Recombinant Serpentine receptor class epsilon-31 (sre-31)

How is recombinant sre-31 typically produced for research applications?

Recombinant sre-31 is typically produced in E. coli expression systems using the full-length protein sequence (amino acids 1-357) . The protein is commonly fused to affinity tags, most frequently an N-terminal histidine (His) tag that facilitates purification through metal affinity chromatography . The production process involves:

• Cloning the sre-31 coding sequence into an appropriate expression vector

• Transforming the construct into E. coli

• Inducing protein expression under optimized conditions

• Cell lysis and extraction of the protein

• Purification using affinity chromatography

• Quality control through SDS-PAGE analysis to confirm purity (>90% is typically achieved)

• Lyophilization for long-term storage

The recombinant protein is supplied in lyophilized form, which enhances stability and extends shelf life . Researchers should note that while E. coli is the predominant expression system, it lacks the machinery for post-translational modifications that might be present in the native protein.

Storage Conditions:

The optimal storage conditions for recombinant sre-31 are:

• Store lyophilized powder at -20°C to -80°C upon receipt

• After reconstitution, aliquot the protein to avoid repeated freeze-thaw cycles

• Working aliquots can be stored at 4°C for up to one week

• For long-term storage after reconstitution, add glycerol to a final concentration of 50% and store at -20°C to -80°C

Reconstitution Protocol:

• Briefly centrifuge the vial prior to opening to bring contents to the bottom

• Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• For long-term storage, add glycerol to 5-50% final concentration

• If using for specific assays, reconstitute at 500 μg/mL in PBS or an appropriate buffer

The typical storage buffer consists of a Tris/PBS-based buffer with 6% Trehalose at pH 8.0 . Alternately, some preparations use a Tris-based buffer with 50% glycerol optimized for protein stability .

What quality control methods should be employed when working with recombinant sre-31?

When working with recombinant sre-31, researchers should implement the following quality control measures:

• Purity Assessment: Verify protein purity via SDS-PAGE. Commercial preparations typically guarantee >90% purity .

• Identity Confirmation:

  • Mass spectrometry to confirm the molecular weight and sequence

  • Western blotting with antibodies against sre-31 or the fusion tag

  • N-terminal sequencing for the first 5-10 amino acids

• Structural Integrity:

  • Circular dichroism (CD) spectroscopy to assess secondary structure

  • Fluorescence spectroscopy to evaluate tertiary structure

• Functional Analysis:

  • Binding assays with potential ligands

  • Reconstitution into artificial membrane systems to assess folding

• Endotoxin Testing:

  • LAL (Limulus Amebocyte Lysate) assay to ensure preparations are endotoxin-free

A comprehensive quality control workflow should include documentation of batch number, production date, and experimental results to ensure reproducibility across experiments.

How do serpentine receptors like sre-31 compare across different species?

Serpentine receptors, characterized by their seven-transmembrane domain architecture, are found across diverse organisms but show significant sequence divergence, making cross-species comparisons challenging . Based on comparative analyses:

• Functional Divergence: Despite structural similarities, serpentine receptors have evolved diverse functions across species, ranging from chemosensation in C. elegans to potential roles in host-parasite interactions in P. falciparum .

The identification of serpentine receptor-like proteins in diverse organisms like P. falciparum opens new perspectives for understanding essential aspects of parasite biology and host-pathogen interactions .

What are the challenges in expressing and purifying functional recombinant serpentine receptors?

Expressing and purifying functional serpentine receptors presents multiple challenges:

• Membrane Protein Expression Barriers:

  • Hydrophobic transmembrane domains often lead to protein aggregation or misfolding

  • Overexpression can overwhelm membrane insertion machinery in host cells

  • E. coli lacks machinery for eukaryotic post-translational modifications

• Solubilization and Stability Issues:

  • Maintaining native conformation during extraction from membranes is difficult

  • Detergent selection is critical - must efficiently solubilize without denaturing

  • Receptor stability outside the lipid bilayer environment is often compromised

• Purification Complications:

  • Low expression yields compared to soluble proteins

  • Purification in detergent micelles adds complexity

  • His-tagged proteins (like recombinant sre-31) may show non-specific binding

• Functional Assessment Difficulties:

  • Reconstitution into artificial membrane systems is required for functional studies

  • Native ligands for many serpentine receptors (including sre-31) remain unknown

  • Confirming proper folding and functional activity is challenging

• Specialized Solutions:

  • Using specialized expression systems (insect cells, mammalian cells)

  • Incorporating fusion partners to enhance solubility

  • Employing nanodiscs or proteoliposomes for functional reconstitution

  • Adding stabilizing agents like glycerol during storage

For sre-31 specifically, E. coli expression systems have been successfully utilized with His-tagging strategies , but researchers should consider that the functional properties of the recombinant protein may differ from those of the native receptor in C. elegans.

