Recombinant Schizosaccharomyces pombe Transmembrane GTPase fzo1 (fzo1)
Description
Physical and Biochemical Properties
The fzo1 protein belongs to the dynamin-related GTPase protein (DRP) family, which are key players in membrane remodeling processes . As a mitofusin, fzo1 is specifically localized to the outer mitochondrial membrane, as confirmed through fluorescence microscopy studies . Its structural characteristics include the following notable features:
| Property | Description |
|---|---|
| Molecular Classification | Dynamin-related GTPase protein (DRP) |
| Subcellular Localization | Outer mitochondrial membrane |
| Key Functional Domains | GTPase domain with P-loop and switch motifs |
| Storage Buffer | Tris/PBS-based buffer, 6% Trehalose, pH 8.0 |
| Recommended Reconstitution | Deionized sterile water to 0.1-1.0 mg/mL with 5-50% glycerol |
The GTPase domain of fzo1 contains critical P-loop (GxxxxGK[S/T]) and switch motifs that are essential for its function. Specific residues within these regions, including D195, N197, K200, S201, T221, and D320, have been identified as crucial for the protein's activity .
Role in Mitochondrial Fusion
The fzo1 protein serves as a mediator of mitochondrial fusion in Schizosaccharomyces pombe, representing the first characterized mitofusin in this organism . Similar to its homologue in Saccharomyces cerevisiae, fzo1 plays an essential role in maintaining mitochondrial morphology and function through facilitating the fusion of mitochondrial outer membranes .
Mitochondrial fusion is a critical process for maintaining functional mitochondria, allowing for the exchange of contents between mitochondria, complementation of damaged mitochondrial DNA, and the formation of interconnected mitochondrial networks. Research indicates that fzo1-mediated mitochondrial fusion involves a multi-step process requiring GTP binding and hydrolysis, as well as interactions with other regulatory proteins .
Mechanistic Pathway of Fzo1-Mediated Fusion
Studies have elucidated distinct steps in the fzo1-mediated mitochondrial outer membrane fusion cycle:
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Homo-dimerization: Fzo1 assembles into homo-dimers, a process dependent on GTP binding to fzo1 and the presence of the protein Ugo1 .
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Trans-association: Upon formation of mitochondrial contacts, fzo1 homo-dimers further associate, allowing for membrane tethering between adjacent mitochondria .
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GTP Hydrolysis: Subsequent hydrolysis of GTP by fzo1 is required for its ubiquitylation by the F-box protein Mdm30 .
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Protein Degradation: Finally, Mdm30-dependent degradation of fzo1 completes its function in outer membrane fusion .
This sequential mechanism highlights how fzo1's GTPase activity couples with protein-protein interactions to drive the mitochondrial fusion process. Unlike other cellular membrane fusion events that involve protein recycling, mitofusins appear to operate through a non-cycling mechanism where protein degradation is an integral part of the fusion process .
Impact of Fzo1 Deletion
Disruption of the fzo1 gene in S. pombe results in distinct phenotypic changes that highlight its importance in mitochondrial function:
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Mitochondrial Morphology: Δfzo1 cells exhibit fragmented mitochondrial morphology, reflecting an imbalance in mitochondrial dynamics tilted toward excessive fission .
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Respiratory Function: Fzo1-deficient cells show dramatically reduced growth on glycerol medium, indicating compromised respiratory function .
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Mitochondrial DNA: The respiratory deficiency observed in Δfzo1 cells is consistent with the loss of mitochondrial DNA, as has been documented in other yeast models lacking functional mitofusins .
These phenotypic observations underscore the essential role of fzo1 in maintaining mitochondrial integrity and function through balanced fusion-fission dynamics.
Genetic Interactions with Dnm1
One of the most significant findings regarding fzo1 function comes from genetic interaction studies with dnm1, a protein involved in mitochondrial division. Research has revealed that:
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Phenotypic Rescue: Deletion of the dnm1 gene blocks mitochondrial fragmentation in Δfzo1 cells .
