Recombinant Vitis vinifera CASP-like protein VIT_14s0068g01400 (VIT_14s0068g01400)

What is VIT_14s0068g01400 and what is its function in Vitis vinifera?

VIT_14s0068g01400 (also known as VvCASPL1F2) is a CASP-like protein from Vitis vinifera (grape). It belongs to the family of Casparian Strip Membrane Domain Proteins (CASPs), which are four-membrane-span proteins that mediate the deposition of Casparian strips in plant endodermal cells by recruiting lignin polymerization machinery . While the specific function of VIT_14s0068g01400 in Vitis vinifera has not been fully characterized, CASP proteins generally play crucial roles in plant responses to environmental stresses and are involved in the formation of membrane domains that direct local cell wall modifications . This protein shows high stability in its membrane domain, presenting hallmarks of a membrane scaffold that could be involved in establishing specialized plasma membrane domains.

How does VIT_14s0068g01400 relate to other CASP-like proteins in the plant kingdom?

VIT_14s0068g01400 is part of the broader CASP-like (CASPL) protein family that has been found in all major divisions of land plants and green algae . Based on phylogenetic analyses, CASP proteins have been categorized into different subfamilies, with varying distributions across plant species. Interestingly, CASPL proteins show conservation with the MARVEL protein family found outside the plant kingdom, with conserved residues primarily located in the transmembrane domains . This conservation pattern suggests that the membrane-scaffolding function of these proteins is evolutionarily ancient. The specific subfamily classification of VIT_14s0068g01400 within the CASPL family would provide insights into its potential functional relationships with other CASPs involved in processes such as Casparian strip formation or other specialized membrane domain formations in plants.

What expression systems are available for producing recombinant VIT_14s0068g01400?

Recombinant VIT_14s0068g01400 can be expressed in multiple heterologous systems, each offering distinct advantages for different experimental purposes:

• E. coli expression system: The most commonly used system, providing high yield and cost-effectiveness. The protein is typically expressed with an N-terminal His-tag for purification purposes .

• Yeast expression system: Offers post-translational modifications more similar to those in plants compared to bacterial systems, potentially yielding protein with more native-like properties .

• Baculovirus expression system: Provides higher eukaryotic post-translational modifications and is useful for proteins that require complex folding or processing .

• Mammalian cell expression system: Offers the most sophisticated post-translational modifications, though at higher cost and typically lower yield .

• In vivo biotinylation: Some suppliers offer the protein with an Avi-tag that is biotinylated in vivo using E. coli biotin ligase (BirA) technology, which can be advantageous for protein-protein interaction studies, immunoprecipitation, or pull-down assays .

The choice of expression system should be based on the specific research needs, including required protein folding, post-translational modifications, yield requirements, and downstream applications.

What is the optimal storage and handling procedure for recombinant VIT_14s0068g01400?

For optimal stability and activity of recombinant VIT_14s0068g01400:

• Storage temperature: Store at -20°C for short-term storage or -80°C for extended storage periods .

• Storage buffer: The protein is typically provided in a Tris-based buffer containing 50% glycerol or Tris/PBS-based buffer with 6% trehalose at pH 8.0 .

• Reconstitution: If provided as a lyophilized powder, it should be briefly centrifuged prior to opening. Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL .

• Aliquoting: To prevent repeated freeze-thaw cycles, divide the reconstituted protein into small working aliquots. Working aliquots can be stored at 4°C for up to one week .

• Glycerol addition: For long-term storage, adding glycerol to a final concentration of 50% is recommended before freezing aliquots .

Repeated freeze-thaw cycles should be avoided as they can lead to protein denaturation and loss of activity, potentially compromising experimental results.

What experimental validation methods are appropriate for confirming VIT_14s0068g01400 identity and activity?

To validate the identity and assess the activity of recombinant VIT_14s0068g01400:

• SDS-PAGE: Confirm protein size and purity. Expected molecular weight would be approximately 21 kDa plus any tag mass. Purity should be greater than 85-90% .

• Western blotting: Use anti-His antibodies for His-tagged protein or specific antibodies against VIT_14s0068g01400, if available.

• Mass spectrometry: For definitive identification and to verify the intact mass or peptide fingerprint.

• Circular dichroism (CD): To assess secondary structure and proper folding.

• Membrane localization assays: Since CASPs form membrane domains, fluorescently tagged VIT_14s0068g01400 can be expressed in model plant systems to observe its localization pattern and domain-forming capability .

• Complementation assays: Test the protein's ability to rescue phenotypes in CASP mutant plants or heterologous systems.

