Recombinant Saccharomyces cerevisiae Genetic interactor of prohibitin 7, mitochondrial (GEP7)

What is GEP7 and what is its known function in Saccharomyces cerevisiae?

GEP7 (YGL057C) is a mitochondrial protein in Saccharomyces cerevisiae that functions as a genetic interactor of prohibitin (Phb1). While its precise molecular function remains largely uncharacterized, studies indicate it plays a critical role in mitochondrial function and integrity. The protein is 287 amino acids in length, with the mature form spanning amino acids 25-287 after import into mitochondria .

Methodologically, GEP7's function can be investigated through:

• Gene deletion studies (null mutants exhibit respiratory growth defects)

• Synthetic genetic array analysis (reveals synthetic interactions with prohibitin/phb1 and gem1)

• Protein-protein interaction analyses using co-immunoprecipitation or yeast two-hybrid assays

• High-throughput mitochondrial proteomics, which consistently detects authentic, non-tagged protein in highly purified mitochondria

The genetic interaction with prohibitins is particularly significant as these proteins form large complexes in the mitochondrial inner membrane that function as membrane-bound chaperones for stabilizing mitochondrial translation products .

What are the optimal methods for expressing and purifying recombinant GEP7 protein?

Expressing and purifying recombinant GEP7 protein requires careful optimization at multiple levels:

Expression systems and conditions:

• E. coli BL21(DE3) has been successfully used for expressing recombinant GEP7

• Expression with N-terminal His-tag facilitates single-step affinity purification

• Optimal expression typically occurs at lower temperatures (16-20°C) to enhance folding

• Induction with IPTG (for E. coli) or methanol (for P. pastoris) depending on the system used

Purification protocol:

• Cell lysis (sonication or detergent-based methods for membrane proteins)

• Affinity chromatography (Ni-NTA for His-tagged proteins)

• Size exclusion chromatography for final polishing

• Concentration using appropriate molecular weight cutoff filters

Buffer optimization:

• Tris/PBS-based buffer, pH 8.0

• Addition of 6% Trehalose as stabilizer

• For long-term storage: addition of glycerol (final concentration up to 50%)

Quality control metrics:

• SDS-PAGE should verify purity >90%

• Western blotting confirms identity

• Mass spectrometry for accurate mass determination

Specific parameters for GEP7 storage and handling:

• Store at -20°C/-80°C upon receipt

• Aliquot to avoid repeated freeze-thaw cycles

• Reconstitute lyophilized protein in deionized sterile water to 0.1-1.0 mg/mL

How can I validate the proper folding and activity of recombinant GEP7?

Validating proper folding and activity of recombinant GEP7 requires multiple complementary approaches:

Structural integrity assessment:

• Circular dichroism (CD) spectroscopy to verify secondary structure content

• Thermal shift assays to determine protein stability

• Size exclusion chromatography to confirm monomeric/oligomeric state

• Dynamic light scattering to assess homogeneity

Functional validation:

• In vitro binding assays with known interaction partners (e.g., Phb1)

• ATPase activity assays if enzymatic function is predicted

• Blue native PAGE to verify incorporation into native-like complexes

• Complementation assays in ΔGEP7 yeast strains

Microscopy-based validation:

• Localization studies using fluorescently-tagged GEP7 in yeast

• Co-localization with mitochondrial markers

• Rescue of mitochondrial morphology phenotypes in ΔGEP7 cells

Since the precise biochemical activity of GEP7 remains unknown, functional validation should include an assessment of its ability to restore respiratory growth in ΔGEP7 yeast strains when expressed from a plasmid. This serves as a crucial indicator that the recombinant protein retains its biological activity .

What phenotypic assays are most informative for studying GEP7 function?