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Functional Recovery: Furthermore, dnm1 mutations rescue the respiratory growth defect observed in Δfzo1 single mutant cells .
These observations provide compelling evidence for a genetic interaction between fzo1 and dnm1, suggesting that a balance between division (mediated by dnm1) and fusion (mediated by fzo1) controls mitochondrial shape and function in S. pombe .
| Genotype | Mitochondrial Morphology | Respiratory Growth |
|---|---|---|
| Wild-type | Normal, tubular network | Normal |
| Δfzo1 | Fragmented | Severely impaired |
| Δdnm1 | Hyperconnected, aggregated | Normal |
| Δfzo1Δdnm1 | Rescued from fragmentation | Rescued |
GTP Binding and Hydrolysis
The GTPase activity of fzo1 is central to its function in mitochondrial fusion, with distinct roles for GTP binding and hydrolysis:
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GTP Binding: Essential for fzo1 dimerization, as demonstrated by mutations in the P-loop (D195A, K200A, S201N) that impair assembly into dimers .
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GTP Hydrolysis: Required for subsequent steps after dimerization and trans tethering, as shown by mutations in the switch regions (T221A, D320A) that do not affect dimerization but block fusion .
Experimental evidence from sucrose gradient centrifugation, crosslinking experiments, and blue native PAGE analyses has confirmed that fzo1 dimerization relies on GTP binding but does not require GTP hydrolysis .
Protein Interactions and Degradation
The activity of fzo1 is further regulated through interactions with other proteins, particularly Ugo1 and Mdm30:
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Ugo1 Interaction: Ugo1 is required for fzo1 dimerization, although this requirement can be bypassed by the addition of GTP in vitro .
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Mdm30 Regulation: Mdm30, an F-box protein, is responsible for fzo1 turnover in growing cells, which is required to maintain fusion-competent mitochondria .
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Degradation Mechanism: Fzo1 turnover depends on GTP hydrolysis, as non-functional fzo1 mutants (e.g., T221A, D320A) accumulate to higher levels even in the presence of Mdm30 .
These interactions highlight a complex regulatory network controlling fzo1 activity, where both assembly and disassembly processes are tightly regulated to ensure proper mitochondrial fusion.
Recombinant Protein Production
For experimental studies, recombinant fzo1 protein can be produced with various tags to facilitate purification and analysis. The most common approach involves:
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Expression System: E. coli-based expression of His-tagged fzo1 protein .
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Purification: Metal affinity chromatography using the His tag, yielding protein with greater than 90% purity .
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Storage Conditions: Lyophilized powder stored at -20°C to -80°C, with reconstitution in deionized sterile water to a concentration of 0.1-1.0 mg/mL, preferably with added glycerol (5-50%) .
These standardized approaches allow researchers to obtain high-quality recombinant fzo1 protein for in vitro studies of its biochemical properties and interactions.
Functional Assays
Several experimental approaches have been employed to study fzo1 function in mitochondrial fusion:
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Subcellular Localization: Fluorescence microscopy to visualize fzo1 localization to mitochondria .
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Complex Formation Analysis: Sucrose gradient centrifugation, crosslinking experiments, and blue native PAGE to study fzo1 dimerization and higher-order complex formation .
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Mutational Analysis: Site-directed mutagenesis of key residues in the GTPase domain to assess their roles in fzo1 function .
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Phenotypic Assays: Growth tests on glycerol medium to evaluate respiratory function in various fzo1 mutant strains .
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Overexpression Studies: Analysis of mitochondrial morphology upon overexpression of fzo1 from a heterologous promoter, which has been shown to induce mitochondrial aggregation .
These diverse experimental approaches have contributed to our current understanding of fzo1 structure, function, and regulation in mitochondrial dynamics.
Product Specs
Note: We prioritize shipping the format currently in stock. However, if you have specific format requirements, please indicate them during order placement, and we will accommodate your request.
Note: All proteins are shipped with standard blue ice packs by default. If dry ice shipping is required, please inform us in advance as additional fees will apply.
Generally, the shelf life of liquid form is 6 months at -20°C/-80°C. Lyophilized form has a shelf life of 12 months at -20°C/-80°C.