• Protein-protein interaction studies: Investigate interactions with other membrane or cell wall-related proteins using techniques such as co-immunoprecipitation, yeast two-hybrid, or bimolecular fluorescence complementation.

Given the membrane scaffolding role of CASP proteins, functional validation should focus on its ability to localize correctly and form stable membrane domains rather than enzymatic activity per se.

How can VIT_14s0068g01400 be utilized to study membrane domain formation in plants?

VIT_14s0068g01400 provides an excellent model for studying specialized membrane domain formation in plants through several advanced approaches:

• Domain formation assessment: Express fluorescently-tagged VIT_14s0068g01400 in heterologous plant systems to observe its membrane localization patterns. CASP proteins show high stability in their membrane domains, exhibiting restricted lateral diffusion characteristic of membrane scaffolds . This can be quantified using fluorescence recovery after photobleaching (FRAP) techniques.

• Mutagenesis studies: Systematic modification of transmembrane domains and conserved residues can reveal critical regions for membrane domain formation. The conservation between CASPLs and MARVEL proteins suggests that transmembrane domains are particularly important, with extracellular loops potentially being dispensable for scaffold formation .

• Heterologous expression in endodermis: Like other CASPLs, VIT_14s0068g01400 might integrate into the CASP membrane domain when ectopically expressed in the endodermis, providing insights into the requirements for membrane scaffold incorporation .

• Super-resolution microscopy: Techniques such as STORM or PALM can visualize the nanoscale organization of VIT_14s0068g01400 in membrane domains and how it interacts with other membrane components.

• Lipidomic analysis of VIT_14s0068g01400-containing membrane domains: This can reveal specific lipid compositions that facilitate domain formation and stability.

These approaches can reveal fundamental mechanisms of membrane compartmentalization in plants and how specialized membrane domains facilitate localized cell wall modifications.

What comparative analyses can be performed between VIT_14s0068g01400 and other CASP family proteins?

Several sophisticated comparative analyses can provide insights into VIT_14s0068g01400's evolutionary and functional relationships:

• Phylogenetic analysis: Position VIT_14s0068g01400 within the broader CASP/CASPL family tree to identify its closest relatives and subfamily classification. This can reveal potential functional specializations based on evolutionary relationships .

• Comparative expression profiling: Analyze tissue-specific and stress-responsive expression patterns compared to other CASP family members, which may indicate functional divergence or conservation.

• Domain architecture comparison: Analyze conservation patterns in transmembrane domains versus loop regions across CASPs, CASPLs, and MARVEL proteins. Focus particularly on conserved basic (Arg, His, Lys) and acidic (Asp, Glu) amino acids in TM1 and TM3, which show significant conservation in this protein family .

• Synteny analysis: Examine genomic collinearity between VIT_14s0068g01400 and other CASP genes to understand evolutionary history. Such analysis has already revealed collinear CASP homologous gene pairs between rice and Arabidopsis, suggesting conserved genomic arrangements across species .

• Functional complementation experiments: Test the ability of VIT_14s0068g01400 to rescue phenotypes of CASP mutants from Arabidopsis or other model plants to assess functional conservation.

This multi-faceted comparative approach can reveal the extent of functional conservation versus specialization of VIT_14s0068g01400 within the broader context of plant membrane domain proteins.

What role might VIT_14s0068g01400 play in grapevine stress responses and how can this be investigated?

Investigation of VIT_14s0068g01400's potential role in grapevine stress responses can be approached through several advanced experimental designs:

• Stress-responsive expression analysis: Quantify expression levels of VIT_14s0068g01400 under various abiotic stresses (drought, salinity, temperature extremes) and biotic stresses (pathogen infection) using qRT-PCR or RNA-seq approaches.

• CRISPR/Cas9-mediated knockout or RNAi-mediated knockdown: Generate grapevine lines with reduced or eliminated VIT_14s0068g01400 expression to assess phenotypic consequences under normal and stress conditions.

• Overexpression studies: Create transgenic grapevine lines overexpressing VIT_14s0068g01400 to assess whether enhanced expression confers improved stress tolerance.

• Subcellular localization changes: Monitor potential stress-induced relocalization using fluorescently tagged protein, as membrane domain reorganization may occur during stress responses.

• Interaction proteomics: Identify stress-dependent protein interaction partners using techniques such as co-immunoprecipitation followed by mass spectrometry under normal versus stress conditions.

• Physiological parameter assessment: Measure parameters like ion leakage, water potential, photosynthetic efficiency, and reactive oxygen species accumulation in modified versus control plants under stress conditions.