When investigating GEP7 function, the following phenotypic assays provide the most valuable insights:

Growth and viability assays:

• Serial dilution spot tests on fermentable (glucose) vs. non-fermentable (glycerol, ethanol) carbon sources

• Growth curve analysis under respiratory conditions

• Competitive growth assays with wild-type strains

• Stress sensitivity profiling (oxidative stress, heat shock, osmotic stress)

Mitochondrial function assays:

• Oxygen consumption rate (OCR) measurements using oxygen electrodes or plate-based systems

• Mitochondrial membrane potential assessment using fluorescent dyes (TMRM, JC-1)

• ATP production quantification under respiratory conditions

• ROS production measurement using specific dyes or sensors

Mitochondrial morphology analysis:

• Fluorescence microscopy using matrix-targeted fluorescent proteins

• Quantitative analysis of network parameters (fragmentation, branching)

• Electron microscopy for ultrastructural examination

• Time-lapse imaging to capture dynamic morphological changes

Genetic interaction profiling:

• Synthetic genetic array analysis with mitochondrial function genes

• Epistasis analysis with prohibitin complex components

• Multi-gene deletion studies to assess pathway relationships

• Suppressor screens to identify functional connections

The respiratory growth defect in ΔGEP7 strains is particularly informative, indicating that GEP7 likely plays a role in maintaining proper mitochondrial function under conditions that require oxidative phosphorylation .

How can I design experiments to study the interaction between GEP7 and prohibitins?

Designing experiments to characterize the GEP7-prohibitin interaction requires a multi-faceted approach:

Genetic interaction studies:

• Create single and double knockout strains (ΔGEP7, ΔPhb1, and ΔGEP7ΔPhb1)

• Perform growth phenotype analysis under various conditions

• Employ epistasis analysis to determine functional relationships

• Use complementation studies with domain-specific mutants

Physical interaction analysis:

• Co-immunoprecipitation with tagged versions of GEP7 and Phb1

• Proximity labeling techniques (BioID, APEX) for in vivo detection

• Fluorescence resonance energy transfer (FRET) for direct interaction assessment

• In vitro binding assays using purified components

Functional assays:

• Mitochondrial membrane potential analysis in single vs. double mutants

• Protein stability assays for mitochondrially encoded proteins

• Respiratory capacity measurements across mutant strains

• mtDNA stability and maintenance assessment

Structural studies:

• Cross-linking mass spectrometry to map interaction interfaces

• Mutational analysis to identify critical binding regions

• Hydrogen-deuterium exchange mass spectrometry to detect conformational changes

• Cryo-EM of reconstituted complexes

The synthetic growth defect observed in ΔGEP7ΔPhb1 double mutants suggests that these proteins function in parallel or complementary pathways. Understanding this relationship is critical, as prohibitins form large complexes in the mitochondrial inner membrane that act as membrane-bound chaperones for stabilizing mitochondrial translation products .

How does GEP7 contribute to mitochondrial membrane organization and potential mtDNA maintenance?

Investigating GEP7's role in mitochondrial membrane organization and mtDNA maintenance requires sophisticated experimental approaches:

Membrane organization studies:

• Blue native PAGE to identify membrane protein complexes

• Lipidomic analysis to detect altered membrane composition

• Detergent resistance assays to identify membrane microdomain association

• Atomic force microscopy to examine membrane properties

mtDNA analysis techniques:

• qPCR-based measurement of mtDNA copy number

• Long-range PCR to detect large-scale deletions

• Next-generation sequencing for comprehensive mutation analysis

• Super-resolution microscopy of nucleoids using DNA-binding fluorescent proteins

Prohibitin-related pathways:
Recent research has shown that Prohibitin 1 (PHB1) regulates mtDNA release and downstream inflammatory responses . Studies demonstrated that:

• Knockdown of PHB1 increases cytoplasmic mtDNA levels

• This effect is dependent on SPG7 and AFG3L2, components of the m-AAA protease complex

• Additional knockdown of SPG7 or AFG3L2 restores the co-localization between mtDNA and mitochondria in PHB1-depleted cells

Given GEP7's synthetic interaction with prohibitin, it may play a role in similar pathways affecting mtDNA stability and localization. The study by Wang et al. revealed that knocking down PHB1 increases production of cleaved IL-1β, which is repressed when SPG7 or AFG3L2 are additionally knocked down . Investigation of similar pathways in GEP7-deficient cells could provide insights into its function.

What computational approaches can predict GEP7's function based on evolutionary relationships?

