Recombinant Human Olfactory receptor 8S1 (OR8S1)

What is Olfactory Receptor 8S1 (OR8S1)?

Olfactory Receptor 8S1 (OR8S1) is a member of the olfactory receptor family, which constitutes the largest mammalian protein superfamily . As an olfactory receptor, OR8S1 belongs to the G-protein coupled receptor 1 (GPCR) family , characterized by seven transmembrane domains. These receptors are primarily expressed in the olfactory epithelium and are responsible for the detection of odorant molecules, initiating a neuronal response that leads to the perception of smell. OR8S1, like other ORs, couples to the olfactory-specific G protein (Gαolf) to activate adenylyl cyclase, leading to increased intracellular cAMP levels when activated by its cognate ligands .

What is the structural classification of OR8S1?

OR8S1 is classified as a member of the G-protein coupled receptor 1 family , characterized by seven transmembrane domains connected by three extracellular and three intracellular loops. The N-terminus is located extracellularly while the C-terminus extends into the cytoplasm. Based on the naming convention for olfactory receptors, OR8S1 belongs to family 8, subfamily S, and is the first member of this subfamily. The structural features of OR8S1 include conserved domains common to many olfactory receptors, which are critical for proper folding, trafficking to the cell surface, and interaction with both odorant molecules and downstream signaling components.

How does OR8S1 compare to other human olfactory receptors?

The human olfactory receptor repertoire contains approximately 400 functional genes and a similar number of pseudogenes . OR8S1 is one of these functional ORs. Like other ORs, it is subject to copy-number variation (CNV) which can affect the number of functional copies present in an individual's genome . Research has shown that different ORs vary significantly in their cell surface expression levels when heterologously expressed, with some requiring accessory proteins such as RTP1S (Receptor Transporting Protein 1, Short) for efficient trafficking . Comparative analysis of OR sequences reveals that certain structural features correlate with their ability to reach the cell surface independent of chaperone proteins . The availability of antibodies for OR8S1 suggests it is among the more studied ORs.

What are the common methods for detecting OR8S1 expression?

Several methods are commonly employed to detect OR8S1 expression:

• Western Blot analysis: Using specific antibodies such as rabbit polyclonal antibodies against OR8S1 (e.g., A100833), which has been validated for use with human samples . Western blots can detect OR8S1 protein in cell lysates, as demonstrated with HT-29 cells and various other cell lines .

• ELISA (Enzyme-Linked Immunosorbent Assay): Another validated method using anti-OR8S1 antibodies to quantify OR8S1 protein levels .

• RT-PCR and qPCR: For detecting OR8S1 mRNA expression levels in tissues or cell lines.

• Immunohistochemistry/Immunofluorescence: Using labeled antibodies to visualize the spatial distribution of OR8S1 in tissue sections or cells.

• Epitope tagging: Adding tags such as FLAG, Rho-tag, or Lucy-tag to the N-terminus of recombinant OR8S1 for detection using tag-specific antibodies, which is particularly useful when studying heterologously expressed receptors .

What are the optimal experimental conditions for studying OR8S1 function?

Optimizing experimental conditions for studying OR8S1 function requires careful consideration of several factors:

Expression System:

• HEK293 cells are commonly used for heterologous expression of ORs

• Co-expression with RTP1S significantly improves cell surface expression of many ORs

• Addition of Gαolf and Ric-8B enhances the coupling of ORs to the cAMP signaling pathway

Tagging Strategies:

• N-terminal tags are preferred, with options including:

  • Rho-tag (rhodopsin-derived signal peptide)

  • Lucy-tag

  • IL-6-Halo-tag

  • These tags have shown varying efficiency in promoting cell surface expression

Functional Assay Systems:

• cAMP-dependent luciferase reporters (e.g., CRE/luc2PpGL4.29) allow for sensitive detection of OR activation

• GloSensor™ system provides high sensitivity for cAMP detection

• Calcium imaging can be used if the OR is coupled to appropriate G proteins

• Microwell array systems permit high-throughput screening of odorant responses

Transfection Protocol:

