Recombinant Vitis vinifera CASP-like protein VIT_01s0010g01870 (VIT_01s0010g01870)

What is CASP-like protein VIT_01s0010g01870 and how is it classified?

CASP-like protein VIT_01s0010g01870 (officially named CASP-like protein 2A1, NCBI GeneID: 100249479) is a four-transmembrane protein from Vitis vinifera that belongs to the broader family of CASP-like (CASPL) proteins. This protein has a molecular weight of 21,968 Da and shares structural similarities with CASPARIAN STRIP MEMBRANE DOMAIN PROTEINS (CASPs), which are involved in forming membrane scaffolds and directing cell wall modifications .

From an evolutionary perspective, CASPLs are found across all major divisions of land plants and green algae, with VIT_01s0010g01870 representing a specific variant in grapevine. Interestingly, CASPL proteins show homology to the MARVEL protein family found outside the plant kingdom, indicating a deep evolutionary conservation of this protein structure .

What experimental techniques are optimal for purifying recombinant VIT_01s0010g01870?

For optimal purification of recombinant VIT_01s0010g01870, a multi-step approach is recommended:

• Expression System Selection: The protein can be expressed in E. coli, yeast, baculovirus, or mammalian cell systems. The choice depends on research requirements:

  • E. coli systems offer high yield but may have limitations for post-translational modifications

  • Mammalian and insect cell systems provide better folding for membrane proteins

• Purification Protocol:

  • Initial extraction using membrane solubilization buffers containing mild detergents

  • Affinity chromatography (if tagged) followed by size exclusion chromatography

  • Ion exchange chromatography for higher purity

• Quality Control:

  • SDS-PAGE analysis to confirm purity (target ≥85%)

  • Mass spectrometry to verify intact mass (expected 21,968 Da)

  • Western blot using anti-tag or specific antibodies

The purified protein should be stored at -20°C or -80°C for long-term storage, with working aliquots maintained at 4°C for up to one week to avoid repeated freeze-thaw cycles that could compromise structural integrity .

How can domain-specific mutagenesis be used to investigate VIT_01s0010g01870 function?

Domain-specific mutagenesis represents a powerful approach to dissect the functional significance of specific regions within VIT_01s0010g01870. Based on the conservation patterns observed in CASP/CASPL proteins, several targeted approaches can be employed:

Transmembrane Domain Mutagenesis:

• Target the highly conserved Asp residue in TM3 (equivalent to D134 in AtCASP1), which appears essential for proper protein folding

• Studies with related proteins show that mutations in this position can completely abolish protein expression or localization

Extracellular Loop Modifications:

• EL1 (first extracellular loop) shows poor conservation among CASPLs generally but contains a nine-amino acid signature (ESLPFFTQF) in spermatophytes that may have endodermis-specific functions

• EL2 (second extracellular loop) shows higher conservation and may be involved in protein-protein interactions

Experimental Design Table for Mutagenesis Studies:

When implementing this approach, researchers should incorporate fluorescent protein tags to monitor localization and use complementation assays in Arabidopsis mutants to assess functional rescue. The data from such studies would clarify which domains are essential for the protein's subcellular localization versus its functional interactions .

What techniques can resolve controversies about membrane domain formation by VIT_01s0010g01870?

Resolving controversies about membrane domain formation by VIT_01s0010g01870 requires multi-faceted approaches that examine both the protein's behavior and its interactions with membrane components:

• Advanced Imaging Techniques:

  • Super-resolution microscopy (STORM/PALM) to visualize nanoscale membrane domain formation

  • FRET analysis to measure protein-protein interactions within putative domains

  • Fluorescence recovery after photobleaching (FRAP) to assess membrane domain stability and protein turnover

• Biochemical Approaches:

  • Detergent-resistant membrane fractionation to isolate potential membrane domains

  • Co-immunoprecipitation with domain markers to identify interaction partners

  • Crosslinking mass spectrometry to capture transient interactions

• Heterologous Expression Systems:

  • Expression in the Arabidopsis endodermis to compare with known CASP behaviors

  • Yeast membrane systems to assess autonomous domain formation capacity

When interpreting results, researchers should specifically address whether VIT_01s0010g01870 forms stable membrane domains similar to those observed with CASPs in the endodermis, where they show extremely low turnover and block the diffusion of membrane proteins like NOD26-LIKE INTRINSIC PROTEIN5;1 and BORON TRANSPORTER1 .

