Recombinant Protein SEY1 homolog 1 (GSPATT00029660001)

How is SEY1 homolog 1 related to other dynamin-like GTPases?

SEY1 homolog 1 belongs to a family of dynamin-like GTPases that includes the atlastins (ATLs) in mammals and RHD3 in plants . These proteins share functional similarities despite limited sequence homology. Studies have shown that in Saccharomyces cerevisiae, Sey1p (the yeast homolog) can be partially replaced by mammalian ATL1, suggesting functional conservation across species .

Interestingly, no organism appears to possess both ATL and Sey1p homologues, indicating potential functional redundancy . The structural organization of these proteins is similar, with all containing a GTPase domain, a helical bundle domain (longer in Sey1p than in ATLs), transmembrane segments, and a C-terminal tail . Functionally, both Sey1p and ATLs mediate ER membrane fusion through GTP-dependent mechanisms and undergo GTP-dependent dimerization .

What expression systems are available for producing Recombinant SEY1 homolog 1?

Several expression systems are available for the production of Recombinant SEY1 homolog 1, each with specific advantages depending on the research application:

The choice of expression system should be based on the specific requirements of the research question, including the need for post-translational modifications, protein folding considerations, and the intended experimental applications .

What are the optimal storage conditions for Recombinant SEY1 homolog 1?

For optimal stability and activity retention, Recombinant SEY1 homolog 1 should be stored according to the following guidelines:

Upon receipt, the lyophilized protein should be briefly centrifuged to bring the contents to the bottom of the vial . For long-term storage, the protein should be stored at -20°C or preferably -80°C . When reconstituting the protein, it is recommended to use deionized sterile water to a concentration of 0.1-1.0 mg/mL .

To prevent protein degradation during freeze-thaw cycles, it is advisable to add glycerol to a final concentration of 5-50% (with 50% being the standard recommendation) and aliquot the protein solution before freezing . For working aliquots that will be used within one week, storage at 4°C is acceptable, but repeated freezing and thawing should be avoided . The protein is typically supplied in a Tris/PBS-based buffer containing 6% trehalose at pH 8.0, which helps maintain stability during storage .

How can I design experiments to study the GTPase activity of SEY1 homolog 1?

To effectively investigate the GTPase activity of SEY1 homolog 1, researchers should consider a multi-faceted experimental approach:

First, establish a purified protein system using the His-tagged recombinant protein expressed in E. coli or another suitable system . The purified protein should be of high quality (>90% purity as determined by SDS-PAGE) . For GTPase activity assays, consider using either colorimetric phosphate release assays, HPLC-based nucleotide conversion assays, or coupled enzymatic assays that link GTP hydrolysis to NADH oxidation.

A key control would be the K50A mutant of Sey1p, which has been shown to have significantly reduced GTPase activity . This mutation in the P-loop of the GTPase domain serves as an excellent negative control in activity assays. The study by Hu et al. demonstrated that even the residual GTPase activity of Sey1p-K50A was insufficient to support normal ER fusion in vitro .

For kinetic analysis, measure GTPase activity at various substrate concentrations to determine Km and kcat values. Additionally, investigate the effect of dimerization on GTPase activity by comparing the protein's activity in monomeric versus dimeric states, which can be modulated by the presence of different nucleotides (GDP vs. GDP-AlFx) .

What experimental approaches can be used to study SEY1 homolog 1 dimerization?

SEY1 homolog 1 undergoes GTP-dependent dimerization, which is crucial for its function in ER membrane fusion . Several approaches can be employed to study this process:

Sedimentation velocity analysis has been successfully used to demonstrate that Sey1p transitions from a monomeric to dimeric state in a nucleotide-dependent manner . This technique showed that Sey1p-ΔTM (with transmembrane domains replaced by a 12-amino acid linker) runs primarily as a monomer in the absence of nucleotide or in the presence of GDP, but forms dimers in the presence of GDP and AlFx, which mimics the transition state of nucleotide hydrolysis .