• For 384-well plate assays: ~0.029 μg OR vector, 0.022 μg CRE/luc2PpGL4.29, 0.0011 μg pRL-CMV, and 0.012 μg RTP1S vectors per well

• When including Gαolf: 0.029 μg OR vector, 0.011 μg CRE/luc2PpGL4.29, 0.0011 μg pRL-CMV, 0.012 μg RTP1S, and 0.010 μg Gαolf vectors per well

Odorant Application:

• Odorant solutions are typically diluted in growth medium without FBS or in Ringer's solution (140 mM NaCl, 5 mM KCl, 1 mM MgCl₂)

• Concentrations generally range from 0.01–0.1 mM for simple odorants and 0.05–5.0 mM for complex odorants

How can copy-number variations in OR8S1 affect experimental outcomes?

Copy-number variations (CNVs) in OR8S1 can significantly impact experimental outcomes in several ways:

Variable Expression Levels:

• Individuals with different copy numbers of OR8S1 may show different expression levels in native tissues, complicating the interpretation of clinical samples

• When cloning from genomic DNA, researchers may inadvertently select variants with altered function

Genetic Background Effects:

• CNVs have created a "mosaic of OR dosages across persons" , meaning that the genetic background used for experiments may not be representative of the general population

• Approximately 50% of OR CNVs involve multiple OR genes, potentially affecting regulatory elements or creating fusion genes

Evolutionary Considerations:

• Human-specific deletion alleles have profoundly affected individual OR gene content , suggesting that some variants may have altered function or regulatory patterns

• CNVs are more frequent among OR pseudogenes than intact genes, indicating selective constraints on functional ORs

Experimental Design Implications:

• Researchers should sequence their cloned OR8S1 constructs to identify any variants

• Comparisons between studies may be complicated by the use of different OR8S1 variants

• Population studies should account for CNV frequency, which may differ between populations

What are the validated cellular models for studying OR8S1?

Several cellular models have been validated for studying olfactory receptors, including OR8S1:

HEK293 Cells:

• The most commonly used heterologous expression system for ORs

• Advantages include easy transfection, rapid growth, and minimal endogenous GPCR expression

• Require co-expression of accessory proteins for optimal OR expression

HT-29 Cells:

• Western blot analysis has confirmed endogenous expression of OR8S1 in these human colorectal adenocarcinoma cells

• Useful for studying native OR8S1 expression and function without the need for transfection

Other Cell Lines:

• Western blot validation has shown OR8S1 expression in multiple cell lines

• These could serve as alternative models for studying endogenous OR8S1 function

Cell Array Systems:

• Advanced microwell array systems with ~400-500 OR-expressing cells per well allow for high-throughput screening

• These systems enable simultaneous and real-time measurement of responses from multiple ORs to specific odorants

How does OR8S1 trafficking to the cell surface differ from other ORs?

The efficient trafficking of ORs to the cell surface is a critical challenge in studying these receptors, as many are retained in the endoplasmic reticulum when heterologously expressed. While specific information about OR8S1 trafficking is not explicitly provided in the search results, general principles and comparative aspects can be outlined:

General OR Trafficking Challenges:

• Many ORs are retained in the endoplasmic reticulum due to misfolding or recognition by quality control mechanisms

• This retention has necessitated the development of specialized expression systems with chaperone proteins

Role of Accessory Proteins:

• RTP1S (a C-terminal shortened version of RTP1) significantly improves cell surface expression of many ORs

• The exact dependency of OR8S1 on RTP1S would need to be experimentally determined

Structural Determinants:

• Recent research has identified common structural features of ORs that can reach the cell surface independent of RTPs

• These features include specific amino acid compositions and motifs in the transmembrane domains and loops

Alternative Strategies for Improving Trafficking:

• Co-expression with non-OR GPCRs (such as β2-adrenergic receptor or M3 muscarinic acetylcholine receptor) can improve OR trafficking through heterodimer formation

• The M3 muscarinic receptor has been found to suppress β-arrestin 2-mediated OR internalization

What are the best practices for validating anti-OR8S1 antibodies?