How has the evolutionary history of VIT_01s0010g01870 shaped its functional specialization?

The evolutionary trajectory of VIT_01s0010g01870 provides important insights into its functional specialization in Vitis vinifera. Comparative genomic analyses reveal several key evolutionary aspects:

• Phylogenetic Position:

  • VIT_01s0010g01870 belongs to the broader CASPL family, which predates the emergence of true CASPs

  • The protein shows homology to MARVEL domain proteins found across eukaryotes, suggesting ancient origins of the four-transmembrane scaffold structure

• Structural Evolution:

  • The core transmembrane domains show high conservation with both plant CASPLs and non-plant MARVEL proteins

  • Conserved basic (Arg, His, Lys) and acidic (Asp, Glu) amino acids in TM1 and TM3 are shared features between CASPLs and MARVELs, indicating functional importance

• Functional Diversification:

  • Unlike specialized CASPs that form the Casparian strip in the endodermis, VIT_01s0010g01870 likely has diversified functions in grapevine

  • The absence of the nine-amino acid signature found in spermatophyte CASPs suggests it may not participate in endodermis-specific functions

This evolutionary context suggests that VIT_01s0010g01870 represents a more generalized membrane scaffold protein that might form specialized membrane domains in Vitis vinifera, potentially involved in cell wall modifications distinct from the Casparian strip formation seen in Arabidopsis .

What experimental approaches can determine if VIT_01s0010g01870 functions are conserved across plant species?

To establish whether the functions of VIT_01s0010g01870 are conserved across plant species, several complementary experimental approaches should be employed:

• Heterologous Expression Studies:

  • Express VIT_01s0010g01870 in model systems like Arabidopsis under control of endogenous CASP promoters

  • Test whether VIT_01s0010g01870 can rescue Arabidopsis casp mutant phenotypes

  • Compare localization patterns with endogenous CASPs using fluorescent fusion proteins

• Reciprocal Complementation:

  • Express Arabidopsis CASPs in Vitis vinifera systems to assess functional equivalence

  • Analyze whether chimeric proteins (with domains swapped between VIT_01s0010g01870 and AtCASPs) retain functionality

• Promoter Analysis:

  • Investigate whether the regulatory elements governing VIT_01s0010g01870 expression are conserved with those of CASP genes in other species

  • Test the activity of the VIT_01s0010g01870 promoter in heterologous systems

Previous research with Lotus japonicus CASP homologs demonstrated that a 2-kb genomic fragment upstream of the translational start codon was sufficient to drive endodermis-specific expression in Arabidopsis, suggesting conservation of regulatory elements . Similar approaches could determine whether VIT_01s0010g01870 shares this regulatory conservation or has evolved distinct expression patterns in grapevine.

What are the optimal experimental conditions for analyzing membrane domain formation by VIT_01s0010g01870?

