Recombinant Saccharomyces cerevisiae UPF0674 endoplasmic reticulum membrane protein YNR021W (YNR021W)

What is YNR021W and where is it localized in Saccharomyces cerevisiae?

YNR021W is a putative protein classified as an endoplasmic reticulum membrane protein in Saccharomyces cerevisiae (strain ATCC 204508/S288c). Green fluorescent protein (GFP) fusion studies have confirmed its localization to the endoplasmic reticulum . The protein is encoded by the YNR021W gene (also known by ORF name N3216) and is not essential for yeast viability. The complete mature protein spans residues 2-404 and contains multiple transmembrane domains that anchor it within the ER membrane .

What are the known protein interactions of YNR021W?

According to BioGRID database information, YNR021W is involved in a substantial interaction network comprising 137 interactions with 109 other proteins . Many of these interactions involve components of the endoplasmic reticulum stress response machinery, suggesting a potential role in cellular stress adaptation. Additionally, the protein has 8 documented post-translational modification (PTM) sites that may regulate its function or interactions . Researchers investigating YNR021W should consider these interaction partners when designing experiments to elucidate its functional role.

How can recombinant YNR021W protein be efficiently expressed and purified?

To express and purify recombinant YNR021W protein, researchers have successfully employed E. coli expression systems with N-terminal His-tagging. The procedure involves:

• Construct preparation: Clone the YNR021W gene (coding for residues 2-404) into an expression vector with an N-terminal His-tag.

• Expression in E. coli: Transform the construct into an appropriate E. coli strain and induce protein expression.

• Purification: Perform affinity chromatography using nickel columns to capture the His-tagged protein.

• Final preparation: Lyophilize the purified protein in Tris/PBS-based buffer containing 6% Trehalose at pH 8.0 .

For optimal stability and activity, the recombinant protein should be reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL, with 5-50% glycerol added as a cryoprotectant for long-term storage at -20°C/-80°C. Working aliquots can be maintained at 4°C for up to one week, but repeated freeze-thaw cycles should be avoided as they may compromise protein integrity .

What are the recommended storage conditions for maintaining YNR021W protein stability?

Optimal storage conditions for YNR021W protein are critical for maintaining its structural integrity and activity. Based on experimental protocols:

• Long-term storage: Store lyophilized powder or aliquoted solutions at -20°C/-80°C.

• Buffer composition: Use Tris/PBS-based buffer containing 6% Trehalose at pH 8.0.

• Cryoprotection: Add glycerol to a final concentration of 50% for freezer storage.

• Working conditions: Keep working aliquots at 4°C for no more than one week.

• Freeze-thaw management: Minimize freeze-thaw cycles as they significantly reduce protein stability .

For researchers conducting extended experiments, it is recommended to prepare multiple small-volume aliquots rather than repeatedly accessing a single stock solution.

What is the relationship between YNR021W and the unfolded protein response (UPR) in yeast?

While YNR021W's specific function remains to be fully characterized, several lines of evidence suggest its involvement in the unfolded protein response (UPR) pathway:

• Its localization to the endoplasmic reticulum, the primary site of UPR activation.

• Its classification as an ER membrane protein potentially involved in ER stress sensing or signaling.

• Expression pattern changes observed during UPR activation experiments .

The UPR in Saccharomyces cerevisiae is primarily mediated through the Ire1-Hac1 pathway. Under ER stress conditions, Ire1 promotes splicing of HAC1u mRNA to yield HAC1i mRNA, which is translated into the Hac1 transcription factor. This factor then induces numerous UPR target genes, including those encoding ER chaperones like BiP (Kar2), protein-folding enzymes, and enzymes for membrane lipid biogenesis .

Research indicates that constitutive activation of UPR through HAC1i expression leads to significant ER expansion, which can be exploited for metabolic engineering purposes. The relationship between YNR021W and this process represents an important area for further investigation .

How can YNR021W be used in visualizing organelle contact sites?

YNR021W has been successfully employed in split-GFP systems for visualizing organelle contact sites in Saccharomyces cerevisiae, particularly at the endoplasmic reticulum interface. The methodology involves:

• Construct preparation: Generate a plasmid expressing YNR021W fused with GFP11 at its C-terminus (e.g., pRS314-GPDp-YNR021W-GFP11).