Validating antibodies is crucial for ensuring reliable results in OR8S1 research. Based on the search results and standard practices in antibody validation, the following approaches are recommended:

Western Blot Validation:

• Test the antibody against lysates from cells known to express OR8S1 (e.g., HT-29 cells)

• Include negative control cell lines that do not express OR8S1

• Perform peptide competition assays where the antibody is pre-incubated with the immunizing peptide before Western blot analysis

• Verify that the observed band is at the expected molecular weight for OR8S1

Specificity Testing:

• Test against heterologously expressed OR8S1 with epitope tags for confirmation

• Test against closely related ORs to ensure the antibody doesn't cross-react

• Consider knockout/knockdown controls where OR8S1 expression is eliminated or reduced

Multiple Detection Methods:

• Validate the antibody using both Western blot and ELISA techniques

• Consider additional methods such as immunohistochemistry or immunofluorescence

• Flow cytometry can be used to assess cell surface expression in non-permeabilized cells

Application-Specific Validation:

• Optimize antibody concentration for each application (Western blot, ELISA, immunofluorescence)

• Determine appropriate blocking conditions to minimize background

• Establish optimal incubation times and temperatures

How can one troubleshoot low expression levels of recombinant OR8S1?

Troubleshooting low expression levels of recombinant OR8S1 requires a systematic approach to identify and address potential issues:

Vector and Construct Design:

• Verify the sequence integrity of the OR8S1 construct

• Ensure the presence of strong promoters (e.g., CMV) and proper Kozak sequence

• Consider codon optimization for the host cell line

• Add trafficking-enhancing tags such as Rho-tag, Lucy-tag, or IL-6-Halo-tag

Accessory Protein Co-expression:

• Ensure co-transfection with RTP1S, which significantly improves surface expression of many ORs

• Consider co-expression with non-OR GPCRs (β2-adrenergic receptor, M3 muscarinic acetylcholine receptor) which can form heterodimers with ORs and enhance trafficking

• Add Gαolf and Ric-8B to improve signaling capabilities

Transfection Optimization:

• Optimize the ratio of OR8S1 plasmid to accessory protein plasmids

  • For 96-well plate assays: 0.075 μg OR vector, 0.03 μg CRE/luc2PpGL4.29, 0.03 μg pRL-CMV, and 0.03 μg RTP1S vector per well

  • For 384-well plate assays: approximately 0.029 μg OR vector, 0.022 μg CRE/luc2PpGL4.29, 0.0011 μg pRL-CMV, and 0.012 μg RTP1S vector per well

• Test different transfection reagents and protocols

• Consider stable integration rather than transient transfection

Cell Culture Conditions:

• Use poly-D-lysine coated plates to improve cell adherence

• Optimize cell density at transfection

• Ensure consistent culture conditions (37°C, 5% CO₂)

Detection Methods:

• Use high-sensitivity detection methods

• For functional assays, consider GloSensor™ technology for improved cAMP detection

• For protein detection, use validated antibodies against OR8S1 or epitope tags

What are the optimal transfection conditions for OR8S1 expression?

Optimal transfection conditions for OR8S1 expression can be derived from the protocols described in the search results for olfactory receptors in general:

Plasmid Combinations and Ratios:

• For 96-well plate assays in HEK293 cells :

  • 0.075 μg FLAG-Rho-tagged OR8S1 pME18S vector

  • 0.03 μg CRE/luc2PpGL4.29 (CRE-dependent firefly luciferase)

  • 0.03 μg pRL-CMV (constitutively expressed Renilla luciferase)

  • 0.03 μg RTP1S pME18S vector

• For 384-well plate assays in HEK293 cells :

  • 0.029 μg FLAG-Rho-tagged OR8S1 pME18S vector

  • 0.022 μg CRE/luc2PpGL4.29

  • 0.0011 μg pRL-CMV

  • 0.012 μg RTP1S pME18S vector

• When including Gαolf for enhanced signaling :