Establishing optimal experimental conditions for analyzing membrane domain formation by VIT_01s0010g01870 requires careful consideration of multiple parameters:

Expression System Selection:

• Plant cell culture systems (preferably Vitis vinifera-derived) maintain native membrane composition

• Arabidopsis protoplasts offer a well-characterized alternative with established protocols

• Heterologous systems should include proper controls for membrane composition differences

Fusion Protein Design Considerations:

• C-terminal vs. N-terminal tags may differentially affect membrane insertion

• Linker length and composition critically influence membrane protein topology

• Spectral variants should be selected to minimize bleed-through in co-localization studies

Imaging Parameters:

• Live cell imaging vs. fixed samples (trade-offs between dynamics and resolution)

• Temporal resolution (CASP domains show initial broad membrane distribution followed by focused localization)

• Photobleaching considerations for long-term imaging

Recommended Protocol for Initial Characterization:

• Generate both N- and C-terminal fluorescent fusions (mGFP, mCherry)

• Express in both native tissue (Vitis vinifera) and model system (Arabidopsis)

• Perform time-course imaging from initial expression (6h) to steady state (48h)

• Quantify domain formation using fluorescence intensity distribution analysis

• Compare with known membrane domain markers and assess co-localization

This approach allows researchers to determine whether VIT_01s0010g01870 forms stable membrane domains similar to CASPs, which show extremely low turnover and create membrane diffusion barriers .

How can researchers accurately assess interactions between VIT_01s0010g01870 and cell wall modification enzymes?

Investigating interactions between VIT_01s0010g01870 and cell wall modification enzymes requires multiple complementary approaches:

• In vitro Interaction Studies:

  • Pull-down assays using purified VIT_01s0010g01870 and candidate enzymes

  • Surface plasmon resonance to measure binding kinetics

  • Isothermal titration calorimetry for thermodynamic parameters of interactions

• In vivo Interaction Studies:

  • Bimolecular fluorescence complementation (BiFC) to visualize interactions in plant cells

  • Förster resonance energy transfer (FRET) to measure proximity in membrane

  • Co-immunoprecipitation from native tissues followed by mass spectrometry

• Functional Impact Assessment:

  • Cell wall composition analysis in VIT_01s0010g01870 overexpression/knockout lines

  • Immunolocalization of wall modifications in relation to protein localization

  • Enzyme activity assays in the presence/absence of VIT_01s0010g01870

Experimental Design Table for Interaction Studies:

Based on studies with related CASPs, which interact with secreted peroxidases to mediate lignin deposition in Casparian strips, researchers should particularly investigate interactions with lignin biosynthesis enzymes and peroxidases in Vitis vinifera .

How might VIT_01s0010g01870 contribute to grapevine stress responses and what experimental designs can test this?

VIT_01s0010g01870, as a CASP-like protein potentially involved in membrane domain formation and cell wall modification, may play significant roles in grapevine stress responses. Several experimental approaches can test this hypothesis:

• Expression Analysis Under Stress Conditions:

  • qRT-PCR and RNA-seq to quantify VIT_01s0010g01870 expression under various stressors (drought, salinity, pathogens)

  • Promoter-reporter constructs to visualize tissue-specific expression changes

  • Proteomics to assess post-translational modifications under stress

• Functional Studies:

  • CRISPR/Cas9-mediated knockouts or RNAi lines with reduced VIT_01s0010g01870 expression

  • Overexpression lines to assess gain-of-function phenotypes

  • Complementation with wild-type vs. mutated versions to identify critical domains

• Phenotypic Characterization:

  • Cell wall composition analysis using FTIR, immunolabeling, and mass spectrometry

  • Stress tolerance assays measuring physiological parameters (water loss, electrolyte leakage)

  • Histochemical staining to visualize potential barrier functions

The research should focus on whether VIT_01s0010g01870 participates in forming diffusion barriers similar to Casparian strips, which could contribute to stress tolerance by regulating water and solute movement through plant tissues. This would be consistent with the known functions of CASPs in Arabidopsis, where they create membrane scaffolds that direct the deposition of lignin in cell walls, forming critical diffusion barriers .

What technical challenges must be overcome for successful heterologous expression of functional VIT_01s0010g01870?

