Recombinant Selaginella moellendorffii CASP-like protein SELMODRAFT_272229 (SELMODRAFT_272229)

What is CASP-like protein SELMODRAFT_272229 from Selaginella moellendorffii?

CASP-like protein SELMODRAFT_272229 is a membrane protein expressed in Selaginella moellendorffii (spikemoss), consisting of 203 amino acids. The protein contains transmembrane domains characteristic of the CASP protein family and is involved in membrane organization and cellular barrier formation. The protein features several hydrophobic regions that suggest its integration into cellular membranes, with potential roles in controlling molecular transport across these barriers. Its presence in Selaginella moellendorffii, an early vascular plant, makes it particularly interesting for studying the evolution of plant cellular compartmentalization mechanisms and barrier functions across phylogenetic lineages .

How does SELMODRAFT_272229 differ from other CASP-like proteins in the same organism?

SELMODRAFT_272229 differs from other CASP-like proteins in Selaginella moellendorffii, such as SELMODRAFT_431321 (SmCASPL2U1), primarily in its amino acid sequence, domain organization, and potentially in its specific cellular function. While both are CASP-like proteins, SELMODRAFT_272229 consists of 203 amino acids, whereas SELMODRAFT_431321 contains 204 amino acids. Their sequence identity is relatively low, suggesting divergent evolutionary paths and potentially different functional specializations.

The comparison table below highlights key differences between these two CASP-like proteins:

These differences suggest potential functional specialization between these CASP-like proteins, possibly relating to different cellular compartments or developmental stages in Selaginella moellendorffii .

What are the predicted structural features of SELMODRAFT_272229 based on sequence analysis?

Sequence analysis of SELMODRAFT_272229 reveals several key structural features characteristic of membrane proteins in the CASP family:

• Transmembrane domains: The protein contains multiple hydrophobic regions that likely form transmembrane helices. Specifically, the regions "FAAFVCCAVTMVVLITD" and "AGIGAGYTLLVLVLSIISA" show strong hydrophobicity patterns consistent with membrane-spanning domains.

• Conserved motifs: The sequence contains motifs characteristic of CASP family proteins, particularly in the regions responsible for membrane integration and protein-protein interactions.

• Predicted topology: Based on the hydrophobicity pattern, SELMODRAFT_272229 likely adopts a multi-pass transmembrane configuration with both N- and C-termini potentially oriented toward the same side of the membrane.

• Post-translational modification sites: Analysis reveals potential phosphorylation sites, particularly at serine residues, which may regulate protein function or interactions.

The protein's structural features suggest it plays roles in membrane organization and potentially in forming specialized membrane domains similar to Casparian strips in more complex vascular plants, though with adaptations specific to the evolutionary position of Selaginella moellendorffii .

How does the evolutionary conservation of SELMODRAFT_272229 inform its functional significance?

The evolutionary conservation of SELMODRAFT_272229 provides significant insights into its functional importance. CASP-like proteins are found across diverse plant lineages, from early-diverging plants like Selaginella to angiosperms, suggesting fundamental roles in plant cellular function that have been maintained throughout plant evolution.

Key aspects of evolutionary conservation include:

• Conserved domains: Specific regions within SELMODRAFT_272229 show higher conservation across species, particularly those corresponding to transmembrane domains and protein interaction sites, indicating functional constraints on these regions.

• Taxonomic distribution: The presence of CASP-like proteins in Selaginella moellendorffii, which diverged early in plant evolution, suggests these proteins emerged early in land plant evolution, potentially coinciding with the development of specialized transport barriers.

• Divergence patterns: Regions showing higher rates of evolutionary change may indicate adaptation to species-specific functions, while conserved regions likely maintain core functional properties.

• Paralog diversification: The existence of multiple CASP-like proteins within Selaginella (e.g., SELMODRAFT_272229 and SELMODRAFT_431321) indicates gene duplication events followed by functional divergence, suggesting specialized roles for each paralog.

The conservation pattern across plants positions SELMODRAFT_272229 as an important model for understanding the evolution of cellular barrier functions in the plant kingdom, potentially informing our understanding of how complex membrane specializations evolved in vascular plants .