  • 0.029 μg FLAG-Rho-tagged OR8S1 pME18S

  • 0.011 μg CRE/luc2PpGL4.29

  • 0.0011 μg pRL-CMV

  • 0.012 μg RTP1S pME18S

  • 0.010 μg Gαolf pME18S

Cell Preparation:

• Use poly-D-lysine coated plates to improve cell adherence

• Optimal cell density: approximately 4 × 10^5 cells/cm² in the transfection mixture

Transfection Protocol:

• Prepare transfection complexes according to the manufacturer's protocol

• Add cell suspension to the transfection solution

• Incubate at 37°C in 5% CO₂ for 24 hours before assaying

Vector Selection:

• pME18S vector has been successfully used for OR expression

• The vector should contain a strong promoter (e.g., CMV)

N-Terminal Modifications:

• Add FLAG tag for detection

• Include Rho-tag (20 N-terminal amino acids of bovine rhodopsin) to enhance trafficking

• Consider alternative tags such as Lucy-tag or IL-6-Halo-tag

How can the OR8S1 receptor be properly tagged without disrupting function?

Proper tagging of the OR8S1 receptor requires careful consideration to enhance expression while preserving function:

N-Terminal Tags for Enhanced Trafficking:

• Rho-tag: The first 20 amino acids of bovine rhodopsin can be added to the N-terminus to enhance trafficking

• Lucy-tag: An alternative tag that has shown improved surface expression for some ORs compared to the Rho-tag

• IL-6-Halo-tag: Another option that may provide better surface expression for certain ORs

Epitope Tags for Detection:

• FLAG tag: Commonly used and can be added to the N-terminus along with trafficking tags

• Examples from the literature include FLAG-Rho-tagged OR constructs

Tag Positioning Considerations:

• N-terminal tagging is preferred for ORs as it generally interferes less with function

• The tag should be positioned after the initiator methionine

• When using multiple tags, the ordering typically follows: initiator methionine > epitope tag (e.g., FLAG) > trafficking tag (e.g., Rho) > OR sequence

Linker Sequences:

• Consider adding short flexible linkers (e.g., Gly-Ser repeats) between tags and the OR to reduce steric hindrance

• The linker should be designed to minimize disruption of the first transmembrane domain

Functional Validation:

• Always verify that the tagged receptor retains functionality using appropriate assays

• Compare responses of tagged and untagged versions when possible

• Dose-response curves can reveal subtle effects of tagging on receptor pharmacology

What are the recommended protocols for measuring OR8S1 activation?

Several protocols can be used to measure OR8S1 activation, based on the general methods described for olfactory receptors:

Luciferase Reporter Assays:

• cAMP-dependent luciferase reporters (e.g., CRE/luc2PpGL4.29) provide a sensitive readout of OR activation

• Protocol overview:

  • Transfect cells with OR8S1, accessory proteins, and reporter constructs

  • After 24 hours, treat with test compounds

  • Measure firefly luciferase activity (stimulation-dependent)

  • Normalize to Renilla luciferase activity (constitutive expression)

• Specific transfection ratios for 96-well format :

  • 0.075 μg OR vector

  • 0.03 μg CRE/luc2PpGL4.29

  • 0.03 μg pRL-CMV

  • 0.03 μg RTP1S vector

GloSensor™ cAMP Assay:

• Provides high sensitivity for real-time cAMP detection

• Allows kinetic measurements of OR responses

• Particularly useful for ORs with transient or low-magnitude responses

Microwell Array Systems:

• Human olfactory receptor-expressing cell array sensors allow simultaneous measurement of multiple ORs

• Uses approximately 400-500 OR-expressing cells per 0.5 mm square microwell

• Real-time monitoring under a fluorescence microscope equipped with a video camera

• Odorants are typically dissolved in Ringer's solution at concentrations of 0.01–0.1 mM for simple molecules or 0.05–5.0 mM for complex molecules

Odorant Application:

• Prepare odorants in growth medium without FBS or in Ringer's solution (140 mM NaCl, 5 mM KCl, 1 mM MgCl₂)

• For dose-response relationships, test multiple concentrations (typically 0.01–0.1 mM for simple odorants, 0.05–5.0 mM for complex odorants)

• Include vehicle controls and positive controls

How can one distinguish between specific and non-specific binding in OR8S1 studies?

