Recombinant Schizosaccharomyces pombe Uncharacterized membrane protein C4.01 (SPBC4.01)

What is SPBC4.01 protein and what organism does it come from?

SPBC4.01 (dni2) is an uncharacterized membrane protein found in the fission yeast Schizosaccharomyces pombe. This protein consists of 248 amino acids and is encoded by the dni2 gene. S. pombe has been extensively used as a model organism for studying eukaryotic cell cycle regulation, making its proteins valuable for understanding fundamental cellular processes. The full protein sequence is available, beginning with MERGTSKFSWIGLVARIYNYIPHPSIFSNAILG and continuing through to QYFICKDY, as indicated in the product specifications .

What are the known structural features of SPBC4.01?

Based on available data, SPBC4.01 is a membrane protein with hydrophobic regions consistent with transmembrane domains. The amino acid sequence (MERGTSKFSWIGLVARIYNYIPHPSIFSNAILGIAWLFLIFLCCSCLTKSSIFARLLRVK NETTTVDVGFFGVCDQAINSTSRVCHELRNWDQTTGGLAYETSRFAWLQVHPVLLAIVVV FSTLSIVLTILKYLAPAYIRQWSISCLTTSTAACLLLALQMALAHISANSYAVGMNLTGK ATAKFGVAAAVFGWISSGFFLLFSLIHLGLWTIERNKQKLFEETSLSFSFITTKLRLIET QYFICKDY) suggests multiple transmembrane helices typical of integral membrane proteins . Secondary structure prediction tools would likely identify several hydrophobic regions that span the membrane, though detailed structural studies using X-ray crystallography or cryo-EM have not been extensively reported for this protein.

Why is the recombinant form of SPBC4.01 useful for research?

The recombinant form of SPBC4.01 with an N-terminal His-tag provides researchers with a purified version of the protein that can be used for multiple experimental applications. The His-tag allows for efficient purification using metal affinity chromatography and facilitates detection using anti-His antibodies. This recombinant protein enables studies on protein-protein interactions, antibody generation, enzymatic activity assessment, and structural analyses that would be difficult to perform with endogenous protein from yeast cells. Moreover, expressing the protein in E. coli overcomes challenges related to low natural expression levels in S. pombe .

What are the optimal storage conditions for recombinant SPBC4.01?

For optimal preservation of recombinant SPBC4.01 activity, the lyophilized protein should be stored at -20°C/-80°C upon receipt. After reconstitution, working aliquots can be stored at 4°C for up to one week, but repeated freeze-thaw cycles should be avoided as they can damage protein structure and function. For long-term storage, it is recommended to add glycerol to a final concentration of 5-50% (with 50% being the default recommendation) and store aliquots at -20°C/-80°C. This prevents freeze-thaw damage and maintains protein stability .

How should recombinant SPBC4.01 be reconstituted for experimental use?

For proper reconstitution of SPBC4.01:

• 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% for stability

• Aliquot the reconstituted protein to minimize freeze-thaw cycles

• Store aliquots at -20°C/-80°C for long-term use

The protein is supplied in a Tris/PBS-based buffer containing 6% Trehalose at pH 8.0, which helps maintain stability during lyophilization and reconstitution .

What expression systems are suitable for SPBC4.01 production?

• Potential toxicity to host cells

• Protein misfolding or aggregation

• Limited yield due to membrane insertion requirements

For research requiring native-like post-translational modifications or studying protein interactions in a eukaryotic context, alternative expression systems might include:

• Yeast expression systems (particularly S. cerevisiae or native S. pombe)

• Insect cell systems (Baculovirus)

• Mammalian cell expression systems

Each system offers different advantages in terms of protein folding, post-translational modifications, and functional activity.

How can SPBC4.01 be used in studies of cell cycle regulation in S. pombe?

S. pombe is an excellent model for studying eukaryotic cell cycle regulation . While SPBC4.01 (dni2) is currently uncharacterized, its potential role in cell cycle regulation can be investigated through:

• Temporal expression analysis - determining if SPBC4.01 exhibits cell cycle-dependent expression patterns similar to known cell cycle-regulated genes like cdc15, fin1, mid1, and plo1

• Co-immunoprecipitation experiments - using the recombinant His-tagged protein to identify interaction partners involved in cell cycle progression

• Localization studies - tracking the subcellular distribution of SPBC4.01 throughout the cell cycle using fluorescently tagged versions

• Gene knockout/knockdown experiments - assessing phenotypic effects of SPBC4.01 deletion on cell cycle progression

• Phosphorylation state analysis - determining if SPBC4.01 is subject to cell cycle-dependent post-translational modifications

These approaches would help position SPBC4.01 within the broader context of S. pombe cell cycle regulatory networks.