• Expression system: Use a strong promoter like GPD and appropriate terminator (CYC1).

• Complementary constructs: Express complementary GFP1-10 fragments fused to proteins localizing to other organelles of interest.

• Visualization: When the organelles come into proximity, the split GFP fragments complement each other, resulting in fluorescence that can be detected by microscopy .

This system allows researchers to dynamically monitor inter-organelle contacts involving the ER. The split-GFP approach offers advantages over conventional methods by providing real-time visualization of transient interactions between organelles, which is critical for understanding dynamic cellular processes .

How can YNR021W and ER membrane proteins be utilized for metabolic engineering in Saccharomyces cerevisiae?

ER membrane proteins, including YNR021W, can be leveraged for metabolic engineering applications through several strategies:

• ER expansion approaches: Overexpression of key ER regulatory factors like INO2 expands the ER membrane system, which can enhance ER protein synthesis and folding capacity, relieving metabolic constraints imposed by limited enzyme abundance .

• UPR modulation: Controlled activation of the UPR pathway through genetic modifications can increase production of valuable lipidic molecules. For instance, constitutive expression of HAC1i mRNA in combination with mild ER stress stimuli has been shown to significantly increase production of triglycerides and heterologous carotenoids .

• Membrane protein overexpression: Strategic overexpression of specific ER membrane proteins can alter cellular metabolism to favor desired pathways. For example, targeting terpene biosynthesis has yielded remarkable improvements:

These approaches demonstrate how manipulation of ER membrane composition and function can drastically rewire metabolic networks to enhance production of valuable compounds .

What role might YNR021W play in ER stress adaptation during metabolic engineering?

Although YNR021W's precise function remains uncharacterized, insights from related ER membrane protein studies suggest potential roles in stress adaptation during metabolic engineering:

• ER membrane expansion: YNR021W may contribute to the physical expansion of the ER during stress, which has been observed to significantly increase in cells with constitutively active UPR .

• Membrane homeostasis: As an ER membrane protein, YNR021W might participate in maintaining membrane integrity during ER stress conditions, which is essential for cell survival during metabolic engineering procedures that often impose significant stress.

• Protein quality control: It may interact with components of the ER-associated degradation (ERAD) machinery, which becomes critical when heterologous proteins are overexpressed.

Research has shown that cells constitutively expressing HAC1i mRNA, which activates the UPR pathway, exhibit an expanded ER with complicated morphologies. This expansion correlates with enhanced production of triglycerides and heterogenous carotenoids, suggesting that ER membrane proteins like YNR021W may play supporting roles in facilitating this metabolic shift .

What controls should be included when investigating YNR021W function through gene deletion or overexpression?

When designing experiments to investigate YNR021W function through genetic manipulation, the following controls should be included:

• Wild-type strain: The parent strain without any modifications (e.g., BY4742 for S288C-based experiments) serves as the primary control for all comparisons .

• Empty vector control: For overexpression studies, include cells transformed with the same expression vector lacking the YNR021W insert.

• Non-related gene controls: Include strains with deletion or overexpression of non-related genes to control for general effects of genetic manipulation.

• Complementation control: For deletion studies, include a strain where YNR021W has been reintroduced to verify that observed phenotypes are specifically due to the absence of YNR021W.

• UPR pathway controls: Include strains with known UPR pathway modifications (e.g., HAC1i expression, IRE1 deletion) to contextualize YNR021W results within the broader stress response network .

Furthermore, researchers should monitor growth rates, ER morphology, and UPR activation (e.g., by measuring KAR2 mRNA levels using RT-qPCR) to comprehensively assess the impact of YNR021W manipulation .

How can researchers effectively use fluorescent protein tagging to study YNR021W localization and dynamics?

Effective fluorescent protein tagging of YNR021W requires careful consideration of several factors:

• Tag position: Both C-terminal and N-terminal tagging approaches should be tested, as the optimal position depends on the protein's topology. For YNR021W, C-terminal tagging has been successfully employed in split-GFP systems .

• Linker design: Include a flexible linker (e.g., GSGSGS) between YNR021W and the fluorescent tag to minimize interference with protein folding and function.

• Expression control: Use an appropriate promoter—native promoter for physiological expression levels or an inducible promoter (e.g., GAL1) for controlled expression studies.