Distinguishing between specific and non-specific binding is critical for accurately characterizing OR8S1-ligand interactions:

Experimental Approaches:

Dose-Response Relationships:

• Specific binding typically shows saturable dose-response curves

• Plot responses across a wide concentration range (e.g., 0.01–0.1 mM for simple odorants to 0.05–5.0 mM for complex molecules)

• Calculate EC50 values as measures of potency

Competitive Binding Assays:

• If a known ligand exists, competitive displacement can demonstrate binding site specificity

• Increasing concentrations of an unlabeled competitor should progressively reduce the response to a fixed concentration of the known ligand

Structure-Activity Relationships:

• Test structurally related compounds to map binding determinants

• Specific binding typically shows clear structure-activity relationships

• Minor structural changes in the ligand should have predictable effects on binding affinity

Controls and Validation:

Negative Controls:

• Empty vector-transfected cells to control for endogenous responses

• Cells expressing an unrelated OR to control for non-specific activation

• Vehicle controls to account for solvent effects

Positive Controls:

• Well-characterized OR-ligand pairs as system validation

• Direct activators of the signaling pathway (e.g., forskolin) as pathway controls

Receptor Expression Verification:

• Confirm OR8S1 expression using Western blot with anti-OR8S1 antibodies

• Verify cell surface expression using surface biotinylation or immunofluorescence with epitope tags

What are the recommended controls when studying OR8S1 in functional assays?

When conducting functional assays with OR8S1, several controls are essential to ensure reliable and interpretable results:

Negative Controls:

• Mock-transfected cells (transfection reagent only)

• Empty vector-transfected cells

• Cells expressing an unrelated OR that is not expected to respond to the test compounds

• Vehicle controls (solvent used to dissolve odorants) to account for potential solvent effects

Positive Controls:

• Cells expressing a well-characterized OR with known ligands

• Forskolin treatment to directly activate adenylyl cyclase, bypassing receptor activation

• If available, cells expressing OR8S1 with a known agonist

Specificity Controls:

• Dose-response relationships to demonstrate concentration-dependent effects

• Structurally related compounds to establish structure-activity relationships

• Mutant OR8S1 with alterations in predicted binding residues

Transfection Efficiency Controls:

• Co-transfection with a constitutively expressed reporter gene (e.g., pRL-CMV for Renilla luciferase)

• This allows normalization of the signal to account for variations in transfection efficiency

Signal Pathway Controls:

• Inhibitors of the cAMP pathway to confirm the specificity of the observed signal

• Positive controls for the cAMP pathway (e.g., β-adrenergic agonists)

Expression Controls:

• Western blot or immunofluorescence with anti-OR8S1 antibodies to confirm expression

• Surface expression verification using non-permeabilized cells with antibodies against N-terminal tags

How does genetic variation in OR8S1 impact its function?

Genetic variation in OR8S1, like other olfactory receptors, can significantly impact its function:

Single Nucleotide Polymorphisms (SNPs):

• SNPs in the coding region can alter amino acid sequence, potentially affecting:

  • Protein folding and stability

  • Trafficking to the cell surface

  • Ligand binding specificity or affinity

  • G protein coupling efficiency

• When amplifying OR genes from human genomic DNA, researchers have identified SNPs that differ from reference sequences but are found in the NCBI dbSNP database

Copy Number Variations (CNVs):

• ORs frequently occur in genomic regions affected by CNVs

• These variations can affect gene dosage and potentially expression levels

• CNVs may involve multiple OR genes, with some spanning up to 11 loci

• Deletion alleles specific to humans have had a "profound effect" on individual OR gene content

Evolutionary Implications:

• ORs with a close human paralog or lacking a one-to-one ortholog in chimpanzee are enriched for CNVs

• There is an enrichment of CNV losses over gains in ORs lacking a chimpanzee ortholog, potentially related to the known diminution of the human OR repertoire

Functional Consequences:

• Genetic variation may contribute to individual differences in odor perception

• Some variants may result in non-functional receptors or altered response profiles

• When using heterologous expression systems, it's important to consider which variant of OR8S1 is being used

What is known about the evolution of OR8S1 compared to other olfactory receptors?