Target Background
KEGG: spo:SPBC1706.03
STRING: 4896.SPBC1706.03.1
Q&A
What is the primary function of fzo1 in Schizosaccharomyces pombe?
Fzo1 in S. pombe functions as a natural tether between mitochondria and peroxisomes (PerMit tether). Research demonstrates that Fzo1 naturally localizes to peroxisomes where it associates with mitochondrial Fzo1, creating contact sites between these organelles . Experimental evidence indicates that Fzo1 is involved in approximately 7-12% of all PerMit contacts in wild-type cells, confirming its role as a natural inter-organelle tether .
How does the GTPase domain influence fzo1 function?
The GTPase domain of Fzo1 is crucial for its membrane tethering capacity. Mutations in this domain, particularly the S201N mutation, inhibit oligomerization properties and prevent binding to Mdm30 (a regulator protein) . Experimental data shows that the GTPase mutant Fzo1 S201N becomes stabilized even in the presence of Mdm30, resulting in increased levels of extra-mitochondrial Fzo1 . This mutation decreases mitochondria-peroxisome contacts by approximately 7-12% compared to wild-type cells, demonstrating the importance of GTPase activity for proper tethering function .
How does fzo1 differ from other GTPases in S. pombe?
Unlike other GTPases in S. pombe such as Rho1p and Rho2p (which regulate cell wall integrity and morphogenesis), Fzo1 specifically mediates organelle contacts . While Rho GTPases interact with protein kinase C homologues to coordinate cell wall biosynthetic enzymes and actin organization , Fzo1 functions in the inter-organelle communication network. Additionally, unlike Mgm1 (another mitochondrial GTPase involved in inner membrane fusion), Fzo1 has the unique ability to localize to peroxisomes and facilitate PerMit contacts .
What is the relationship between fatty acid metabolism and fzo1-mediated contacts?
Research demonstrates a significant correlation between fatty acid desaturation levels and Fzo1-mediated organelle contacts. Higher expression of Ole1 (the fatty acid desaturase) leads to increased accumulation of Fzo1 on peroxisomes and enhances PerMit contacts by approximately 10% . Conversely, reduced Ole1 expression correlates with decreased PerMit contacts by about 10% . This evidence suggests that fatty acid metabolism plays a regulatory role in organelle communication through modulation of Fzo1 localization and function.
How can researchers distinguish between fzo1's roles in mitochondrial fusion versus organelle tethering?
To differentiate these functions, researchers should employ comparative analyses between fzo1 mutants and mutants of other fusion proteins. The research data shows that inactivation of MGM1 (the GTPase involved in inner membrane fusion) does not affect PerMit contacts, whereas mutations in Fzo1's GTPase domain decrease these contacts . This indicates that Fzo1's tethering function can be separated from general mitochondrial fusion processes. Experimental designs should include appropriate controls and specialized mutants that affect specific aspects of Fzo1 function.
What experimental evidence supports the localization of fzo1 to peroxisomes?
Multiple experimental approaches confirm Fzo1's peroxisomal localization:
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Cell fractionation studies show Fzo1 presence in cytosolic supernatants devoid of mitochondria
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Immunoprecipitation of native peroxisomes from cytosolic fractions directly demonstrates Fzo1 association with peroxisomes
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Quantitative analysis reveals that mutations in the GTPase domain (S201N) increase peroxisomal Fzo1 levels by more than 80%
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Microscopy with fluorescently tagged proteins (Pex3-mCherry and GFP-Fzo1) visualizes Fzo1 at mitochondria-peroxisome contact sites
What techniques are most effective for studying fzo1-mediated organelle contacts?
