Recombinant Sorghum bicolor CASP-like protein Sb07g025950 (Sb07g025950)

What is Sorghum bicolor CASP-like protein Sb07g025950?

Sorghum bicolor CASP-like protein Sb07g025950 (also known as CASP-like protein UU-1 or SbCASPLUU-1) is a member of the CASP-like (CASPL) protein family in plants. It is a transmembrane protein consisting of 181 amino acids with UniProt ID C5YHP6. The protein belongs to a larger family of Casparian Strip Membrane Domain Proteins that are involved in forming membrane domains and directing cell wall modifications in plants. The full amino acid sequence is: MTMELESQEVVVETTTAAAAARAASAAHVRTTVALRLLAFAASLAAAVVVATNRQERWGITVTFKMFAVWEAFVAINFACAAYALLTAVFVKKLVSKHWLHHMDQFTVNLQAASTAGAGAVGSVAMWGNEPSGWYAVCRLYRLYCDRGAVSLALAFVAFVAFGVASSLSRYPRAPPPPAP R .

How does Sb07g025950 relate to other CASP family proteins?

Sb07g025950 belongs to the CASP-like (CASPL) protein family, which shares evolutionary relationships with CASPARIAN STRIP MEMBRANE DOMAIN PROTEINS (CASPs). These proteins contain four transmembrane domains with conserved residues that are particularly important for protein localization and function. Phylogenetic analysis has shown conservation between CASPLs and the MARVEL protein family, with shared conserved residues primarily located in transmembrane domains. CASP proteins form membrane domains called Casparian Strip Membrane Domains (CSDs) that function as diffusion barriers in plant tissues, especially in the endodermis. Additionally, they direct local cell wall modifications, particularly lignin deposition, through interactions with secreted peroxidases .

What are the structural features of Sb07g025950?

Sb07g025950 is characterized by four transmembrane domains, which is a conserved feature among CASP and CASP-like proteins. Based on research on related CASP proteins, the second extracellular loop (EL2) contains highly conserved residues across the CASPL family, while the first extracellular loop (EL1) shows lower conservation. Of particular importance are specific conserved residues in the transmembrane domains, especially the MARVEL/CASPL conserved Asp residue in TM3, which appears essential for correct protein folding. Other key structural features include conserved cysteine residues (C168, C175) and tryptophan (W164) in EL2, which significantly affect protein localization when mutated .

What expression systems are suitable for producing recombinant Sb07g025950?

Recombinant Sb07g025950 can be successfully expressed in both prokaryotic and eukaryotic systems. E. coli is commonly used for prokaryotic expression, while mammalian cell systems can be utilized for eukaryotic expression. When expressing in E. coli, the full-length protein (1-181 amino acids) can be produced with an N-terminal His tag to facilitate purification. The choice between these expression systems depends on experimental requirements, particularly regarding post-translational modifications. The E. coli system typically provides higher yields but lacks post-translational modifications, whereas mammalian cell expression may better preserve the protein's native structure but with lower yields .

What is the recommended protocol for reconstitution of lyophilized Sb07g025950?

For optimal reconstitution of lyophilized Sb07g025950, the following methodological approach is recommended:

• Briefly centrifuge the vial prior to opening to bring contents to the bottom

• Reconstitute the protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 5-50% (50% is the default recommendation)

• Aliquot the reconstituted protein for long-term storage at -20°C/-80°C

• Avoid repeated freeze-thaw cycles as they can compromise protein integrity

• Working aliquots can be stored at 4°C for up to one week

This protocol helps maintain protein stability and functionality for experimental applications .

How can protein purity be verified after expression and purification?

The purity of recombinant Sb07g025950 can be verified primarily through SDS-PAGE analysis. Commercial preparations typically achieve purity levels of >90% for E. coli-expressed protein (as determined by SDS-PAGE) or >85% for both E. coli and mammalian cell-expressed protein. For more rigorous verification, researchers should consider combining SDS-PAGE with additional analytical techniques such as Western blotting (using anti-His antibodies if the protein contains a His-tag), size exclusion chromatography (SEC) to assess aggregation state, and mass spectrometry for precise molecular weight determination and sequence verification. For functional verification, activity assays specific to membrane proteins could be designed based on known CASP protein interactions with peroxidases or lignin deposition functions .