• Verification methods: Confirm proper localization and function through:

  • Western blotting to verify fusion protein expression at the expected size

  • Complementation assays if studying a deletion strain

  • Co-localization with known ER markers

• Live-cell imaging considerations: For dynamic studies, minimize phototoxicity by using lower light intensity and appropriate exposure times. Consider techniques like FRAP (Fluorescence Recovery After Photobleaching) to study protein mobility within the ER membrane.

The split-GFP system has been particularly useful for studying YNR021W at organelle contact sites, where GFP11 is fused to YNR021W and expressed under the GPD promoter with a CYC1 terminator .

How might gene amplification methods be applied to enhance YNR021W studies in S. cerevisiae?

Advanced gene amplification strategies can significantly enhance YNR021W research through several approaches:

• Extrachromosomal circular DNA (eccDNA) formation: Studies have demonstrated that genes placed near Autonomously Replicating Sequences (ARS) can spontaneously form eccDNA elements in S. cerevisiae during adaptive evolution. This approach could be utilized to amplify YNR021W copy number by:

  • Integrating YNR021W near an ARS sequence (e.g., ARS1529)

  • Applying selective pressure that favors YNR021W amplification

  • Monitoring for eccDNA formation using outward-facing PCR primers

• Tandem amplification integration: Following eccDNA formation, these circular elements can reintegrate into the genome as tandem arrays. This has been observed with other genes, where copy numbers increased approximately 9-fold, significantly enhancing protein expression levels .

• Copy number verification: Researchers should verify amplification through:

  • Southern blot analysis using probes that hybridize to YNR021W

  • qPCR assays to quantify copy number

  • Whole genome sequencing to identify precise integration sites

This approach could be particularly valuable for studying YNR021W function by creating a gradient of expression levels correlating with different copy numbers, potentially revealing phenotypes not observable at normal expression levels.

How can YNR021W be leveraged in immunological studies and vaccine development?

YNR021W can be employed in immunological applications through recombinant S. cerevisiae platforms, building on established techniques for yeast-based vaccine development:

• Antigen delivery system: YNR021W can be used as a fusion partner for antigenic proteins or peptides, potentially enhancing their presentation on the ER membrane or cell surface. Recombinant S. cerevisiae expressing such fusion constructs can be utilized as whole-cell vaccines.

• Adjuvant properties: Recombinant yeast cells have demonstrated natural adjuvant properties through their interaction with dendritic cells (DCs). S. cerevisiae treatment of immature DCs results in:

  • Rapid elevation of MHC class I and class II molecules

  • Upregulation of costimulatory molecules and DC maturation markers

  • Secretion of Type I inflammatory cytokines

  • Enhanced allospecific reactivity

• Immune response optimization: Vaccine formulations utilizing YNR021W fusions should be evaluated for their ability to elicit both CD4+ and CD8+ immune responses, as has been demonstrated with other yeast-expressed antigens .

• Safety profile: S. cerevisiae-based vaccines have demonstrated excellent safety profiles, allowing for multiple administrations in vaccination protocols, which is particularly advantageous for therapeutic cancer vaccines or vaccines targeting chronic infectious diseases .

This approach leverages the natural immunostimulatory properties of yeast while potentially utilizing YNR021W's ER localization to influence antigen processing and presentation pathways.

What are the most promising approaches for elucidating the precise function of YNR021W?

Given the current limited understanding of YNR021W's specific function, several promising research approaches could advance our knowledge:

• Comprehensive phenotypic analysis: Conduct detailed phenotypic characterization of YNR021W deletion and overexpression strains under various stress conditions, particularly focusing on ER stress, lipid metabolism perturbations, and growth in different carbon sources.

• High-resolution interactome mapping: Employ techniques like BioID or proximity labeling to identify proteins that interact with YNR021W under different cellular conditions, potentially revealing functional associations.

• Structural biology approaches: Determine the 3D structure of YNR021W through X-ray crystallography or cryo-EM to gain insights into potential functional domains and interaction surfaces.

• Evolutionary analysis: Compare YNR021W with homologs in other yeast species to identify conserved regions that might indicate functional importance.