Since CASP proteins are involved in forming Casparian strips that control selective nutrient uptake, VIT_14s0068g01400 may particularly influence mineral nutrition efficiency and water transport during stress, making these parameters especially relevant to assess.

What are common challenges in expressing and purifying functional VIT_14s0068g01400 and how can they be addressed?

Working with membrane proteins like VIT_14s0068g01400 presents several challenges that can be overcome with appropriate strategies:

• Low expression yield:

  • Problem: Membrane proteins often express poorly in heterologous systems.

  • Solution: Optimize codon usage for the expression host; use stronger promoters; test different expression conditions (temperature, induction time); try fusion tags known to enhance solubility (MBP, SUMO); consider specialized E. coli strains designed for membrane protein expression.

• Protein aggregation:

  • Problem: Hydrophobic transmembrane domains can cause aggregation.

  • Solution: Express at lower temperatures (16-20°C); add mild detergents during lysis; include stabilizing agents like glycerol or trehalose in buffers ; consider expressing only soluble domains if full-length protein proves refractory.

• Improper folding:

  • Problem: Incorrect disulfide bond formation or tertiary structure.

  • Solution: Express in eukaryotic systems (yeast, insect, or mammalian cells) that provide appropriate folding machinery ; include redox buffer components during purification.

• Instability after purification:

  • Problem: Loss of structure/function during storage.

  • Solution: Optimize buffer conditions (pH, salt concentration); add stabilizing agents; store with glycerol at -80°C in small aliquots ; avoid repeated freeze-thaw cycles.

• Tag interference with function:

  • Problem: Affinity tags may affect protein function or interaction studies.

  • Solution: Include a cleavable linker between the protein and tag; test both N- and C-terminal tag positions; consider tag-free purification protocols if necessary.

• Low purity:

  • Problem: Co-purifying contaminants.

  • Solution: Implement multi-step purification strategy; optimize imidazole concentrations for His-tagged proteins; consider size exclusion chromatography as a final polishing step.

These strategies should be systematically tested to determine the optimal conditions for obtaining functional VIT_14s0068g01400 suitable for downstream applications.

How can researchers determine if recombinant VIT_14s0068g01400 retains native conformation and functionality?

Assessing whether recombinant VIT_14s0068g01400 maintains its native structure and function requires multiple complementary approaches:

• Biophysical characterization:

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

  • Thermal shift assays to evaluate protein stability

  • Size exclusion chromatography to verify monodispersity and appropriate oligomeric state

  • Limited proteolysis to probe for well-folded domains resistant to digestion

• Functional assays:

  • Membrane integration assessment: Reconstitution into liposomes or nanodiscs followed by flotation assays

  • Lateral mobility measurements: FRAP analysis of fluorescently tagged protein in membrane environments

  • Domain formation capacity: Co-localization with known CASP domain markers when expressed in plant cells

• Comparative analysis:

  • Side-by-side comparison of key properties between recombinant protein from different expression systems (bacterial vs. yeast vs. insect cell)

  • Comparison with native protein extracted from Vitis vinifera tissue (if feasible)

• Complementation testing:

  • Ability to rescue phenotypes in CASP-family mutant plants

  • Capacity to form appropriate membrane domains when expressed in heterologous systems

• Interaction verification:

  • Binding studies with known CASP-interacting proteins

  • Recruitment of lignin polymerization machinery components, which is a known function of CASP proteins

When possible, comparing results across multiple expression systems can provide confidence that the observed properties reflect intrinsic characteristics of VIT_14s0068g01400 rather than artifacts of a particular recombinant production method.

How does VIT_14s0068g01400 relate to CASP proteins in other species in terms of structure and function?

VIT_14s0068g01400 from Vitis vinifera can be contextualized within the broader evolutionary framework of CASP proteins through comparative analysis:

• Structural conservation: VIT_14s0068g01400 shares the characteristic four-transmembrane domain architecture of CASP proteins, with particular conservation in the transmembrane regions rather than the loop regions . This pattern of conservation is consistent with the proposed role of transmembrane domains in scaffold formation and membrane domain establishment.

• Phylogenetic positioning: CASP and CASP-like proteins form distinct subfamilies across plant species. Detailed phylogenetic analysis would place VIT_14s0068g01400 within these subfamilies, providing insights into its potential functional specialization. The protein's UniProt annotation as "CASP-like protein 1F2" (VvCASPL1F2) suggests specific subfamily classification .