What analytical techniques are most appropriate for studying membrane protein interactions of SPBC4.01?

Given that SPBC4.01 is a membrane protein, specialized techniques are required to study its interactions:

• Detergent-based solubilization and co-immunoprecipitation:

  • Optimize detergent type and concentration for SPBC4.01 solubilization

  • Use His-tag for pull-down assays to identify interacting proteins

  • Validate interactions using reverse co-IP and mass spectrometry

• Membrane yeast two-hybrid (MYTH) system:

  • Split-ubiquitin based approach specifically designed for membrane proteins

  • Allows detection of interactions in their native membrane environment

• Crosslinking mass spectrometry:

  • Identifies proximal protein regions through chemical crosslinking

  • Particularly useful for transient interactions

• Förster resonance energy transfer (FRET):

  • Measures protein-protein proximity in live cells

  • Requires fluorescent protein tagging without disrupting function

• Surface plasmon resonance (SPR):

  • Quantitative measurement of binding kinetics

  • Requires immobilization of purified recombinant SPBC4.01

Each technique has specific advantages and limitations when working with membrane proteins like SPBC4.01.

How does SPBC4.01 relate to nitrogen sensing in S. pombe?

The alternate name "Delayed minus-nitrogen induction protein 2" (dni2) suggests a potential role in nitrogen sensing or response pathways in S. pombe . To investigate this relationship, researchers could:

• Analyze expression patterns of SPBC4.01/dni2 under varying nitrogen conditions

• Compare with known nitrogen-responsive genes

• Examine phenotypes of dni2 deletion mutants during nitrogen starvation

• Investigate protein localization changes in response to nitrogen availability

• Identify potential regulatory elements in the dni2 promoter related to nitrogen response

This research direction could reveal connections between SPBC4.01 and important cellular processes like mating, meiosis, and sporulation that are triggered by nitrogen limitation in fission yeast.

What are the potential challenges in expressing SPBC4.01 in heterologous systems?

Expressing membrane proteins like SPBC4.01 presents several challenges:

• Protein toxicity: Overexpression of membrane proteins can disrupt host cell membrane integrity, leading to growth inhibition or cell death

• Protein aggregation: Inefficient membrane insertion may result in protein aggregation and inclusion body formation

• Improper folding: The E. coli membrane environment differs from that of S. pombe, potentially affecting protein conformation

• Limited yield: The bacterial translation machinery may struggle with eukaryotic codon usage and membrane insertion mechanisms

• Purification difficulties: Solubilizing membrane proteins requires detergents that may affect protein stability and function

Optimization strategies include:

• Codon optimization for E. coli expression

• Using specialized E. coli strains (C41/C43) designed for membrane protein expression

• Testing different fusion tags beyond His-tag (MBP, SUMO, etc.)

• Expression at lower temperatures (16-20°C) to slow folding and improve insertion

• Screening multiple detergents for optimal solubilization

How can protein purity be accurately assessed for recombinant SPBC4.01?

For membrane proteins like SPBC4.01, purity assessment requires specific considerations:

• SDS-PAGE analysis:

  • The primary method stated in the product specifications, with purity >90%

  • Proteins should be denatured in SDS sample buffer containing sufficient detergent

  • Silver staining provides higher sensitivity than Coomassie for detecting contaminants

• Western blotting:

  • Using anti-His antibodies to confirm identity and integrity

  • May reveal degradation products not easily visible by protein staining

• Size exclusion chromatography (SEC):

  • Assesses monodispersity and detects aggregates or oligomeric states

  • Different detergent micelle sizes must be considered in interpreting results

• Mass spectrometry:

  • Provides precise molecular weight confirmation

  • Can identify post-translational modifications and truncations

  • Requires specialized methods for membrane proteins (often combined with detergent removal)

• Functional assays:

  • Activity tests specific to the protein's known or predicted function

  • May include binding assays with predicted interaction partners

What tools can be used to predict the membrane topology of SPBC4.01?

Understanding membrane topology is crucial for functional studies of SPBC4.01. Several bioinformatic tools can be employed:

• TMHMM/Phobius/TOPCONS:

  • Predict transmembrane helices based on hydrophobicity profiles

  • Estimate the orientation of loops (cytoplasmic vs. extracellular/lumenal)

• PredictProtein/PSIPRED:

  • Predict secondary structure elements within the protein

  • Identify potential functional domains

• AlphaFold2/RoseTTAFold:

  • Modern AI-based structure prediction tools

  • Can generate potential 3D models even without solved structures

• Signal peptide predictors (SignalP):

  • Identify potential N-terminal signal sequences

  • Help determine the initial membrane insertion orientation

For experimental validation of these predictions, researchers could use:

• Cysteine accessibility techniques

• Epitope insertion and antibody accessibility

• Protease protection assays

• Green fluorescent protein (GFP) fusion reporter assays

How should researchers interpret conflicting results between in vitro and in vivo studies of SPBC4.01?