Heterologous expression of functional VIT_01s0010g01870 presents several technical challenges that must be addressed:

• Membrane Protein Solubility and Folding:

  • Optimization of detergents for extraction (screen CHAPS, DDM, digitonin)

  • Co-expression with molecular chaperones to improve folding

  • Testing multiple expression temperatures (16°C, 25°C, 30°C)

• Expression System Selection:

  • E. coli systems: Codon optimization, specialized strains (e.g., C41/C43)

  • Yeast systems: Selection of appropriate promoters for membrane proteins

  • Insect/mammalian systems: Optimization of transfection/infection protocols

• Functional Verification Approaches:

  • Fluorescence-based localization assays to confirm membrane integration

  • Split-ubiquitin assays to verify protein-protein interactions

  • Liposome reconstitution to assess autonomous domain formation

Optimization Protocol Table for Expression Systems:

For initial verification of functionality, researchers should express VIT_01s0010g01870 in Arabidopsis endodermis (where CASPs normally function) and assess whether it can integrate into the CASP membrane domain, as previous studies have shown that most CASPLs can integrate into this domain when ectopically expressed .

What bioinformatic approaches are most effective for predicting VIT_01s0010g01870 interaction networks?

Predicting interaction networks for VIT_01s0010g01870 requires a multi-layered bioinformatic approach:

• Sequence-Based Methods:

  • Protein-protein interaction prediction based on primary sequence features

  • Motif identification in extracellular and cytoplasmic domains

  • Conservation analysis to identify functionally important residues across species

• Structure-Based Methods:

  • Homology modeling based on related MARVEL/CASPL structures

  • Molecular docking simulations with candidate interacting proteins

  • Molecular dynamics simulations to assess stability of predicted interactions

• Network Integration Approaches:

  • Co-expression network analysis using Vitis vinifera transcriptome data

  • Ortholog-based prediction using known CASP interaction networks

  • Gene ontology enrichment analysis of predicted interactors

Workflow for Comprehensive Interaction Prediction:

• Generate homology model of VIT_01s0010g01870 based on CASP/MARVEL structures

• Predict transmembrane topology and identify exposed interaction surfaces

• Perform large-scale docking with candidate cell wall modification enzymes

• Filter candidates based on co-expression in relevant tissues/conditions

• Validate top candidates experimentally through techniques outlined in section 4.2

Based on known CASP interactions, particular attention should be paid to potential associations with lignin biosynthesis enzymes, peroxidases, and membrane transporters that might be restricted to specific domains by VIT_01s0010g01870 scaffold formation .

How can contradictory experimental results regarding VIT_01s0010g01870 function be reconciled through methodological refinements?

When faced with contradictory experimental results regarding VIT_01s0010g01870 function, researchers should systematically address methodological variables:

• Experimental Context Factors:

  • Expression level effects (overexpression artifacts vs. physiological levels)

  • Cell/tissue type differences (heterologous vs. native environments)

  • Developmental timing (protein function may vary across developmental stages)

• Technical Variables:

  • Tag interference (size, position, and nature of fusion tags)

  • Sample preparation artifacts (fixation, membrane disruption)

  • Detection threshold limitations (sensitivity vs. specificity trade-offs)

• Standardization Approaches:

  • Establish standard operating procedures for key experiments

  • Implement quantitative controls for expression levels

  • Develop reporter systems that minimize experimental perturbation

Decision Tree for Resolving Contradictory Results:

• Categorize contradictions (localization, interaction, phenotype)

• Evaluate methodological differences between studies

• Design controlled experiments that systematically vary one parameter at a time

• Implement orthogonal techniques to verify key findings

• Consider biological context (developmental stage, tissue specificity)

When analyzing VIT_01s0010g01870 function, researchers should remember that CASP activities in forming membrane scaffolds and directing cell wall modifications can be uncoupled, as formation of the CASP domain is independent from lignin deposition. Similarly, interactions between CASPs and peroxidases can occur outside their native domains when ectopically expressed . These aspects may explain apparently contradictory results observed in different experimental setups.