• Functional inference: The closest well-characterized relatives of VIT_14s0068g01400 in model plants like Arabidopsis could provide functional insights. For instance, AtCASP1, AtCASP3, and OsCASP1 are known to be involved in endodermal Casparian strip formation and selective mineral uptake . Based on evolutionary relatedness, VIT_14s0068g01400 may share similar functions or have evolved specialized roles in grapevine.

• Domain comparisons with MARVEL proteins: The similarity between plant CASPLs and animal/fungal MARVEL proteins suggests an ancient evolutionary origin of this membrane-scaffolding module . Comparing conserved residues in VIT_14s0068g01400 with those in MARVEL proteins could reveal fundamental structural elements required for membrane domain formation across diverse eukaryotes.

• Species-specific adaptations: Unique structural features of VIT_14s0068g01400 compared to CASPs from other plants may reflect adaptations to grapevine-specific physiological or developmental processes.

This comparative evolutionary framework provides context for understanding both the conserved and specialized aspects of VIT_14s0068g01400's function in Vitis vinifera.

What insights can be gained from studying the genomic context of VIT_14s0068g01400?

Analysis of the genomic context of VIT_14s0068g01400 can provide valuable insights into its regulation, evolution, and functional relationships:

• Promoter analysis: Examination of the upstream regulatory region can reveal:

  • Cis-regulatory elements associated with developmental or stress-responsive expression

  • Conservation of regulatory elements with orthologous genes in other species

  • Potential co-regulation with functionally related genes

• Chromosomal localization: The position on chromosome 14 of Vitis vinifera genome (indicated by the "14s" prefix in the gene ID) may reveal:

  • Proximity to other CASP family members, suggesting tandem duplication events

  • Co-localization with genes involved in related processes (e.g., cell wall modification, transport)

  • Syntenic relationships with chromosomal regions in other plant species

• Gene structure analysis: Examination of exon-intron organization can provide:

  • Insights into evolutionary history through comparison with orthologs

  • Evidence of alternative splicing potential

  • Information about protein domain modularity

• Genomic collinearity: Analysis of syntenic relationships can identify:

  • Orthologous relationships with CASP genes in model plants

  • Evidence of whole-genome duplication events in the history of this gene family

  • Cases of gene retention versus gene loss following duplication events

• Transposable element associations: Proximity to or evidence of historic transposable element activity could suggest:

  • Mechanisms for gene duplication or regulatory innovation

  • Potential for stress-responsive regulation, as many TEs are activated under stress

Comprehensive genomic context analysis would complement protein-level studies and provide a more complete understanding of VIT_14s0068g01400's biological role and evolutionary history in grapevine.

What experimental approaches can determine if VIT_14s0068g01400 is involved in Casparian strip formation in grapevine roots?

Determining whether VIT_14s0068g01400 participates in Casparian strip formation in grapevine roots requires a multi-faceted experimental approach:

• Expression pattern analysis:

  • Tissue-specific expression: Quantify expression levels in different root zones using qRT-PCR, particularly in the endodermis where Casparian strips form.

  • Developmental timing: Analyze expression during root development stages coinciding with Casparian strip formation.

  • Cellular localization: Perform in situ hybridization or use promoter:reporter constructs to visualize expression patterns at cellular resolution.

• Subcellular localization studies:

  • Express fluorescently tagged VIT_14s0068g01400 in grapevine roots.

  • Assess co-localization with established Casparian strip markers.

  • Examine localization pattern for the characteristic "band-like" arrangement around endodermal cells typical of CASP proteins in Arabidopsis .

• Functional perturbation:

  • Generate CRISPR/Cas9 knockout or RNAi knockdown grapevine lines.

  • Assess Casparian strip integrity using apoplastic tracer dyes (e.g., propidium iodide).

  • Evaluate functional consequences through measurements of ion uptake selectivity and water transport.

• Protein interaction studies:

  • Identify interaction partners through co-immunoprecipitation or proximity labeling techniques.

  • Test for interactions with known Casparian strip formation components (e.g., peroxidases, ESB1).

  • Perform bimolecular fluorescence complementation (BiFC) to verify interactions in planta.

• Complementation analysis:

  • Express VIT_14s0068g01400 in Arabidopsis casp mutants to test for functional conservation.

  • Assess restoration of Casparian strip integrity and function.

• Ultrastructural analysis:

  • Perform transmission electron microscopy of wild-type and VIT_14s0068g01400-modified roots.

  • Look for alterations in Casparian strip formation, deposition, or maturation.

Integration of these multiple lines of evidence would provide compelling support for or against the involvement of VIT_14s0068g01400 in Casparian strip formation in grapevine roots.