When facing discrepancies between in vitro studies using recombinant SPBC4.01 and in vivo observations in S. pombe, researchers should consider:

• Protein context differences:

  • The recombinant protein lacks the native membrane environment

  • His-tagging may affect protein function or interactions

  • Post-translational modifications present in vivo may be absent in the recombinant protein

• Experimental conditions:

  • Buffer compositions affecting protein conformation

  • Detergent effects on protein-protein interactions

  • Temperature and pH variations between experimental conditions

• Reconciliation approaches:

  • Validate key findings using multiple complementary techniques

  • Perform structure-function analyses with mutated versions

  • Use domain-specific approaches to isolate conflicting regions

  • Consider native purification from S. pombe for comparison

• Data integration strategies:

  • Develop working models that accommodate both datasets

  • Identify experimental variables that might explain discrepancies

  • Design experiments specifically to address contradictions

Careful documentation of experimental conditions is essential for meaningful comparison of results across different experimental systems.

What statistical approaches are appropriate for analyzing SPBC4.01 protein interaction data?

When analyzing protein interaction data for SPBC4.01:

• For mass spectrometry interaction studies:

  • Apply false discovery rate (FDR) corrections for multiple testing

  • Use control datasets (e.g., unrelated His-tagged proteins) to filter non-specific binders

  • Consider statistical enrichment scores like SAINT or CompPASS

  • Implement volcano plots showing enrichment vs. statistical significance

• For binding kinetics data:

  • Fit appropriate binding models (one-site, two-site, cooperative)

  • Compare models using Akaike Information Criterion or F-tests

  • Report confidence intervals for derived parameters (Kd, Bmax)

• For co-localization studies:

  • Calculate Pearson's or Mander's correlation coefficients

  • Use randomization controls to establish significance thresholds

  • Consider spatial statistics for clustering analysis

• For functional studies:

  • Apply appropriate statistical tests based on data distribution (t-tests, ANOVA, non-parametric alternatives)

  • Use multiple comparison corrections for large-scale studies

  • Consider biological replicates vs. technical replicates in experimental design

Robust statistical analysis ensures that reported interactions represent biologically meaningful relationships rather than experimental artifacts.

How does SPBC4.01 compare to homologous proteins in other species?

While specific information about SPBC4.01 homologs is limited in the provided search results, a comparative analysis approach would typically include:

• Sequence-based comparisons:

  • BLAST searches against protein databases to identify homologs

  • Multiple sequence alignments to identify conserved residues

  • Phylogenetic analysis to understand evolutionary relationships

• Structural comparisons:

  • Prediction of secondary and tertiary structures

  • Identification of conserved domains or motifs

  • Analysis of membrane topology conservation

• Functional conservation assessment:

  • Literature review of characterized homologs

  • Complementation studies to test functional interchangeability

  • Comparison of expression patterns and regulation

• Comparative expression analysis:

  • Examination of tissue/condition-specific expression of homologs

  • Analysis of developmental regulation patterns

  • Response to environmental stimuli across species

These comparative approaches can provide insights into the evolutionary history and functional significance of SPBC4.01, potentially revealing conserved roles across different organisms.

What can be learned from comparing SPBC4.01 to other membrane proteins in S. pombe?

Comparing SPBC4.01 to other well-characterized S. pombe membrane proteins can provide valuable functional insights:

• Sequence and structural comparisons:

  • Identification of shared domains or motifs with known functions

  • Analysis of membrane topology patterns common to functional classes

  • Assessment of potential post-translational modification sites

• Localization patterns:

  • Comparison with proteins of known subcellular localization

  • Co-localization studies with marker proteins for different membranes

  • Analysis of dynamic localization patterns during cell cycle or stress

• Expression profile analysis:

  • Correlation of expression patterns with functionally related proteins

  • Identification of common regulatory elements in promoters

  • Co-expression network analysis to predict functional relationships

• Phenotypic comparisons:

  • Analysis of deletion phenotypes of related membrane proteins

  • Synthetic genetic interaction profiles to identify functional relationships

  • Chemical genetic profiles to identify shared sensitivity patterns

This comparative approach can position SPBC4.01 within functional networks and provide testable hypotheses about its cellular role.