Advanced computational approaches provide valuable insights into GEP7's potential functions:

Sequence-based function prediction:

• Profile Hidden Markov Models for remote homology detection

• Position-Specific Scoring Matrices to identify conserved motifs

• Genomic context analysis to identify conserved gene neighborhoods

• Machine learning approaches incorporating multiple sequence features

Network-based approaches:

• Analysis of protein-protein interaction networks from STRING database

• Co-expression network analysis across multiple conditions

• Functional association networks to identify pathway connections

• Module detection and enrichment analysis

According to STRING database analysis, GEP7 has predicted functional partners including:

Structural bioinformatics:

• AlphaFold2 or RoseTTAFold for 3D structure prediction

• Structure-based function prediction via fold recognition

• Molecular dynamics simulations to explore conformational dynamics

• Protein-protein docking with known interactors

Phylogenetic analysis:

• Presence/absence patterns across diverse species

• Identification of co-evolving gene families

• Detection of selection signatures

• Correlation with phenotypic traits across fungal species

These computational predictions, combined with GEP7's experimental synthetic interactions with PHB1 and GEM1, suggest involvement in mitochondrial membrane organization, protein quality control, or organelle communication pathways .

How can multi-omics approaches be integrated to comprehensively characterize GEP7's function?

Integrating multiple omics technologies provides a systems-level understanding of GEP7's function:

Transcriptomics approaches:

• RNA-seq of wild-type vs. ΔGEP7 strains under various conditions

• Time-course analysis during metabolic shifts (fermentation to respiration)

• Differential expression analysis to identify affected pathways

• Integration with transcription factor binding data

Proteomics strategies:

• Quantitative proteomics using TMT or SILAC labeling

• Post-translational modification profiling

• Protein turnover rate determination with pulse-chase labeling

• Complexome profiling to identify altered protein complexes

Metabolomics analysis:

• Untargeted metabolomics to identify altered metabolite profiles

• Flux analysis using 13C-labeled substrates

• Lipidomics to detect membrane composition changes

• Focus on TCA cycle intermediates and respiratory metabolism

Integration methodologies:

• Pathway enrichment analysis across multiple datasets

• Network reconstruction using multi-omics data

• Causal network inference to identify regulatory relationships

• Machine learning approaches for pattern recognition

A comparable multi-omics study conducted on gene expression profiles (GEP) in myelodysplastic syndrome mice models successfully identified novel dysregulated pathways . This study validated findings through:

• Comparison between microarray data and RT-PCR results

• Concordance between different tissue types (spleen and bone marrow)

• Validation in patient samples

Key pathways identified included signal transduction, oxidative metabolism, and DNA processing, demonstrating how GEP analysis can connect molecular alterations to functional outcomes . Similar approaches applied to GEP7 could reveal its position within mitochondrial functional networks and identify affected pathways in mutant strains.

What are the best approaches for studying GEP7's role in mitochondrial calcium homeostasis?

Given the potential relationship between GEP7 and mitochondrial calcium dynamics, the following approaches are recommended:

Calcium imaging techniques:

• Use of genetically encoded calcium indicators targeted to mitochondria (mito-GCaMP)

• Ratiometric dyes for quantitative calcium measurements (Fura-2, Indo-1)

• High-speed imaging to capture rapid calcium transients

• Simultaneous cytosolic and mitochondrial calcium monitoring

Calcium flux measurements:

• 45Ca2+ uptake assays in isolated mitochondria

• Calcium retention capacity assessment

• Ruthenium red-sensitive vs. insensitive uptake pathways

• Measurement of calcium-dependent changes in oxygen consumption

ER-mitochondria contact site analysis:

• Quantification of contact sites in wild-type vs. ΔGEP7 strains

• In situ proximity ligation assay to detect protein interactions at contacts

• Assessment of calcium transfer efficiency at these sites

• Analysis of GEM1 function at these contacts in absence of GEP7

Recent research has shown that in PHB1-depleted cells, there is a disorder in mitochondrial Ca2+ uptake, which is recovered by knockdown of SPG7 or AFG3L2 . This connection is particularly relevant given that:

• GEP7 has a synthetic interaction with prohibitin (PHB1)

• Prohibitins regulate mitochondrial calcium uptake

• This regulation appears to involve the m-AAA protease complex (SPG7/AFG3L2)

Experimental designs should compare calcium dynamics in:

• Wild-type cells

• ΔGEP7 cells

• ΔPhb1 cells

• ΔGEP7ΔPhb1 double mutants

This approach will help determine whether GEP7 functions in the same pathway as prohibitins with respect to calcium regulation or represents a parallel regulatory mechanism .