While the search results don't provide specific information about OR8S1 evolution, general principles regarding olfactory receptor evolution can be applied:

Evolutionary Pressure on Olfactory Receptors:

• The human OR gene repertoire has experienced considerable reduction compared to other mammals

• Approximately 55% of human OR genes are pseudogenes

• CNVs have played an important role in the evolution of the human olfactory repertoire

Copy Number Variations:

• ORs with a close human paralog or lacking a one-to-one ortholog in chimpanzee show enrichment for CNVs

• Among ORs lacking a chimpanzee ortholog, there is an enrichment in CNV losses over gains, potentially related to the diminution of the human OR repertoire

• These patterns suggest ongoing evolutionary processes affecting the human OR repertoire

Human-Specific Changes:

• Comparison to the chimpanzee reference genome has revealed human-derived deletion alleles affecting OR genes

• These deletions have had a profound effect on individual OR gene content

• Such changes reflect the reduced reliance on olfaction in human evolution compared to other primates

Selective Constraints:

How can OR8S1 research contribute to understanding olfactory perception?

OR8S1 research can contribute to understanding olfactory perception in several important ways:

Receptor-Ligand Relationships:

• Identifying the specific odorants that activate OR8S1 adds to our understanding of the combinatorial code of olfaction

• Structure-activity relationships of OR8S1 ligands can reveal the molecular features important for receptor activation

Individual Variation:

• Studies of OR8S1 genetic variants can help explain individual differences in odor perception

• Copy number variations affecting OR8S1 may correlate with specific olfactory phenotypes

Signaling Mechanisms:

• Understanding OR8S1 signaling pathways contributes to knowledge of how olfactory information is processed

• Differences in signaling efficiency or dynamics between OR8S1 and other ORs may explain unique aspects of the perception of its ligands

Evolutionary Perspective:

• Comparing OR8S1 sequence and function across species can reveal evolutionary adaptations in olfactory perception

• Human-specific changes in OR8S1 may reflect environmental or dietary adaptations in human evolution

Clinical Applications:

• OR8S1 research may help understand olfactory dysfunction in various clinical conditions

• Variations in OR8S1 could potentially serve as genetic markers for specific anosmias or hyposmias

What new methodologies are being developed for OR8S1 and other olfactory receptor research?

Several innovative methodologies are being developed for olfactory receptor research:

High-Throughput Screening Systems:

• Human olfactory receptor-expressing cell array sensors with approximately 400-500 OR-expressing cells per microwell

• These systems enable simultaneous and real-time measurement of responses from multiple ORs to specific odorants

• Automated laboratory systems (e.g., BiomekFX) for handling 384-well plate assays

Improved Expression Systems:

• Enhanced trafficking tags such as Lucy-tag and IL-6-Halo-tag that may provide better surface expression than traditional Rho-tag for some ORs

• Co-expression of non-OR GPCRs (e.g., β2-adrenergic receptor, M3 muscarinic acetylcholine receptor) to form heterodimers with ORs and improve their sorting to the cell surface

• Systems to suppress β-arrestin 2-mediated OR internalization

Enhanced Signal Detection:

• GloSensor™ technology providing highly sensitive detection of cAMP

• Improved second messenger generation and detection systems through co-expression of olfactory-specific G protein α (GNAL/Gαolf) and Ric-8B (a chaperone of Gα protein)

Structural Biology Approaches:

• Computational modeling based on structural features of ORs that correlate with their ability to reach the cell surface independent of chaperone proteins

• Advanced imaging techniques to visualize OR-ligand interactions

Genomic Analysis:

• High-resolution copy-number variation mapping of OR genes

• Integration of genomic data with functional assays to understand the impact of genetic variation