Other valuable techniques include:

• Size exclusion chromatography coupled with multi-angle light scattering (SEC-MALS) to determine the absolute molecular mass of protein complexes in solution

• Fluorescence resonance energy transfer (FRET) using differentially labeled SEY1 homolog 1 proteins to monitor dimerization in real-time

• Cross-linking studies followed by mass spectrometry to identify interaction interfaces

• Analytical ultracentrifugation to determine the sedimentation coefficient and molecular weight of protein complexes

When designing these experiments, it's important to consider the role of the transmembrane domains. While the Sey1p-ΔTM construct allows for soluble protein studies, the transmembrane domains may contribute to the stability or orientation of the dimers in the native context .

How can I set up an in vitro fusion assay using purified SEY1 homolog 1?

Establishing an in vitro fusion assay using purified SEY1 homolog 1 requires several carefully designed components:

First, purify SEY1 homolog 1 to high homogeneity (>90% purity) . Then prepare proteoliposomes by reconstituting the purified protein into liposomes composed of physiologically relevant lipids. The protein-to-lipid ratio should be optimized to ensure efficient incorporation while maintaining protein function.

For monitoring fusion, several approaches can be used:

• Lipid mixing assays using fluorescently labeled lipids (such as NBD-PE and Rh-PE) incorporated into one population of proteoliposomes

• Content mixing assays using encapsulated fluorescent molecules

• FRET-based assays to monitor membrane proximity and fusion

Based on the studies with Sey1p, the fusion reaction should be conducted in the presence of GTP, as fusion is GTP-dependent . A crucial control is the K50A mutant, which has significantly reduced GTPase activity and does not support efficient fusion . Additional controls should include reactions without nucleotide or with non-hydrolyzable GTP analogs.

The research by Hu et al. demonstrated that no fusion occurs between proteoliposomes containing Sey1p and liposomes without Sey1p, indicating that the protein must be present in both membranes for fusion to occur . This critical finding should be verified in your system by testing fusion between proteoliposomes containing SEY1 homolog 1 and protein-free liposomes.

What methods can be used to investigate SEY1 homolog 1's role in ER membrane dynamics?

To investigate SEY1 homolog 1's role in ER membrane dynamics, researchers can employ several complementary approaches:

For in vivo studies, fluorescent protein tagging and live-cell imaging provide valuable insights. An elegant approach developed for studying ER fusion involves mating haploid yeast cells expressing different fluorescent markers (cytosolic GFP in one cell and ER-luminal RFP in another) and monitoring the redistribution of these markers after cell fusion . This technique revealed that in wild-type cells, ER content equilibrates within approximately 4 minutes after cell fusion, while in sey1Δ cells, this process takes about 25 minutes .

For biochemical analyses, co-immunoprecipitation can identify interaction partners. SEY1 homolog 1 has been shown to interact with tubule-shaping proteins like Rtn1p and Yop1p (homologues of reticulons and DP1) . Quantitative proteomics approaches can further elucidate the protein interaction network.

Advanced imaging techniques such as super-resolution microscopy or electron microscopy can provide detailed visualization of ER morphology changes associated with SEY1 homolog 1 function or dysfunction.

What considerations are important when designing mutations to study SEY1 homolog 1 function?

When designing mutations to study SEY1 homolog 1 function, several key considerations should guide your approach:

First, focus on conserved functional domains. The protein contains a dynamin-like GTPase domain with characteristic signature motifs, a helical bundle domain, transmembrane segments, and a C-terminal tail . The K50A mutation in the P-loop of the GTPase domain has been well-characterized and significantly reduces GTPase activity, making it an excellent choice for studying the importance of GTP hydrolysis .

Consider the dimeric interface, as dimerization is critical for function. The research showed that Sey1p undergoes GTP-dependent dimerization, transitioning from monomer to dimer in the presence of GDP-AlFx . Mutations at the dimer interface could provide insights into the mechanism of dimerization and its role in ER fusion.

The transmembrane domains are essential for proper membrane anchoring and orientation. While removing these domains (as in the Sey1p-ΔTM construct) allows for soluble protein studies, it eliminates the protein's ability to mediate membrane fusion . Mutations that alter the length or hydrophobicity of these domains could reveal how membrane insertion contributes to function.

