Recombinant Yarrowia lipolytica Translocation protein SEC62 (SEC62)

What is the basic structure and function of Yarrowia lipolytica SEC62?

Yarrowia lipolytica SEC62 is a 396 amino acid protein with two potential transmembrane domains that functions as an integral membrane protein. The protein features N- and C-termini facing the cytosol with the N-terminus containing a cluster of basic amino acids . As shown by Western blotting analysis, Y. lipolytica Sec62p behaves as an integral membrane protein .

SEC62 is a component of the protein translocation machinery of the endoplasmic reticulum (ER) membrane, specifically associated with the Sec61 complex, which is the central component of the protein translocation apparatus . The Sec61-Sec62-Sec63 complex is involved in post-translational protein translocation into the ER and may also perform backward transport of ER proteins subject to ubiquitin-proteasome-dependent degradation .

What are the recommended expression systems for recombinant Y. lipolytica SEC62?

E. coli is the most commonly used expression system for recombinant Y. lipolytica SEC62, as demonstrated in multiple studies . For optimal expression, the full-length protein (1-396 amino acids) can be fused to an N-terminal His tag to facilitate purification . The recombinant protein is typically expressed in E. coli and can be purified to greater than 90% purity as determined by SDS-PAGE .

Alternative expression systems include yeast, baculovirus, and mammalian cell systems, which may be more suitable for studies requiring post-translational modifications or specific protein folding , though E. coli remains the most straightforward system for basic structural and functional studies.

What purification protocols yield the highest purity and functionality for recombinant Y. lipolytica SEC62?

For high-purity recombinant Y. lipolytica SEC62, a purification protocol using His-tag affinity chromatography is recommended. The protocol typically involves:

• Expression in E. coli with an N-terminal His tag

• Cell lysis under native or denaturing conditions

• Affinity purification using Ni-NTA resin

• Elution with imidazole-containing buffer

• Buffer exchange or dialysis to remove imidazole

• Optional additional purification steps (ion exchange, size exclusion)

The resulting protein should have greater than 90% purity as determined by SDS-PAGE . For storage, the protein is typically lyophilized or stored in Tris/PBS-based buffer with 6% trehalose at pH 8.0 . To maintain functionality, it's recommended to avoid repeated freeze-thaw cycles by aliquoting the protein and storing at -20°C/-80°C, with working aliquots kept at 4°C for up to one week .

How should recombinant Y. lipolytica SEC62 be reconstituted and stored for optimal stability?

For optimal stability and functionality, recombinant Y. lipolytica SEC62 should be reconstituted and stored as follows:

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

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

• Add glycerol to a final concentration of 5-50% (recommended: 50%)

• Aliquot for long-term storage at -20°C/-80°C

• Avoid repeated freeze-thaw cycles

• Store working aliquots at 4°C for up to one week

For storage buffer, a Tris/PBS-based buffer with 6% trehalose at pH 8.0 is recommended .

How can researchers employ SEC62 in protein translocation studies?

Researchers can use recombinant Y. lipolytica SEC62 for multiple experimental approaches to study protein translocation:

• In vitro translocation assays: Purified recombinant SEC62 can be reconstituted with other components of the translocation machinery (SEC61, SEC63) in liposomes to study its role in post-translational protein import into the ER.

• Signal sequence specificity analysis: SEC62 plays a role in regulating membrane topogenesis of moderately hydrophobic signal anchor proteins . Researchers can use mutational analysis and in vitro translocation assays to determine the specificity of SEC62 for different signal sequences.

• Complementation studies: The functional conservation of SEC62 across species can be tested through complementation assays where Y. lipolytica SEC62 is expressed in S. cerevisiae sec62 mutant strains .

• Protein-protein interaction studies: SEC62's interactions with other components of the translocation machinery can be studied using pull-down assays, co-immunoprecipitation, or crosslinking approaches.

The choice of methodology depends on the specific research question, with in vitro reconstitution systems providing insights into mechanistic details and in vivo complementation studies revealing functional conservation.

What techniques are most effective for studying SEC62's transmembrane topology?

To study SEC62's transmembrane topology, researchers can employ several complementary techniques:

• Protease protection assays: By treating SEC62-containing membranes with proteases in the presence or absence of detergents, researchers can determine which portions of the protein are accessible from the cytoplasmic side.