What computational approaches are most effective for predicting SELMODRAFT_272229 interaction partners?

For predicting SELMODRAFT_272229 interaction partners, researchers should employ multiple complementary computational approaches:

• Homology-based prediction: Identify known interaction partners of CASP-like proteins in other species, particularly those with experimentally validated interactions, and evaluate whether orthologous proteins exist in Selaginella moellendorffii.

• Co-expression analysis: Analyze transcriptomic data from Selaginella moellendorffii to identify genes whose expression patterns correlate strongly with SELMODRAFT_272229, suggesting potential functional relationships.

• Domain-based interaction prediction: Use tools like DOMINE or InterPreTS to predict interactions based on known domain-domain interaction patterns, focusing on domains present in SELMODRAFT_272229.

• Structural modeling and docking: Generate 3D structural models of SELMODRAFT_272229 using homology modeling or ab initio prediction methods, then perform molecular docking simulations with potential partner proteins.

• Network-based approaches: Utilize protein-protein interaction network analysis to identify potential interaction partners based on network topology and functional enrichment.

The effectiveness of these approaches can be enhanced by integrating multiple prediction methods and applying stringent filtering criteria, such as requiring predictions to be supported by at least two independent methods. This integrated approach significantly improves prediction accuracy compared to any single method alone .

What expression systems are optimal for recombinant production of SELMODRAFT_272229?

The optimal expression system for recombinant production of SELMODRAFT_272229 depends on research objectives, particularly whether native folding and post-translational modifications are required. Based on available data and general principles for membrane protein expression:

• E. coli expression system:

  • Advantages: High yield, rapid growth, cost-effectiveness, well-established protocols

  • Recommended strain: BL21(DE3) for general expression; C41(DE3) or C43(DE3) for membrane proteins

  • Optimization: Lower induction temperature (16-20°C), reduced IPTG concentration (0.1-0.5 mM), and inclusion of membrane-stabilizing additives

  • Tags: N-terminal His-tag followed by a cleavage site improves purification without interfering with membrane integration

• Insect cell expression system:

  • Advantages: Better for complex membrane proteins requiring eukaryotic processing

  • Recommended: Sf9 or High Five cells with baculovirus vectors

  • Conditions: Infection at MOI of 1-5, harvest 48-72 hours post-infection

  • Benefits: Improved folding and potentially higher activity

• Plant-based expression systems:

  • Advantages: Native-like environment for plant proteins

  • Options: Transient expression in Nicotiana benthamiana or stable transformation in Arabidopsis cell cultures

  • Benefits: Potentially more accurate post-translational modifications

What purification strategies yield highest purity for SELMODRAFT_272229?

Achieving high purity for SELMODRAFT_272229 requires a multi-step purification strategy optimized for membrane proteins:

• Solubilization protocol:

  • Detergent selection: Begin with mild detergents such as n-dodecyl-β-D-maltopyranoside (DDM) or LMNG at concentrations slightly above their critical micelle concentration

  • Buffer composition: Tris-based buffer (20-50 mM, pH 8.0) containing 150-300 mM NaCl and 5-10% glycerol for stability

  • Solubilization conditions: 1-2 hours at 4°C with gentle rotation

• Initial purification:

  • Immobilized metal affinity chromatography (IMAC): Use Ni-NTA resin for His-tagged protein

  • Washing: Stepwise imidazole gradients (10 mM, 20 mM, 40 mM) to remove non-specific binding

  • Elution: 250-300 mM imidazole in detergent-containing buffer

• Secondary purification:

  • Size exclusion chromatography (SEC): Separates monomeric protein from aggregates and removes impurities

  • Column recommendation: Superdex 200 Increase 10/300 GL

  • Buffer: Tris-based buffer with reduced detergent concentration and 50% glycerol for stability

• Quality assessment:

  • SDS-PAGE: Confirm >90% purity

  • Western blot: Verify identity using anti-His antibodies

  • Dynamic light scattering: Assess monodispersity

Based on the storage recommendations for the related protein SELMODRAFT_431321, the purified SELMODRAFT_272229 should be stored in aliquots at -20°C/-80°C in a buffer containing 50% glycerol to prevent freeze-thaw damage. Working aliquots can be stored at 4°C for up to one week, but repeated freeze-thaw cycles should be avoided .