How can I establish an inducible expression system for GEP7 in mammalian cells?

For inducible expression of GEP7 in mammalian cells, the T7 RNA polymerase-mediated expression system offers significant advantages:

Vector construction strategy:

• Clone the T7 RNA polymerase gene into a mammalian expression vector (e.g., modified pIRES2-EGFP plasmid)

• Create a separate vector containing:

  • T7 promoter

  • IRES sequence

  • GEP7 gene

  • Poly A signal

Components required:

• BL-21 genome as template for T7 RNA polymerase gene amplification

• PCR primers with appropriate restriction sites

• pUC57 plasmid for cloning T7-responsive elements

• Mammalian cell culture reagents (DMEM, FBS, antibiotics)

Transfection and expression:

• Co-transfect both plasmids into HEK-293 cells

• Alternatively, use T7-BHK cells that stably express T7 RNA polymerase

• Validate expression using Western blotting and fluorescence microscopy

• Optimize induction conditions if using an inducible promoter

This system has been shown to be highly efficient for expression of foreign genes in mammalian cell lines . For GEP7 specifically, consider adding a mitochondrial targeting sequence to ensure proper localization, and include either a His-tag or fluorescent protein tag for detection and purification.

For temporal control, this system can be combined with tetracycline-inducible elements, allowing precise regulation of expression timing.

What approaches can be used to study prohibitin-GEP7 interactions in human cell models?

Studying prohibitin-GEP7 interactions in human cells requires careful experimental design:

Expression systems:

• Clone both yeast GEP7 and human prohibitins into appropriate mammalian vectors

• Add mitochondrial targeting sequences if needed to ensure proper localization

• Use inducible expression systems for temporal control

• Consider stable cell lines for long-term studies

Interaction detection methods:

• Co-immunoprecipitation with tagged versions of both proteins

• Proximity labeling techniques (BioID, APEX) for in vivo interaction detection

• Split-GFP or FRET-based sensors for direct visualization

• Cross-linking mass spectrometry to map interaction interfaces

Functional assays:

• Assess mitochondrial morphology using fluorescence microscopy

• Measure respiratory function using oxygen consumption rate analysis

• Evaluate mitochondrial membrane potential using fluorescent dyes

• Analyze mtDNA stability and copy number

Gene editing approaches:

• CRISPR/Cas9-mediated knockout of prohibitins

• Expression of yeast GEP7 in prohibitin-deficient cells

• Complementation studies with specific domains or mutants

• Creation of reporter cell lines for high-throughput screening

Research has shown that human prohibitin and BAP37 form a high molecular weight complex very similar to the yeast Phb1/2 complex . This conservation suggests that yeast GEP7 might interact with human prohibitins when expressed in human cells. The stabilization of mitochondrial translation products by the Phb1/2 complex does not result from direct inhibition of the Afg3p/Rca1p protease complex but from protection through direct binding of translation products .

This mechanistic insight should guide experimental designs when studying potential GEP7-prohibitin interactions in human cells, focusing on translation product stability and protease protection assays.

How can GEP7 be incorporated into genomics education partnership (GEP) research projects?

GEP7 offers an excellent model for student research projects within the Genomics Education Partnership framework:

Research project structure:

• Gene annotation and comparative genomics studies across fungal species

• Construction of gene models using evidence tracks on genome browsers

• Analysis of conserved features versus evolutionary changes

• Integration with larger research questions about mitochondrial function

Methodological approach:

• Students evaluate multiple lines of evidence (sequence similarity, gene predictions, RNA-Seq data)

• Resolution of differences among evidence tracks to create defendable gene models

• Quality control through independent annotation by multiple students

• Data assembly for meta-analysis and potential publication

Specific GEP7-focused projects:

• Annotation of GEP7 homologs in related yeast species

• Comparative analysis of regulatory regions

• Identification of conserved motifs and domains

• Integration with data on prohibitin family proteins

The GEP introduces students to research in genomics by engaging them in projects where careful annotation provides important data. With GEP7, students can contribute to understanding an important mitochondrial protein while developing bioinformatics skills .

For quality control, each project is completed by at least two students working independently, then reconciled by experienced students. The assembled data can be used for meta-analysis, with contributing faculty and students eligible for co-authorship on resulting publications .