What are the known functions of CASP-like proteins in plants?

CASP-like proteins serve two primary functions in plants based on current research: (1) formation of membrane domains that act as diffusion barriers, and (2) direction of localized cell wall modifications. CASP proteins form specialized membrane domains called Casparian Strip Membrane Domains (CSDs) that restrict lateral diffusion of proteins and lipids across the plasma membrane. This creates compartmentalization within the plasma membrane, which is essential for maintaining cellular polarity. Additionally, CASPs interact with secreted peroxidases to mediate lignin deposition and build Casparian strips in the endodermis. These functions can be uncoupled, as formation of CASP domains occurs independently from lignin deposition. The specific functions of Sb07g025950 would likely follow similar patterns, though its precise tissue expression and localization patterns may determine its specialized roles .

How can site-directed mutagenesis be used to study Sb07g025950 function?

Site-directed mutagenesis represents a powerful approach for investigating the structure-function relationships of Sb07g025950. Based on research on related CASP proteins, key targets for mutagenesis include:

• Conserved residues in transmembrane domains, particularly the MARVEL/CASPL conserved Asp residue in TM3 (corresponding to D134 in AtCASP1), which appears essential for protein folding

• Conserved residues in EL2, including tryptophan (equivalent to W164 in AtCASP1), which significantly affects protein localization

• Conserved cysteine residues in EL2 (corresponding to C168 and C175 in AtCASP1), which affect membrane localization dynamics

The experimental approach should include:

• Generation of constructs with specific point mutations

• Fusion with fluorescent tags for localization studies

• Expression in appropriate plant systems or heterologous expression systems

• Analysis of protein localization, stability, and functional outcomes

• Complementation assays in knockout mutants to assess functional recovery

Such studies could reveal which residues are critical for Sb07g025950's localization, membrane domain formation, and interactions with peroxidases for cell wall modification .

What techniques can be used to study Sb07g025950 membrane localization?

To study the membrane localization of Sb07g025950, researchers can employ several complementary techniques:

• Fluorescent protein tagging:

  • Fusion of Sb07g025950 with fluorescent proteins (GFP, mCherry)

  • Expression in plant cells or heterologous systems

  • Confocal microscopy for visualization of subcellular localization

  • Time-lapse imaging to assess dynamic localization patterns

• Immunolocalization:

  • Generation of specific antibodies against Sb07g025950

  • Immunofluorescence microscopy in fixed tissue samples

  • Immunogold labeling combined with electron microscopy for high-resolution localization

• Membrane fractionation:

  • Differential centrifugation to isolate membrane fractions

  • Western blotting of fractions to detect protein presence

  • Detergent resistance assays to assess association with membrane microdomains

• FRAP (Fluorescence Recovery After Photobleaching):

  • Assessment of protein mobility within membranes

  • Determination of diffusion coefficients and mobile fractions

• Co-localization with known membrane markers:

  • Co-expression with established markers for various membrane domains

  • Calculation of co-localization coefficients

These techniques can reveal the specific membrane domains where Sb07g025950 resides, its dynamics, and potential interactions with other membrane components .

How is Sb07g025950 related to CASP proteins across plant species?

Sb07g025950 belongs to the broader CASP-like (CASPL) protein family that is evolutionarily related to Casparian Strip Membrane Domain Proteins (CASPs). Phylogenetic analysis has revealed that CASP and CASPL proteins form a diverse family across the plant kingdom, with multiple subgroups that likely emerged through gene duplication and functional diversification. The CASP subgroup (CASPL1A) contains proteins specifically involved in Casparian strip formation in the endodermis, while other CASPL subgroups may have evolved different specialized functions in various plant tissues. Comparative genomic analyses indicate that a CASP-specific signature is present in the genomes of plants that form Casparian strips but absent in plants lacking these structures, suggesting co-evolution of the protein family with this specialized cell wall modification. Furthermore, there is conservation between CASPLs and the MARVEL protein family, with shared conserved residues primarily located in transmembrane domains .

What functional domains are conserved between Sb07g025950 and other CASP family members?