How can researchers functionally characterize recombinant sre-31?

Functional characterization of recombinant sre-31 requires multiple complementary approaches:

• Ligand-Binding Assays:

  • Direct binding assays using potentially radiolabeled or fluorescently-labeled ligands

  • Competition binding assays to determine binding affinity and specificity

  • Surface plasmon resonance (SPR) to measure real-time binding kinetics

• Reconstitution Systems:

  • Proteoliposomes containing purified recombinant sre-31

  • Nanodiscs for a more native-like membrane environment

  • Cell-based assays with heterologous expression in mammalian or insect cells

• Signaling Pathway Analysis:

  • G protein coupling assays (if sre-31 functions through G proteins)

  • Calcium mobilization assays

  • ERK/MAPK phosphorylation analysis

  • β-arrestin recruitment assays

• Structural Studies:

  • Circular dichroism to confirm secondary structure integrity

  • Limited proteolysis to probe conformational states

  • Cryo-electron microscopy for structural determination in detergent micelles or nanodiscs

• In vivo Validation in C. elegans:

  • Rescue experiments in sre-31 knockout worms

  • Phenotypic characterization of sre-31 mutants

  • Localization studies using fluorescently tagged sre-31

A comprehensive functional characterization workflow would involve initial in vitro binding and structural studies with the recombinant protein, followed by cellular assays and ultimately in vivo validation in C. elegans.

What computational approaches can predict sre-31 binding partners and function?

Several computational approaches can help predict sre-31 binding partners and function:

• Homology-Based Function Prediction:

  • Sequence alignment with functionally characterized serpentine receptors

  • Structural modeling based on crystallized GPCRs

  • Analysis of conserved motifs and domains

• Molecular Docking and Virtual Screening:

  • In silico screening of small molecule libraries against sre-31 structural models

  • Molecular dynamics simulations to identify stable binding interactions

  • Binding energy calculations to prioritize potential ligands

• Protein-Protein Interaction Predictions:

  • Network analysis using databases like STRING

  • Co-expression data analysis from C. elegans transcriptome studies

  • Prediction of G protein coupling specificity based on intracellular loop sequences

• Pathway and Context Analysis:

  • Gene ontology enrichment

  • Pathway mapping using KEGG or similar databases

  • Analysis of co-evolved gene families

• Machine Learning Approaches:

  • Training on known GPCR-ligand pairs to predict potential sre-31 ligands

  • Classification of sre-31 within receptor subfamilies

  • Prediction of post-translational modifications

The amino acid sequence (MIIKNTGTSTFIWLPVYFYNE...) provided in the search results can serve as input for these computational methods. Researchers should validate computational predictions with experimental approaches, as the accuracy of these methods varies significantly.

What are the critical experimental controls when working with recombinant sre-31 in binding studies?

When conducting binding studies with recombinant sre-31, researchers should implement the following critical controls:

• Negative Controls:

  • Heat-denatured sre-31 protein to confirm specificity

  • Irrelevant proteins with similar size/tag (e.g., His-tagged non-receptor protein)

  • Buffer-only conditions without receptor

  • Non-specific ligands structurally distinct from test compounds

• Positive Controls:

  • Known receptor-ligand pairs from related serpentine receptor families

  • Anti-tag antibodies to confirm protein presence and accessibility

  • Properly folded control membrane proteins with verified activity

• Specificity Controls:

  • Competitive binding with unlabeled ligands

  • Concentration-dependent binding curves

  • Binding to receptor mutants with altered binding sites

• Technical Validation:

  • Multiple protein preparation batches to confirm reproducibility

  • Different detection methods (fluorescence, radioligand, SPR)

  • Variation in experimental conditions (temperature, pH, ionic strength)

• Expression System Controls:

  • Empty vector-transformed E. coli extracts

  • Mock purifications from non-expressing cells

  • Comparison with membrane preparations from C. elegans (if available)

Documenting all control experiments in a standardized format is essential for result interpretation and reproducibility. Researchers should also consider that the His-tag used in recombinant sre-31 may influence binding properties and include appropriate tagged controls.