• Glycosylation mapping: Introduction of artificial glycosylation sites at various positions in the protein sequence can reveal which domains reside in the ER lumen (and can therefore be glycosylated).

• Cysteine accessibility methods: Substituting specific residues with cysteines and then testing their accessibility to membrane-impermeable sulfhydryl reagents can map the topology.

• Fluorescence resonance energy transfer (FRET): By attaching fluorescent probes to different domains of SEC62, researchers can determine their proximity relationships.

• Cryo-electron microscopy: For structural studies, cryo-EM can provide insights into the three-dimensional arrangement of SEC62 within the membrane.

For Y. lipolytica SEC62 specifically, studies have confirmed it has two transmembrane domains with both N- and C-termini facing the cytosol .

What methodological approaches can detect SEC62's interactions with other components of the translocation machinery?

Several methodological approaches can effectively detect and characterize SEC62's interactions with other translocation machinery components:

• Co-immunoprecipitation (Co-IP): Using antibodies against SEC62 to pull down associated proteins like SEC61 and SEC63, followed by Western blotting or mass spectrometry.

• GST pull-down assays: Recombinant GST-tagged SEC62 can be used to identify binding partners from cell lysates.

• Bimolecular Fluorescence Complementation (BiFC): By fusing SEC62 and potential interaction partners with complementary fragments of a fluorescent protein, interaction can be visualized in living cells.

• Surface Plasmon Resonance (SPR): Purified recombinant SEC62 can be immobilized on a sensor chip to measure binding kinetics with other purified components.

• Crosslinking followed by mass spectrometry: Chemical crosslinkers can capture transient interactions, and mass spectrometry can identify the crosslinked peptides.

• Yeast two-hybrid screening: Although this has limitations for membrane proteins, modified versions such as split-ubiquitin systems can be effective.

Research has shown that SEC62 associates with the ribosome-free SEC61 complex and SEC63 , and that the cytosolic N-terminus of SEC62 is important for interaction with SEC63 .

How do researchers compare functional conservation of SEC62 across yeast species using complementation assays?

Researchers use complementation assays to compare functional conservation of SEC62 across yeast species by following these methodological steps:

• Generation of recipient strain: Create a S. cerevisiae strain with a temperature-sensitive or null mutation in the endogenous SEC62 gene.

• Cloning of heterologous SEC62: Clone the SEC62 gene from the species of interest (e.g., Y. lipolytica) into a suitable yeast expression vector.

• Transformation: Transform the recipient S. cerevisiae strain with the expression vector containing the heterologous SEC62.

• Phenotypic assessment: Test for complementation by assessing growth at the non-permissive temperature or other relevant phenotypes.

• Quantitative analysis: Measure the degree of complementation by growth rate analysis, protein secretion efficiency, or other quantitative assays.

Studies have demonstrated that Y. lipolytica SEC62 cDNA is able to complement a S. cerevisiae sec62 null mutant strain, confirming functional conservation despite only 53.6% amino acid similarity between the two proteins . This approach allows researchers to determine which domains and residues are critical for function across species.

What experimental approaches can distinguish between SRP-dependent and SEC62-dependent protein translocation?

To distinguish between SRP-dependent and SEC62-dependent protein translocation pathways, researchers can employ the following experimental approaches:

• In vitro translation-translocation assays: Using cell-free translation systems with or without SRP, researchers can determine whether the translocation of specific proteins is SRP-dependent or SRP-independent.

• Genetic approaches: Using yeast strains with mutations in components of either the SRP pathway or the SEC62 pathway, researchers can identify which pathway is required for specific substrate proteins.

• Substrate analysis with controlled hydrophobicity: Creating model proteins with signal sequences or signal anchor sequences of controlled hydrophobicity can help determine the hydrophobicity-dependent targeting efficiency and pathway preference .

• Ribosome-binding assays: Since SRP-dependent translocation involves co-translational targeting, assessing ribosome binding to SEC62 can provide insights into pathway integration.

• Temporal analysis of translocation: Pulse-chase experiments can distinguish between co-translational (typically SRP-dependent) and post-translational (typically SEC62-dependent) translocation.