What analytical techniques are most suitable for studying SELMODRAFT_272229 interactions?

To comprehensively study SELMODRAFT_272229 interactions, researchers should employ multiple complementary analytical techniques:

• Co-immunoprecipitation (Co-IP):

  • Approach: Use anti-His antibodies to pull down His-tagged SELMODRAFT_272229 and identify co-precipitating proteins

  • Detection: Mass spectrometry analysis of pull-down fractions

  • Controls: Include tag-only controls and non-specific antibody controls

• Surface Plasmon Resonance (SPR):

  • Setup: Immobilize purified SELMODRAFT_272229 on a sensor chip in detergent-containing buffer

  • Analysis: Measure binding kinetics (kon, koff) and affinity (KD) of potential interaction partners

  • Advantages: Real-time, label-free detection with quantitative binding parameters

• Microscale Thermophoresis (MST):

  • Approach: Label SELMODRAFT_272229 with fluorescent dye and measure thermophoretic mobility changes upon binding

  • Benefits: Low protein consumption, works in complex buffers containing detergents

  • Analysis: Determine binding affinities in near-native conditions

• Crosslinking Mass Spectrometry (XL-MS):

  • Method: Use membrane-permeable crosslinkers like DSS or photo-activatable crosslinkers

  • Analysis: Identify crosslinked peptides by mass spectrometry

  • Output: Provides spatial constraints for interaction interfaces

• Förster Resonance Energy Transfer (FRET):

  • Setup: Create fusion constructs with appropriate fluorophore pairs

  • Analysis: Measure energy transfer as indication of proximity

  • Applications: Can be used in reconstituted systems or cellular contexts

These techniques should be applied in a complementary manner, as each provides different insights into protein interactions. For membrane proteins like SELMODRAFT_272229, careful consideration of detergent conditions is essential to maintain native-like structure while enabling analysis .

How should researchers interpret contradictory results in SELMODRAFT_272229 functional studies?

When faced with contradictory results in SELMODRAFT_272229 functional studies, researchers should follow a systematic approach to resolution:

• Methodological comparison:

  • Examine differences in experimental conditions (pH, salt concentration, detergent type)

  • Evaluate protein preparation methods (expression system, purification strategy, tag position)

  • Consider differences in assay sensitivity and specificity

• Data re-analysis:

  • Apply standardized normalization methods across datasets

  • Perform statistical reanalysis using consistent parameters

  • Consider whether contradictions are statistically significant or within experimental variation

• Molecular context assessment:

  • Evaluate whether experiments were performed in different cellular compartments

  • Consider developmental stage or tissue-specific differences

  • Assess potential post-translational modification states

• Resolution strategies:

  • Design critical experiments specifically addressing the contradiction

  • Employ orthogonal techniques that measure the same parameter through different methods

  • Develop in vitro reconstitution systems that allow precise control of all variables

• Integration framework:

When reporting contradictory results, researchers should explicitly acknowledge all observations, provide detailed methodological information, and propose testable hypotheses that could explain the discrepancies, rather than selectively reporting only consistent findings .

What statistical approaches are most appropriate for analyzing SELMODRAFT_272229 expression data?