How can researchers utilize recombinant sre-31 in structural biology studies?

Structural biology studies of recombinant sre-31 require specialized approaches for membrane proteins:

• X-ray Crystallography:

  • Protein stabilization through fusion partners (e.g., T4 lysozyme)

  • Lipidic cubic phase crystallization

  • Detergent screening to identify conditions maintaining native structure

  • Co-crystallization with stabilizing antibodies or nanobodies

• Cryo-Electron Microscopy (Cryo-EM):

  • Vitrification of purified sre-31 in detergent micelles

  • Use of reconstituted nanodiscs to provide a lipid bilayer environment

  • Single-particle analysis for 3D reconstruction

  • Implementation of contrast enhancement techniques for this relatively small (357 aa) protein

• Nuclear Magnetic Resonance (NMR):

  • Uniform or selective isotopic labeling of recombinant sre-31

  • Solid-state NMR for structure determination in lipid environments

  • Solution NMR of solubilized domains (e.g., N-terminal or C-terminal segments)

• Molecular Dynamics Simulations:

  • Integration of experimental structural data with computational modeling

  • Simulation of protein dynamics in membrane environments

  • Prediction of conformational changes upon ligand binding

• Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS):

  • Mapping solvent-accessible regions

  • Identifying structural changes upon ligand binding

  • Detecting conformational flexibility

The His-tag present in commercially available recombinant sre-31 should be considered in structural studies, as it may influence protein behavior. Researchers may need to cleave the tag or demonstrate its lack of interference with native structure.

What specific challenges exist in identifying the physiological ligands for sre-31?

Identifying physiological ligands for orphan receptors like sre-31 presents unique challenges:

• Lack of Functional Information:

  • Limited knowledge about the natural signaling pathways of sre-31

  • Absence of known related receptors with characterized ligands

  • Uncertainty about the cellular/subcellular localization in C. elegans

• Technical Barriers:

  • Need for functional reconstitution systems mimicking native membrane environment

  • Requirement for sensitive detection methods for low-affinity interactions

  • Challenges in preparing diverse compound libraries relevant to C. elegans biology

• Candidate Ligand Selection Strategies:

  • Metabolomic profiling of C. elegans extracts

  • Bioinformatic prediction based on receptor structure

  • Screening chemically diverse natural product libraries

  • Testing compounds based on C. elegans habitat composition

• Validation Approach Complexity:

  • Need for multiple orthogonal binding assays

  • Challenges in designing relevant functional assays

  • Requirement for in vivo validation in C. elegans

• Methodological Solutions:

  • Unbiased screening approaches using label-free detection methods

  • Activity-guided fractionation of C. elegans extracts

  • Phenotypic screening of sre-31 knockout worms with candidate compounds

  • Heterologous expression systems coupled to reporter assays

The identification of related serpentine receptors in other organisms, such as those found in P. falciparum , may provide comparative insights to narrow down potential ligand classes.

How should researchers integrate recombinant sre-31 studies with in vivo C. elegans research?

Integrating recombinant protein studies with in vivo C. elegans research creates a comprehensive understanding of sre-31 biology:

• Complementary Experimental Design:

  • In vitro binding studies with recombinant sre-31 to identify candidate ligands

  • In vivo validation of binding partners in C. elegans

  • Structure-function studies combining mutagenesis of recombinant protein and transgenic worms

• Translational Research Workflow:

  • Initial high-throughput screening using recombinant protein

  • Secondary validation in cell-based assays

  • Tertiary confirmation in C. elegans models

  • Feedback loop to refine recombinant protein studies

• Genetic Approaches in C. elegans:

  • CRISPR/Cas9 editing to generate sre-31 mutations matching those studied in vitro

  • Tissue-specific expression of wild-type or mutant sre-31

  • Rescue experiments in knockout worms with variants characterized in vitro

• Physiological Relevance Assessment:

  • Behavioral assays in response to candidate ligands identified with recombinant protein

  • Calcium imaging in neurons expressing sre-31

  • Electrophysiological recordings from cells expressing native or recombinant sre-31

• Technological Bridges:

  • Development of antibodies against recombinant sre-31 for in vivo localization

  • Creation of fluorescently tagged versions for trafficking studies

  • Use of photoaffinity labels to identify interacting proteins in vivo

This integrated approach maximizes the research value of recombinant sre-31 preparations by connecting molecular-level findings to organismal biology.