What are the most promising approaches for determining the function of SPBC4.01?

Given the uncharacterized nature of SPBC4.01, several complementary approaches could help elucidate its function:

• Comprehensive genetic analysis:

  • Gene deletion and phenotypic characterization

  • Conditional alleles for essential functions

  • Suppressor screens to identify genetic interactors

  • Synthetic genetic array (SGA) analysis to place it in functional networks

• Protein interaction mapping:

  • Immunoprecipitation followed by mass spectrometry

  • Proximity labeling approaches (BioID, APEX)

  • Membrane-specific two-hybrid screens

  • In vitro binding assays with purified recombinant protein

• Localization and dynamics studies:

  • Fluorescent protein tagging and live-cell imaging

  • Subcellular fractionation and biochemical analysis

  • Changes in localization under different conditions or cell cycle stages

• Structural biology approaches:

  • Cryo-EM structure determination

  • X-ray crystallography of soluble domains

  • NMR studies of protein dynamics

• Comparative genomics and evolution:

  • Identification of patterns of conservation and co-evolution

  • Analysis of selective pressure on different protein regions

Integrating data from these approaches would provide a comprehensive understanding of SPBC4.01 function.

How might CRISPR-Cas9 technology be applied to study SPBC4.01 function?

CRISPR-Cas9 technology offers powerful approaches for studying SPBC4.01:

• Precision gene editing:

  • Complete gene knockout

  • Introduction of point mutations to test specific residue functions

  • Creation of fluorescent protein fusions at the endogenous locus

  • Generation of conditional alleles (e.g., auxin-inducible degron tags)

• CRISPR interference (CRISPRi):

  • Targeted transcriptional repression for partial loss-of-function

  • Temporal control of gene expression

  • Tissue-specific knockdown in multicellular model systems

• CRISPR activation (CRISPRa):

  • Upregulation of endogenous gene expression

  • Analysis of overexpression phenotypes

  • Testing effects of increased expression on interacting pathways

• High-throughput screens:

  • Synthetic genetic interaction screens using CRISPR libraries

  • Chemical-genetic screens to identify conditions affecting SPBC4.01 function

  • Parallel editing of multiple genes to test combinatorial effects

• Base and prime editing:

  • Precise introduction of specific amino acid changes

  • Creation of tagged versions without exogenous DNA integration

  • Modification of regulatory regions to alter expression

These CRISPR-based approaches provide unprecedented precision for interrogating SPBC4.01 function in its native context.

What key unknowns remain about SPBC4.01 and how might they be addressed?

Despite the availability of recombinant SPBC4.01 for research, several fundamental questions remain unanswered:

• Physiological function:

  • The cellular role of SPBC4.01/dni2 remains largely unknown

  • Its connection to nitrogen sensing suggested by the name "Delayed minus-nitrogen induction protein 2" needs experimental validation

  • Its potential role in cell cycle regulation in S. pombe requires investigation

• Structure-function relationships:

  • The 3D structure has not been determined

  • The membrane topology and critical functional residues are uncharacterized

  • Post-translational modifications that may regulate activity are unknown

• Interaction network:

  • Protein-protein interactions remain largely unmapped

  • Integration with known cellular pathways is undetermined

  • Regulatory mechanisms controlling expression and activity are unclear

Addressing these unknowns will require integrated approaches combining genetics, biochemistry, cell biology, and structural biology techniques, with the recombinant protein serving as a valuable tool for in vitro studies complementing in vivo investigations in S. pombe.

What are the broader implications of understanding SPBC4.01 function for cell biology?

While SPBC4.01 is currently uncharacterized, understanding its function could have broader implications:

• Fundamental cell cycle regulation:

  • S. pombe is a key model organism for understanding eukaryotic cell cycle control

  • If SPBC4.01 is involved in cell cycle regulation, insights may translate to other eukaryotes

  • Novel regulatory mechanisms might be uncovered

• Membrane protein biology:

  • New insights into membrane protein folding, trafficking, and function

  • Potential discovery of conserved membrane protein interaction networks

  • Methodological advances for studying challenging membrane proteins

• Nitrogen sensing and cellular response:

  • The "dni2" name suggests a role in nitrogen response pathways

  • Understanding these pathways has implications for cellular adaptation to nutrient availability

  • Potential applications in biotechnology for controlling cell growth and differentiation

• Evolutionary biology:

  • Comparative analysis across species could reveal evolutionary conservation or specialization

  • Insights into how membrane protein functions diversify during evolution

  • Understanding the evolution of cellular signaling networks