When analyzing SELMODRAFT_272229 expression data, researchers should select statistical approaches based on the experimental design, data distribution, and specific research questions:

• For transcriptomic data analysis:

  • Normalization: Use methods appropriate for the platform (e.g., TPM, RPKM for RNA-seq)

  • Differential expression: Employ DESeq2 or edgeR for RNA-seq count data

  • Multiple testing correction: Apply Benjamini-Hochberg correction to control false discovery rate

  • Validation: qRT-PCR with appropriate reference genes stable in the experimental conditions

• For protein quantification:

  • Western blot analysis: Use housekeeping proteins for normalization and analyze band intensities with tools like ImageJ

  • Mass spectrometry: Apply label-free quantification or isotope labeling approaches

  • Statistical testing: Use paired t-tests for before/after comparisons or ANOVA for multiple condition comparisons

• For correlation analyses:

  • Co-expression: Calculate Pearson or Spearman correlation coefficients based on data distribution

  • Network analysis: Apply WGCNA (Weighted Gene Co-expression Network Analysis) for identifying modules

  • Visualization: Use heatmaps with hierarchical clustering to identify patterns

• Experimental design considerations:

  • Power analysis: Determine appropriate sample sizes based on expected effect sizes

  • Biological replicates: Minimum of 3-5 independent biological replicates

  • Technical replicates: Consider nested designs and mixed-effects models

• Advanced approaches:

  • Machine learning: Use supervised learning for pattern recognition in complex datasets

  • Bayesian methods: Apply when prior information can be incorporated or for small sample sizes

  • Meta-analysis: Combine results across multiple studies for increased statistical power

Researchers should always clearly report all statistical methods, including software versions, parameters, and thresholds used in the analysis. For SELMODRAFT_272229 studies, special attention should be paid to normalization strategies for membrane proteins, which often require different approaches than soluble proteins .

Why might recombinant SELMODRAFT_272229 show low expression levels?

Low expression levels of recombinant SELMODRAFT_272229 can result from multiple factors, each requiring specific troubleshooting approaches:

• Toxicity to host cells:

  • Symptoms: Reduced growth rate, cell lysis after induction

  • Solution: Use tightly regulated promoters, lower induction levels, or switch to specialized strains like C41(DE3) designed for toxic membrane proteins

  • Alternative: Consider cell-free expression systems that bypass toxicity issues

• Codon usage bias:

  • Issue: Rare codons in Selaginella sequence not efficiently translated in host

  • Analysis: Calculate codon adaptation index (CAI) for the sequence in your expression host

  • Solution: Optimize codons for expression host or use strains supplemented with rare tRNAs

• mRNA secondary structure issues:

  • Problem: Strong secondary structures near start codon inhibiting translation initiation

  • Analysis: Predict mRNA folding energy in the 5' region

  • Solution: Modify 5' sequence without changing amino acids to reduce secondary structure

• Protein degradation:

  • Indicators: Detection of truncated products by Western blot

  • Approach: Add protease inhibitors during extraction, reduce induction temperature

  • Modification: Include stabilizing fusion partners like SUMO or MBP

• Membrane protein-specific issues:

  • Problem: Limited membrane capacity in expression host

  • Solution: Co-express membrane integrase factors or chaperones

  • Alternative: Use milder detergents during extraction to improve recovery

Experimental approach for optimization:

Based on the successful expression of the related protein SELMODRAFT_431321 in E. coli, similar conditions might work for SELMODRAFT_272229, but systematic optimization is still necessary for each specific construct .

How can protein aggregation of SELMODRAFT_272229 be prevented during storage?

Preventing aggregation of SELMODRAFT_272229 during storage requires understanding the physicochemical properties of membrane proteins and implementing appropriate stabilization strategies:

• Optimal buffer composition:

  • Base buffer: Tris-based buffer at pH 8.0 appears suitable based on related proteins

  • Salt concentration: 150-300 mM NaCl to provide ionic strength without promoting aggregation

  • Stabilizing agents: 50% glycerol has been successfully used for the related protein SELMODRAFT_431321

  • Additives: Consider adding 1-5 mM DTT if cysteine residues are present to prevent disulfide-mediated aggregation

• Storage temperature optimization:

  • Long-term storage: -80°C in aliquots to prevent repeated freeze-thaw cycles

  • Medium-term: -20°C with adequate cryoprotectants (glycerol at 50%)

  • Short-term working solutions: 4°C for up to one week as recommended for related proteins

• Aliquoting strategy:

  • Single-use aliquots: Prepare small volumes that will be used completely once thawed

  • Concentration consideration: Higher concentrations may promote aggregation, optimal range typically 0.5-2 mg/mL