Research has shown that SRP-dependent co-translational and SRP-independent post-translational translocation are not mutually exclusive for signal anchor proteins, and moderately hydrophobic ones require both SRP and Sec62 for proper targeting and translocation to the ER .

How can researchers investigate the role of Y. lipolytica SEC62 in metabolism and cellular detoxification?

Researchers investigating Y. lipolytica SEC62's role in metabolism and cellular detoxification can employ these methodological approaches:

• Generation of SEC62 overexpression and knockdown strains: Create Y. lipolytica strains with modulated SEC62 expression levels to study phenotypic changes.

• Metabolic profiling: Use metabolomics to analyze changes in cellular metabolites when SEC62 expression is altered.

• Transcriptomic analysis: Employ RNA-seq to identify genes whose expression changes in response to SEC62 modulation, particularly those involved in metabolism and detoxification pathways.

• Stress response assays: Subject SEC62-modified strains to various stressors (oxidative, toxic compounds) to assess their detoxification capabilities.

• Protein secretion analysis: Evaluate the secretion efficiency of detoxification enzymes in strains with altered SEC62 expression.

• In vivo detoxification assays: Test the ability of SEC62-modified strains to detoxify specific compounds like cyanogenic glycosides.

Recent research has shown Y. lipolytica strains can be engineered for efficient detoxification of multiple cyanogenic glycosides from edible plants . While the study specifically mentioned SEC61β overexpression to stimulate the signal recognition particle, the interconnected role of SEC62 in this process could be investigated using similar approaches .

What techniques can elucidate SEC62's role in ER stress and unfolded protein response recovery?

To elucidate SEC62's role in ER stress and unfolded protein response (UPR) recovery, researchers can employ these specialized techniques:

• ER stress induction followed by recovery monitoring: Treat cells with ER stress inducers (tunicamycin, thapsigargin) and monitor recovery in the presence/absence of SEC62.

• Fluorescent-tagged SEC62 visualization: Track SEC62 localization during ER stress and recovery using confocal microscopy.

• ER-phagy assays: Monitor autophagic degradation of ER components using fluorescent markers for autophagosomes and ER.

• UPR reporter systems: Use reporter constructs driven by UPR-responsive elements to quantify UPR activation.

• Protein-protein interaction during stress recovery: Employ techniques like proximity labeling or FRET to identify stress-specific interactions.

• Calcium flux measurements: Monitor ER calcium homeostasis during stress and recovery.

Research has shown that SEC62 can facilitate the elimination of excess ER and accumulated misfolded proteins via autophagy (ER-phagy or recov-ER-phagy) in response to ER stress . SEC62 has been implicated in UPR recovery through the PERK/ATF4 pathway and binding to LC3II , suggesting complex roles in maintaining ER homeostasis during stress conditions.

How can researchers explore the evolutionary gain of function of SEC62 from yeast to humans using Y. lipolytica as a model?

To explore the evolutionary gain of function of SEC62 from yeast to humans using Y. lipolytica as a model system, researchers can employ these methodological approaches:

• Comparative sequence analysis: Align SEC62 sequences from diverse species including Y. lipolytica, S. cerevisiae, and humans to identify conserved and divergent regions.

• Domain swapping experiments: Create chimeric proteins containing domains from different species' SEC62 to identify which regions confer specific functions.

• Heterologous expression and complementation: Express human SEC62 in Y. lipolytica sec62 mutants to test for functional conservation and gain of function.

• Ribosome binding assays: Test the ability of SEC62 from different species to interact with ribosomes, as this is a function gained in vertebrate SEC62.

• Structure-function analysis: Use site-directed mutagenesis to modify specific residues in the basic oligopeptide motifs that are present in human SEC62 but absent in yeast SEC62.

Research has demonstrated that in the course of evolution, SEC62 of vertebrates has gained the additional function of interacting with ribosomes. Two basic oligopeptide motifs are responsible for this interaction and are absent from yeast SEC62 as well as from SEC62 in invertebrates or plants . Y. lipolytica, positioned between simple yeasts and higher eukaryotes, provides an excellent model to study this evolutionary progression.

How can recombinant Y. lipolytica SEC62 be used in cancer research studies?

Recombinant Y. lipolytica SEC62 can serve as a valuable tool in cancer research through these methodological approaches:

• Comparative studies: Comparing the structure and function of Y. lipolytica SEC62 with human SEC62 can provide insights into conserved mechanisms potentially relevant to cancer.