How does sre-31 compare to other serpentine receptor classes in C. elegans?

C. elegans possesses an extraordinarily large number of serpentine receptors, which can be compared to sre-31:

• Receptor Family Diversity:

  • C. elegans genome encodes approximately 1,300 serpentine receptors

  • sre-31 belongs to the serpentine receptor class epsilon (sre) family

  • Other major families include str (seven transmembrane receptor), srd, srh, sri, etc.

• Comparative Structural Features:

• Functional Differentiation:

  • sre family receptors are hypothesized to function in chemosensation

  • Some serpentine receptor families have known roles in sensing specific chemicals or pheromones

  • Receptor families show differential expression patterns across tissues

• Evolutionary Relationships:

  • sre-31 likely arose through gene duplication events common in C. elegans receptor evolution

  • Different receptor families show varying degrees of conservation across nematode species

• Ligand Specificity:

  • Most C. elegans serpentine receptors remain orphan (without identified ligands)

  • Some families show specialization for specific chemical classes (e.g., ascarosides)

Understanding sre-31 in the context of this receptor superfamily can provide insights into its potential specialized functions and evolutionary significance.

What emerging technologies might advance the study of recombinant serpentine receptors?

Several emerging technologies show promise for advancing serpentine receptor research:

• Structural Biology Innovations:

  • Cryo-electron microscopy advances allowing structure determination of smaller membrane proteins

  • Microcrystal electron diffraction (MicroED) for crystallographic studies of membrane proteins

  • Serial femtosecond crystallography using X-ray free-electron lasers

• Membrane Mimetic Systems:

  • Polymer-based nanodiscs providing stable membrane environments

  • Cell-free expression systems coupled to immediate reconstitution

  • 3D-printed artificial cell membranes with controlled composition

• Functional Characterization Tools:

  • Label-free binding detection through interferometric scattering microscopy

  • Single-molecule FRET to detect conformational changes

  • Nanobody-based sensors for specific receptor conformations

  • Optogenetic control of receptor activity

• Computational Advances:

  • AI-driven structure prediction (AlphaFold2/RoseTTAFold)

  • Deep learning for binding site and ligand prediction

  • Molecular dynamics simulations with specialized membrane force fields

• High-Throughput Methodologies:

  • Microfluidic platforms for parallel receptor characterization

  • DNA-encoded library screening against membrane proteins

  • Massively parallel functional assays in droplet-based systems

These technologies could overcome current limitations in working with recombinant serpentine receptors like sre-31 and facilitate more comprehensive functional and structural studies.

What are the most significant open questions in sre-31 research?

Despite advances in recombinant protein technology, several critical questions remain unanswered in sre-31 research:

• Physiological Function:

  • What is the natural ligand or ligands for sre-31?

  • What signaling pathways does sre-31 activate in C. elegans?

  • Which physiological processes in C. elegans require sre-31 function?

• Structural Determinants:

  • What are the key residues involved in ligand binding?

  • How does the receptor transition between active and inactive conformations?

  • What is the three-dimensional structure of sre-31 in its native state?

• Evolutionary Significance:

  • Why has C. elegans maintained sre-31 throughout evolution?

  • How does sre-31 compare to homologs in other nematode species?

  • What selective pressures shaped sre-31's function?

• Therapeutic Potential:

  • Could sre-31 or its signaling pathway serve as targets for anthelmintic development?

  • Are there human disorders that could be modeled using sre-31 biology?

• Technical Developments:

  • How can we improve expression and purification of fully functional recombinant sre-31?

  • What are the optimal conditions for studying sre-31 outside its native membrane environment?

Addressing these questions will require integrated approaches combining recombinant protein biochemistry, structural biology, genetics, and in vivo studies in C. elegans. The availability of high-quality recombinant sre-31 preparations provides a foundation for these investigations.