  • Container material: Use low-protein binding tubes to prevent surface-induced aggregation

• Detergent considerations:

  • Detergent concentration: Maintain detergent above CMC (critical micelle concentration)

  • Detergent stability: Some detergents precipitate at low temperatures; verify compatibility

  • Alternative: Consider using amphipols or nanodiscs for improved stability

• Quality control methods:

  • Before storage: Verify monodispersity by dynamic light scattering

  • After thawing: Perform size exclusion chromatography to separate aggregates

  • Activity testing: Develop a simple functional assay to verify protein remains active

Following the recommendations from search results, researchers should avoid repeated freeze-thaw cycles of SELMODRAFT_272229, use Tris/PBS-based buffer with glycerol, and consider protein concentration in the 0.1-1.0 mg/mL range for optimal stability .

What are the potential applications of SELMODRAFT_272229 in understanding plant evolution?

SELMODRAFT_272229, as a CASP-like protein from Selaginella moellendorffii, offers significant opportunities for understanding plant evolutionary biology:

• Evolutionary transition studies:

  • SELMODRAFT_272229 can serve as a molecular marker for studying the evolution of membrane specialization in early land plants

  • Comparative analysis with CASP proteins from bryophytes and angiosperms can reveal molecular adaptations during vascular plant evolution

  • Functional studies may provide insights into how Casparian strip-like barriers evolved during plant terrestrialization

• Molecular phylogenetics applications:

  • The sequence diversity in CASP-like proteins across plant lineages allows reconstruction of evolutionary relationships

  • Domain conservation analysis can identify functional regions maintained under selective pressure

  • Molecular clock approaches can date the emergence and diversification of these proteins

• Developmental evolution investigations:

  • Studying expression patterns across tissues can reveal how functional specialization evolved

  • Comparison with expression patterns in other plant lineages can identify conserved regulatory networks

  • Heterologous expression studies can determine functional equivalence across evolutionary distance

• Methodological approaches:

  • Ancestral sequence reconstruction to infer properties of proto-CASP proteins

  • CRISPR-based genome editing in Selaginella to create knockout lines

  • Heterologous complementation assays in Arabidopsis casp mutants

The evolutionary position of Selaginella moellendorffii as an early vascular plant makes SELMODRAFT_272229 particularly valuable for understanding the emergence of specialized membrane structures that facilitated the evolution of complex plant vasculature and water/nutrient transport systems .

How can structural biology approaches be optimized for studying SELMODRAFT_272229?

Optimizing structural biology approaches for SELMODRAFT_272229 requires specialized techniques suited for membrane proteins:

• X-ray crystallography optimization:

  • Detergent screening: Systematic testing of detergents (DDM, LMNG, OGNG) for crystal formation

  • Lipidic cubic phase (LCP): Consider LCP crystallization as an alternative to detergent-based approaches

  • Crystal engineering: Design constructs with reduced flexibility by removing disordered regions

  • Crystallization additives: Screen lipids and cholesterol derivatives that may stabilize native conformation

• Cryo-electron microscopy approaches:

  • Sample preparation: Optimize grid preparation with appropriate detergent concentration

  • Particle enhancement: Consider reconstitution in nanodiscs or amphipols to increase particle size

  • Data collection: Use technologies like Volta phase plates to enhance contrast

  • Processing: Apply specialized membrane protein-focused classification algorithms

• Nuclear magnetic resonance adaptations:

  • Selective labeling: Use amino acid-selective labeling to reduce spectral complexity

  • Solid-state NMR: Consider for full-length protein in membrane mimetics

  • Fragment approach: Study individual domains if full-length protein proves challenging

• Integrative structural biology workflow:

• Computational approaches:

  • Homology modeling: Use related structures as templates

  • Ab initio prediction: Apply AlphaFold2 with membrane-specific modifications

  • Molecular dynamics: Simulate behavior in lipid bilayers to refine structural models

These specialized approaches can overcome the challenges inherent in membrane protein structural biology and provide valuable insights into SELMODRAFT_272229 structure-function relationships .