Several functional domains show conservation between Sb07g025950 and other CASP family members across plant species:

• Transmembrane domains:

  • High conservation in all four transmembrane regions

  • Particularly strong conservation of specific residues in TM3, including a critical Asp residue essential for proper protein folding

• Second extracellular loop (EL2):

  • Contains highly conserved residues across the CASPL family

  • Key residues include tryptophan (W164 in AtCASP1) and cysteine residues (C168, C175 in AtCASP1)

  • Mutations in these residues significantly affect protein localization

• CASP-specific motifs:

  • A stretch of nine residues in the first extracellular loop (EL1) is highly conserved specifically in the CASP subgroup (CASPL1A) of spermatophytes

  • This CASP-specific signature correlates with the emergence of Casparian strips in the plant kingdom

• Protein interaction domains:

  • Regions involved in interactions with peroxidases for lignin deposition

  • Domains responsible for forming higher-order complexes in membrane domains

Understanding these conserved domains provides insights into the structural basis of Sb07g025950 function and its evolutionary relationships with other CASP family proteins .

How can protein-protein interaction studies be designed for Sb07g025950?

Designing protein-protein interaction studies for Sb07g025950 requires a multi-faceted approach:

• Yeast two-hybrid (Y2H) screening:

  • Generate bait constructs with Sb07g025950

  • Screen against cDNA libraries from relevant Sorghum bicolor tissues

  • Validate interactions with targeted assays

  • Consider membrane Y2H systems optimized for membrane proteins

• Co-immunoprecipitation (Co-IP):

  • Express tagged versions of Sb07g025950 in plant or heterologous systems

  • Immunoprecipitate using tag-specific antibodies

  • Identify interacting partners by mass spectrometry

  • Validate with reciprocal Co-IP experiments

• Bimolecular Fluorescence Complementation (BiFC):

  • Fuse Sb07g025950 with one half of a split fluorescent protein

  • Fuse candidate interacting proteins with the complementary half

  • Co-express in plant cells and visualize interaction via reconstituted fluorescence

  • Map interaction domains through deletion constructs

• Proximity-dependent biotin identification (BioID):

  • Fuse Sb07g025950 with a biotin ligase

  • Express in plant cells, allowing biotinylation of proximal proteins

  • Purify biotinylated proteins and identify by mass spectrometry

• Surface Plasmon Resonance (SPR) or Microscale Thermophoresis (MST):

  • Purify recombinant Sb07g025950

  • Measure direct binding with purified candidate interactors

  • Determine binding kinetics and affinity constants

Based on what is known about CASP proteins, potential interacting partners to investigate include peroxidases involved in lignin deposition, other membrane proteins in the same domains, cell wall modification enzymes, and regulatory proteins that might control CASP-like protein localization or function .

What approaches can be used to study the role of Sb07g025950 in cell wall modification?

To investigate the role of Sb07g025950 in cell wall modification, researchers can employ several complementary approaches:

• Genetic manipulation in Sorghum bicolor:

  • Generate knockdown or knockout lines using RNAi or CRISPR/Cas9

  • Create overexpression lines with native or tissue-specific promoters

  • Develop lines expressing modified versions (point mutations, domain deletions)

• Cell wall analysis techniques:

  • Histochemical staining for lignin (phloroglucinol-HCl)

  • Autofluorescence imaging of phenolic compounds

  • Transmission electron microscopy to visualize cell wall ultrastructure

  • Immunolabeling of cell wall components

  • Comprehensive cell wall composition analysis (FTIR, NMR, mass spectrometry)

• Functional enzyme assays:

  • In vitro reconstitution of lignin polymerization with purified Sb07g025950 and peroxidases

  • Activity assays measuring lignin precursor consumption

  • Monitoring H₂O₂ consumption in peroxidase-mediated reactions

• Membrane domain visualization:

  • Fluorescent labeling of membrane domains

  • Lipid diffusion assays to assess barrier function

  • Correlative light and electron microscopy to link protein localization with cell wall modifications

• Interactome analysis focusing on cell wall modifying enzymes:

  • Co-expression analysis across tissues and developmental stages

  • Protein-protein interaction screening with known cell wall modification enzymes

  • In situ proximity ligation assays to confirm interactions in plant tissues

These approaches can provide insights into how Sb07g025950 may contribute to the spatiotemporal regulation of cell wall modifications, particularly in the context of specialized structures like Casparian strips or other lignified domains .

How can researchers investigate the membrane domain formation properties of Sb07g025950?

