range: Collect data across a wide defocus range (-0.8 to -2.5 μm) to ensure complete CTF coverage

  • Tilting strategy: Consider collecting data at multiple stage tilts (0°, 20°, 40°) to address preferred orientation issues common with membrane proteins

• Image processing considerations:

  • 2D classification: Perform extensive 2D classification to identify different protein orientations and conformational states

  • 3D classification: Use 3D classification without alignment to separate conformational heterogeneity

  • Mask optimization: Develop protein-specific masks that focus refinement on the protein while excluding detergent or nanodisc components

• Validation and resolution enhancement:

  • Cross-validation: Split data processing into two independent half-sets from the beginning

  • Local resolution estimation: Map local resolution variations to identify well-resolved and flexible regions

  • Model building: Integrate the AlphaFold prediction (AF-A0KRY5-F1) as a starting model for refinement against cryo-EM density

This optimized approach acknowledges that membrane proteins like Shewana3_0311 present special challenges for cryo-EM, including preferred orientation, conformational heterogeneity, and signal-to-noise challenges from detergent or lipid components.

What is the recommended protocol for site-directed mutagenesis of conserved residues in Shewana3_0311?

The following protocol outlines a comprehensive approach for site-directed mutagenesis of conserved residues in Shewana3_0311, incorporating steps to address the specific challenges of working with membrane proteins:

• Target residue identification:

  • Perform multiple sequence alignment of UPF0761 family proteins across diverse Shewanella species

  • Identify strictly conserved residues using ConSurf or similar conservation analysis tools

  • Prioritize residues based on:

    • Location in predicted functional domains

    • Predicted accessibility in the membrane

    • Presence in conserved sequence motifs

    • Correlation with the AlphaFold structural model confidence scores

• Primer design considerations:

  • Design mutagenic primers with the following parameters:

    • 25-35 nucleotides in length

    • Mutation site positioned centrally

    • Terminal G/C content of 40-60%

    • Melting temperature (Tm) of 78-82°C (calculated using modified formula for mutagenic primers)

    • Avoid secondary structure formation

  • For transmembrane regions, consider codon optimization that respects the codon usage bias of Shewanella

• PCR-based mutagenesis procedure:

  • Use a high-fidelity DNA polymerase with proofreading activity (Q5, Pfu Ultra)

  • Template: plasmid containing Shewana3_0311 gene with appropriate tags for detection/purification

  • Thermal cycling parameters:

    • Initial denaturation: 98°C for 30 seconds

    • 16-18 cycles of: 98°C for 10 seconds, 55-65°C for 20 seconds, 72°C for 30 seconds/kb

    • Final extension: 72°C for 5 minutes

  • DpnI digestion: 1 hour at 37°C to eliminate template DNA

• Transformation and screening:

  • Transform into high-efficiency competent cells (efficiency ≥10^8 CFU/μg)

  • Plate on selective media appropriate for the vector

  • Screen 4-6 colonies by colony PCR and sequencing

  • Verify the entire Shewana3_0311 coding sequence to confirm only the intended mutation is present

• Expression and functional verification:

  • Express wild-type and mutant proteins in parallel under identical conditions

  • Verify expression levels by Western blot

  • Compare membrane localization patterns

  • Assess proper folding through limited proteolysis or thermal shift assays

  • Conduct functional assays appropriate to the predicted role of the mutated residue

• Data analysis and interpretation:

  • Classify mutations based on phenotypic effects:

    • Silent mutations (no detectable effect)

    • Hypomorphic mutations (reduced function)

    • Hypermorphic mutations (enhanced function)

    • Neomorphic mutations (altered function)

    • Amorphic mutations (loss of function)

  • Map mutations onto the structural model to identify functional domains

This protocol enables systematic characterization of structure-function relationships in Shewana3_0311 and contributes to understanding the broader functional significance of conserved residues in UPF0761 family proteins.

How should researchers design experiments to investigate potential transport functions of Shewana3_0311?

Investigating whether Shewana3_0311 functions as a transporter requires a systematic experimental approach that combines genetic, biochemical, and biophysical methods. The following experimental design provides a comprehensive framework:

• Bioinformatic analysis and hypothesis generation:

  • Conduct detailed sequence and structure analysis using transporter-specific prediction tools (TCDB, TransportDB)

  • Identify conserved motifs associated with known transporter families

  • Generate testable hypotheses about potential substrates based on:

    • Genomic context (nearby genes)

    • Evolutionary relationships to characterized transporters

    • Structural features from the AlphaFold model

• In vivo transport assays:

  • Genetic system establishment:

    • Generate Shewana3_0311 knockout strains

    • Create complementation strains with wild-type and mutant variants

    • Develop inducible expression systems for controlled expression levels

  • Growth phenotype screening:

    • Test growth on media with different potential substrates as sole carbon/nitrogen/sulfur sources

    • Assess tolerance to toxic compounds (potential efflux substrates)

    • Measure growth under varying ion concentrations (if ion transport is suspected)

  • Radioactive or fluorescent substrate uptake:

    • Select 5-10 candidate substrates based on bioinformatic predictions

    • Measure uptake rates in wild-type vs. knockout strains

    • Calculate kinetic parameters (Km, Vmax) for validated substrates

• Reconstitution in artificial membrane systems:

  • Liposome reconstitution:

    • Purify Shewana3_0311 using optimized detergents

    • Reconstitute into liposomes with controlled lipid composition

    • Incorporate pH or voltage-sensitive dyes to monitor gradient formation

  • Transport measurements:

    • Design assays specific to the hypothesized transport mechanism:

      • For ion transport: measure ion flux using ion-selective electrodes

      • For substrate transport: quantify substrate accumulation inside liposomes

      • For channel activity: conduct electrophysiological measurements

  • Energetic coupling determination:

    • Test dependence on electrochemical gradients (ΔΨ, ΔpH)

    • Assess ATP requirements or other energy coupling mechanisms

    • Measure transport directionally (influx vs. efflux)

• Structure-function analysis:

  • Generate point mutations in predicted substrate-binding or translocation pathway residues

  • Measure transport activity of mutant proteins using established assays

  • Correlate functional changes with structural features

• Physiological relevance assessment:

  • Environmental condition testing:

    • Measure transport activity under conditions relevant to Shewanella ecology:

      • Varying salinity

      • Different temperatures

      • Aerobic vs. anaerobic conditions

  • Competition assays:

    • Conduct mixed culture experiments with wild-type and knockout strains

    • Assess competitive fitness under different environmental conditions

This experimental framework provides a comprehensive approach to characterizing potential transport functions of Shewana3_0311, progressing from hypothesis generation to detailed mechanistic understanding and physiological relevance.