Based on current research practices, the most robust approach combines multiple methodologies:
| Technique | Application | Advantage |
|---|---|---|
| Cell fractionation | Isolation of mitochondrial and cytosolic fractions | Allows biochemical characterization of Fzo1 distribution |
| Immunoprecipitation | Isolation of Fzo1-associated complexes | Identifies interaction partners and quantifies relative abundance |
| Fluorescence microscopy | Visualization of PerMit contacts | Enables direct observation and quantification of contacts in vivo |
| Genetic manipulation | Creation of specific mutants | Enables functional analysis of protein domains |
| Promoter modulation | Control of gene expression levels | Allows correlation between protein levels and phenotypic outcomes |
Researchers should implement these techniques in combination to comprehensively characterize Fzo1 function in organelle contacts .
What experimental controls are essential when studying fzo1 mutants?
Critical controls include:
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Wild-type Fzo1 expression for baseline comparison
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Mutations in other mitochondrial GTPases (e.g., Mgm1) to distinguish Fzo1-specific effects
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Total protein level measurements to ensure expression level changes aren't responsible for observed phenotypes
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Empty vector controls for overexpression studies
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Verification of organelle marker specificity for localization studies
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Inclusion of multiple independently derived mutant strains to eliminate clone-specific effects
How do mutations in the GTPase domain quantitatively affect fzo1 function?
The S201N mutation in Fzo1's GTPase domain produces several quantifiable effects:
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Increases peroxisomal Fzo1 levels by >80% compared to wild-type
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Affects the oligomerization properties of Fzo1, preventing proper tethering function
These data demonstrate that GTPase activity is essential for normal Fzo1 distribution and function in organelle tethering.
What is the relationship between fzo1 and other mitochondrial proteins?
While Fzo1 functions in organelle tethering, it operates within a network of other mitochondrial proteins. Unlike Mgm1, which specifically regulates inner membrane fusion without affecting PerMit contacts, Fzo1 has dual roles . Research should consider potential interactions between Fzo1 and other proteins involved in mitochondrial dynamics and function. The relationship between Fzo1 and Mls1 (mentioned in the research but not fully characterized) suggests additional functional connections that warrant further investigation .
How can researchers manipulate fzo1 activity to study its physiological roles?
Several experimental approaches can modulate Fzo1 activity:
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Introduction of specific mutations (e.g., S201N) to disrupt GTPase function
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Modulation of Ole1 expression to indirectly influence Fzo1 localization and function
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Manipulation of Mdm30 levels to affect Fzo1 stability and turnover
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Use of inducible promoters to control temporal expression
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Generation of chimeric proteins to alter subcellular targeting
Each approach offers distinct advantages for investigating specific aspects of Fzo1 biology.
How does research on S. pombe fzo1 relate to mitochondrial diseases?
S. pombe Fzo1 research provides a model for understanding fundamental processes relevant to mitochondrial diseases. The inter-organelle communication mediated by Fzo1 potentially influences mitochondrial metabolism, quality control, and homeostasis. Since human mitofusins (homologs of Fzo1) are implicated in Charcot-Marie-Tooth neuropathy type 2A and other disorders, mechanistic insights from S. pombe can inform therapeutic approaches. The connection between fatty acid metabolism and organelle contacts revealed in S. pombe may represent a conserved regulatory mechanism relevant to human disease .
What advantages does S. pombe offer as a model for studying fzo1 compared to other organisms?
S. pombe provides several experimental advantages:
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Genetic tractability with well-established tools for gene manipulation
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Cellular organization more similar to metazoans than S. cerevisiae in some aspects
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Simpler system for studying organelle interactions than mammalian cells
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Ability to easily create and phenotype mutants
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Availability of genome-wide deletion and overexpression libraries
These advantages make S. pombe an excellent model for dissecting the molecular mechanisms of Fzo1 function and regulation.
What are emerging research directions for fzo1 studies?
Current research suggests several promising directions:
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Exploring the relationship between fatty acid metabolism, membrane composition, and organelle contacts
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Investigating the molecular mechanisms by which Fzo1 facilitates tethering
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Examining the physiological significance of modulating PerMit contacts under different cellular conditions
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Identifying additional regulatory factors that influence Fzo1 localization and function
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Comparing the mechanisms of Fzo1-mediated tethering across evolutionary diverse organisms
These emerging areas promise to expand our understanding of organelle communication networks and their importance in cellular physiology.