When expressing mutant proteins, ensure they are properly localized to the ER. Immunofluorescence or fluorescent protein tagging can confirm correct localization. Additionally, verify that mutations do not simply destabilize the protein by checking expression levels and stability.

Finally, consider the redundancy with SNARE-mediated fusion. Research has shown that in the absence of Sey1p, ER fusion can still occur through a mechanism involving the ER SNARE Ufe1p . This suggests that comprehensive functional studies should address both pathways.

How does the function of SEY1 homolog 1 compare across different species?

SEY1 homolog proteins exhibit functional conservation across diverse eukaryotic species despite limited sequence homology. In Saccharomyces cerevisiae, Sey1p mediates homotypic ER fusion through a GTP-dependent mechanism similar to that of mammalian atlastins . Experiments have demonstrated that human ATL1 can partially replace Sey1p function when expressed in yeast, confirming functional conservation .

In contrast to yeast, mammals utilize atlastins rather than Sey1 homologs for ER fusion. These proteins share structural features including a GTPase domain, helical bundles, and transmembrane segments, though the helical bundle in Sey1p is significantly longer than that in atlastins . Plants employ RHD3, another SEY1-related protein, for ER morphology maintenance .

Interestingly, no organism appears to possess both ATL and Sey1p homologues, suggesting they evolved as alternative solutions to the same biological problem . This evolutionary pattern implies functional equivalence despite structural differences.

A key distinction between species is the presence of redundant fusion mechanisms. In yeast, cells lacking Sey1p show delayed but not abolished ER fusion, indicating an alternative pathway involving ER SNAREs, particularly Ufe1p . This redundancy may vary across species, affecting the phenotypic consequences of SEY1 homolog dysfunction.

What are common challenges in working with Recombinant SEY1 homolog 1 and how can they be addressed?

Researchers working with Recombinant SEY1 homolog 1 frequently encounter several challenges that can be addressed through specific methodological approaches:

Maintaining GTPase activity during purification can be difficult. To preserve activity, include GTP or GDP in purification buffers, minimize exposure to high temperatures, and use freshly prepared proteins for assays. The storage recommendations include adding 5-50% glycerol and storing at -20°C/-80°C in small aliquots to avoid freeze-thaw cycles .

For functional assays, the orientation of the protein in reconstituted liposomes is critical. Random orientation during reconstitution can reduce the observable activity. Techniques such as protease protection assays can be used to determine protein orientation in liposomes, and optimizing reconstitution protocols can improve the percentage of correctly oriented protein.

When investigating protein-protein interactions, weak or transient interactions may be difficult to detect. Approaches such as chemical cross-linking prior to immunoprecipitation, proximity labeling techniques, or the use of transition state mimics like GDP-AlFx can stabilize interaction complexes for detection .

How can I validate antibodies for detecting endogenous SEY1 homolog 1 in different experimental systems?

Validating antibodies for detecting endogenous SEY1 homolog 1 requires a systematic approach to ensure specificity and sensitivity:

Begin with knockout or knockdown controls. Generate cells lacking SEY1 homolog 1 expression (sey1Δ in yeast or CRISPR-mediated knockout in other systems) to serve as negative controls . A specific antibody should show significantly reduced or absent signal in these samples compared to wild-type.

Overexpression validation complements knockout controls. Express tagged versions of SEY1 homolog 1 and confirm that the antibody detects both endogenous and overexpressed protein with correct molecular weight differences accounting for the tag.

Cross-reactivity testing is essential, especially in systems expressing similar proteins. Test the antibody against related proteins like atlastins or other dynamin-like GTPases to ensure specificity. This is particularly important when working with new model systems.

For immunofluorescence applications, perform co-localization studies with established ER markers. SEY1 homolog 1 should primarily localize to the tubular ER network . Additionally, competitor peptide blocking can confirm specificity - pre-incubation of the antibody with the immunizing peptide should abolish specific staining.

Multiple detection methods provide robust validation. Compare results from Western blotting, immunoprecipitation, and immunofluorescence to ensure consistent detection across techniques. Different lots of antibodies should also be compared to account for batch variation.