• Antibody development and validation: Using recombinant Y. lipolytica SEC62 to generate and validate antibodies that can later be used in cancer studies.

• Structural biology approaches: Using the yeast protein as a model for structural studies that can inform the design of inhibitors targeting human SEC62 in cancer.

• Evolution-guided discovery: Identifying functional differences between yeast and human SEC62 that might contribute to cancer-promoting activities in humans.

• Drug screening platforms: Using Y. lipolytica SEC62-based assays as initial screens for compounds that might later be optimized to target human SEC62 in cancer.

Research has established human SEC62 as a potential biomarker and therapeutic target in various cancers, including hepatocellular carcinoma, gastric cancer, and colorectal cancer . Studies have shown that SEC62 promotes cancer cell migration, invasion, and chemoresistance through various pathways including integrinα/CAV1 signaling and Wnt/β-catenin activation . While direct applications of Y. lipolytica SEC62 in cancer research are emerging, the evolutionary conservation of key domains makes it a valuable model for understanding fundamental mechanisms.

What methodological approaches can determine if mechanisms of SEC62's cancer-promoting effects are conserved in yeast?

To determine if mechanisms of SEC62's cancer-promoting effects are conserved in yeast, researchers can employ these methodological approaches:

• Pathway conservation analysis: Compare signaling pathways affected by SEC62 in cancer cells with homologous pathways in yeast, focusing on:

  • Cell migration/invasion equivalents (pseudohyphal growth in yeast)

  • Cell cycle regulation

  • Stress response pathways

  • Protein quality control mechanisms

• Domain-specific functional assays: Identify domains in human SEC62 critical for cancer promotion and test if homologous domains in yeast SEC62 have similar functions.

• Heterologous expression systems: Express human SEC62 in yeast and assess phenotypic changes related to cancer-like behaviors (increased growth rate, stress resistance).

• Genetic interaction screens: Perform synthetic genetic array analysis in yeast with SEC62 mutations to identify genetic interactions potentially relevant to cancer biology.

• Protein-protein interaction mapping: Compare the interactome of SEC62 in yeast versus cancer cells to identify conserved interaction partners.

Research has shown that SEC62 promotes cancer through various mechanisms including activation of autophagy , interaction with the Wnt/β-catenin pathway , and activation of integrinα/CAV1 signaling . While these specific cancer-promoting mechanisms may not be directly conserved in yeast, the fundamental roles of SEC62 in protein translocation, ER homeostasis, and stress response likely represent evolutionarily conserved functions that can provide insights into its cancer-relevant activities.

How can researchers accurately quantify SEC62 expression in Y. lipolytica under various experimental conditions?

Researchers can accurately quantify SEC62 expression in Y. lipolytica under various experimental conditions using these methodological approaches:

• RT-qPCR with appropriate reference genes: Use validated reference genes for Y. lipolytica such as TEF1, TPI1, UBC2, SRPN2, ALG9-like, and RYL1, which have been shown to be unaffected by the burden of heterologous protein overexpression .

• Absolute quantification: Develop standard curves using known concentrations of recombinant SEC62 cDNA for absolute quantification of transcript levels.

• Multiple reference gene normalization: Use computational tools like geNorm and NormFinder to select the most stable combination of reference genes for specific experimental conditions .

• Western blotting with appropriate controls: Quantify SEC62 protein levels using calibrated Western blotting with recombinant SEC62 protein standards.

• Fluorescent protein tagging: Generate SEC62-fluorescent protein fusions for live-cell quantification of expression and localization.

Research has shown that SEC62 itself is not a suitable reference gene for normalization of RT-qPCR data in Y. lipolytica, as it was identified as one of the least stable genes across various conditions . Instead, researchers should use validated reference genes like those mentioned above, depending on the specific experimental conditions.

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What approaches can resolve contradictory findings in SEC62 functional studies between different yeast species?

To resolve contradictory findings in SEC62 functional studies between different yeast species, researchers can employ these methodological approaches:

• Standardized experimental conditions: Use identical growth conditions, expression systems, and assay methods when comparing SEC62 function across species.