• Integration with systems biology: Incorporate YNR021W into existing models of the UPR and ER stress response networks, using computational approaches to predict its role and design targeted experiments to test these predictions.

• CRISPR-based screens: Conduct synthetic genetic array analysis or CRISPR screens to identify genetic interactions that might reveal functional relationships.

These approaches, particularly when combined, offer promising avenues for uncovering the biological role of this currently enigmatic membrane protein.

How might YNR021W contribute to the expanding toolkit for metabolic engineering of yeast?

YNR021W and related ER membrane proteins represent valuable additions to the metabolic engineering toolkit through several potential applications:

• ER expansion strategies: Building on research showing that ER expansion enhances metabolic output, YNR021W could be incorporated into expression cassettes designed to modify ER architecture and function .

• Stress resistance engineering: If YNR021W proves to have stress-protective functions, its controlled expression could enhance yeast robustness during industrial fermentation processes that involve high osmotic pressure, ethanol stress, or other challenging conditions.

• Protein production platforms: For heterologous protein expression, particularly secreted or membrane proteins, YNR021W could be co-expressed to potentially enhance ER capacity and quality control.

• Lipid production optimization: Given the connection between ER membrane proteins, UPR activation, and enhanced lipid production, YNR021W manipulation could be integrated into strategies for producing high-value lipids and lipid-derived compounds .

• Synergistic gene combinations: Combining YNR021W expression with other modifications like HAC1i expression or INO2 overexpression might yield synergistic improvements in metabolic output beyond what individual modifications achieve .

As our understanding of YNR021W function improves, its strategic deployment in metabolic engineering applications will likely expand, potentially contributing to next-generation production platforms for biofuels, pharmaceuticals, and other valuable compounds.

What are common issues when working with recombinant YNR021W protein and how can they be addressed?

Researchers working with recombinant YNR021W often encounter several challenges that can be addressed through specific methodological approaches:

• Low expression yields:

  • Optimize codon usage for E. coli expression

  • Test different E. coli strains (BL21(DE3), Rosetta, etc.)

  • Reduce expression temperature (16-20°C)

  • Use stronger lysis buffers containing appropriate detergents for membrane protein extraction

• Protein aggregation:

  • Include stabilizing agents (glycerol, trehalose) in all buffers

  • Maintain protein solutions at concentrations below 1.0 mg/mL

  • Perform purification at 4°C throughout the entire process

  • Consider adding mild detergents (0.01-0.05% DDM or LDAO)

• Loss of activity after freeze-thaw:

  • Prepare single-use aliquots

  • Include 50% glycerol in storage buffer

  • Use flash-freezing in liquid nitrogen rather than slow freezing

  • Store at -80°C rather than -20°C for long-term storage

• Poor solubility:

  • Engineer truncated versions lacking transmembrane domains

  • Use fusion tags that enhance solubility (MBP, SUMO) in addition to His-tag

  • Test different buffer conditions (pH range 6.0-8.5)

  • Consider refolding protocols if necessary

Following these empirically validated approaches can significantly improve the yield and quality of recombinant YNR021W protein preparations for downstream applications.

How can researchers address data inconsistencies when studying YNR021W in different strain backgrounds?

When inconsistencies arise in YNR021W studies across different strain backgrounds, researchers should implement a systematic approach to identify and address potential sources of variation:

• Strain background documentation:

  • Maintain detailed records of the complete genotype of all strains

  • Document the source and passage history of each strain

  • Sequence verify the YNR021W locus in each strain background

• Standardized experimental conditions:

  • Establish uniform growth conditions (media composition, temperature, culture volumes)

  • Standardize cell harvesting at specific growth phases (mid-log, early stationary)

  • Use identical extraction and analysis protocols across all strains

• Reference point normalization:

  • Include a common reference strain (e.g., S288C) in all experiments

  • Express results as relative changes compared to this reference

  • Use internal controls for normalization (housekeeping genes, constitutive markers)

• Genetic background effects analysis:

  • Systematically test epistatic interactions with key genetic differences between backgrounds

  • Consider backcrossing to create isogenic strains differing only in YNR021W

  • Use complementation studies to verify phenotype attribution

• Rigor enhancing practices:

  • Increase biological replicates (minimum of 3-5)

  • Implement blinding procedures when possible

  • Pre-register experimental designs and analysis plans