Investigating the membrane domain formation properties of Sb07g025950 requires specialized approaches that address the unique challenges of studying membrane compartmentalization:

• Fluorescence-based visualization techniques:

  • Express fluorescently-tagged Sb07g025950 in plant cells

  • Time-lapse imaging to capture the dynamics of domain formation

  • Super-resolution microscopy (STORM, PALM, STED) to resolve nanoscale organization

  • Single-particle tracking to analyze protein mobility within and outside domains

• Membrane diffusion barrier assays:

  • Photoactivatable or photoconvertible fluorescent protein fusions

  • FRAP (Fluorescence Recovery After Photobleaching) analysis across domains

  • Use of fluorescent lipophilic dyes to test membrane compartmentalization

  • Expression of diffusible membrane proteins to test barrier function

• Biochemical characterization of membrane domains:

  • Detergent resistance membrane fractionation

  • Lipid raft isolation and proteomics

  • Crosslinking studies to identify proteins in close proximity

  • Lipidomics of isolated membrane domains

• Heterologous expression systems:

  • Expression in systems lacking endogenous CASP-like proteins

  • Assessment of autonomous domain formation capabilities

  • Structure-function analysis using mutagenized versions

• In vitro reconstitution:

  • Incorporation of purified Sb07g025950 into artificial membrane systems

  • Giant unilamellar vesicles (GUVs) with fluorescent lipids

  • Supported lipid bilayers for high-resolution imaging

  • Assessment of protein clustering and domain formation

• Comparative studies with known domain-forming CASPs:

  • Co-expression with well-characterized CASPs like AtCASP1

  • Analysis of co-localization or competitive interactions

  • Chimeric proteins to identify domain-forming regions

These approaches would help determine whether Sb07g025950 can autonomously form membrane domains, identify the molecular determinants of this property, and characterize the biophysical properties of these domains .

What are the optimal storage conditions for recombinant Sb07g025950?

Optimal storage conditions for recombinant Sb07g025950 depend on the form of the protein and intended use duration:

• Long-term storage:

  • Store lyophilized protein at -20°C to -80°C

  • Lyophilized form maintains stability for approximately 12 months

  • Store reconstituted protein in aliquots at -20°C to -80°C with 5-50% glycerol (50% recommended)

  • Liquid form maintains stability for approximately 6 months under these conditions

• Short-term storage:

  • Working aliquots can be stored at 4°C for up to one week

  • Avoid repeated freeze-thaw cycles, which significantly decrease protein stability

• Storage buffer considerations:

  • Tris/PBS-based buffer with 6% Trehalose, pH 8.0 is recommended

  • Trehalose acts as a cryoprotectant to maintain protein structure during freeze-thaw

• Aliquoting strategy:

  • Prepare single-use aliquots to avoid repeated freeze-thaw cycles

  • Volume of aliquots should be determined based on experimental needs

These storage recommendations help maintain protein integrity, prevent aggregation, and preserve functional activity for experimental applications .

How can researchers assess the stability and activity of stored Sb07g025950 samples?

To assess the stability and activity of stored Sb07g025950 samples, researchers can employ several analytical approaches:

• Physical integrity assessment:

  • SDS-PAGE analysis to verify intact molecular weight and absence of degradation products

  • Size exclusion chromatography to detect aggregation or oligomerization states

  • Dynamic light scattering to measure particle size distribution and homogeneity

  • Circular dichroism spectroscopy to evaluate secondary structure integrity

• Functional activity assays:

  • Interaction assays with known binding partners (e.g., peroxidases)

  • In vitro lignin polymerization assays if applicable

  • Membrane incorporation efficiency in liposome or nanodisc systems

  • Oligomerization assays to assess self-association properties

• Stability monitoring over time:

  • Time-course analysis under different storage conditions

  • Accelerated stability testing at elevated temperatures

  • Freeze-thaw cycle tolerance testing

  • pH and buffer composition optimization

• Quality control benchmarks:

  • Comparison to fresh preparations or reference standards

  • Establishment of acceptance criteria for key parameters

  • Development of standardized functional assays relevant to CASP-like proteins

When designing stability assessments, researchers should consider the intended application of the protein. For structural studies, physical integrity may be paramount, while for functional studies, retention of specific activities would be the critical parameter to monitor .