• Direct comparative studies: Conduct side-by-side experiments with SEC62 from multiple species in the same experimental setting rather than comparing results across different studies.

• Chimeric protein analysis: Create chimeric proteins with domains from different species' SEC62 to identify which regions contribute to species-specific functions.

• Heterologous complementation with quantitative readouts: Express SEC62 from different species in a common host with SEC62 deletion and quantitatively measure the degree of complementation.

• Evolutionary context analysis: Consider the evolutionary distance between species and the potential adaptation of SEC62 to species-specific cellular environments.

• Structure-function correlation: Correlate specific amino acid differences with functional differences through systematic mutagenesis.

While the search results don't explicitly mention contradictory findings, they do highlight the functional conservation of SEC62 despite only 53.6% amino acid similarity between Y. lipolytica and S. cerevisiae , as well as evolutionary gain of function in vertebrate SEC62 compared to yeast . These observations suggest that while core functions are conserved, species-specific adaptations and additional functions have evolved, which could potentially lead to seemingly contradictory experimental outcomes.

How can researchers harness SEC62's function to improve heterologous protein secretion in Y. lipolytica?

Researchers can harness SEC62's function to improve heterologous protein secretion in Y. lipolytica through these methodological approaches:

• Optimized SEC62 expression levels: Fine-tune SEC62 expression to match the increased demand for protein translocation without causing ER stress. This can be achieved through:

  • Promoter selection for appropriate expression levels

  • Copy number optimization

  • Inducible expression systems

• Co-expression with synergistic factors: Combine SEC62 optimization with other components of the secretory pathway:

  • SEC61 complex components

  • SEC63 (which forms a functional complex with SEC62)

  • Signal recognition particle (SRP) components

  • ER chaperones like BiP/Kar2p

• Signal sequence engineering: Design signal sequences optimized for SEC62-dependent translocation based on hydrophobicity profiles and amino acid composition.

• Strain engineering approaches:

  • CRISPR/Cas9-mediated genomic integration of optimized SEC62

  • Deletion of competing secretory pathway components

  • Adaptive laboratory evolution to select for improved secretion

Recent research demonstrated that overexpression of protein translocation proteins, including SEC61β and SEC62, stimulated the signal recognition particle (SRP) pathway and improved protein expression in Y. lipolytica . Additionally, researchers found that such engineered strains upregulated ribosome biogenesis, the sec-dependent protein export pathway, and the sulfur relay system to facilitate production and transmembrane efflux of secreted proteins .

What experimental design would best evaluate the potential of SEC62-modified Y. lipolytica strains for biotechnological applications?

An optimal experimental design to evaluate the potential of SEC62-modified Y. lipolytica strains for biotechnological applications would include:

• Strain construction and verification:

  • Generate strains with SEC62 overexpression, knockdown, and wild-type controls

  • Create strains with various SEC62 expression levels using different promoters

  • Verify SEC62 expression levels by RT-qPCR and Western blotting

  • Confirm proper localization using fluorescent tagging or subcellular fractionation

• Protein secretion performance assessment:

  • Express a panel of model proteins with different characteristics (size, hydrophobicity, glycosylation)

  • Quantify secretion efficiency using enzyme activity assays, SDS-PAGE, and Western blotting

  • Assess protein quality through activity assays and structure analysis

  • Measure secretion kinetics through pulse-chase experiments

• Bioprocess performance evaluation:

  • Batch and fed-batch fermentation to evaluate growth kinetics and protein production

  • Scale-up studies from shake flask to bioreactor

  • Productivity and yield calculations for economic feasibility assessment

  • Process stability evaluation through multiple generations

• Stress response characterization:

  • Evaluate ER stress markers (e.g., UPR activation)

  • Assess cell viability under production conditions

  • Measure metabolic burden through growth rate analysis

  • Test robustness under various media compositions and culture conditions

• Omics-based analysis:

  • Transcriptomics to identify global changes in gene expression

  • Proteomics to assess changes in cellular protein composition

  • Metabolomics to identify metabolic shifts

  • Systems biology integration of multi-omics data

• Application-specific testing:

  • For food applications: safety assessment, sensory evaluation, nutritional analysis

  • For industrial enzymes: specific activity, stability, substrate specificity

  • For pharmaceutical proteins: biological activity, immunogenicity, stability