SBT4.13 Antibody
Description
SBTOverview
SBT4.13 belongs to the subtilisin-like serine protease family, which plays roles in plant stress responses. Overexpression of SBT4.13 in the sbt4.13-1D mutant confers tolerance to acetic acid and oxidative stress by modulating plasma membrane H+-ATPase (PMA) activity .
Mechanism of PMA Regulation
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PMA Activity Reduction: Overexpression of SBT4.13 decreases PMA antigen levels and phosphorylation (activation) at residue T947, as shown by Western blot using α-CtAHA (C-terminal PMA antibody) and α-pT947 (phosphorylation-specific antibody) .
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Phenotypic Similarity to aha2-4 Mutant: Both sbt4.13-1D and aha2-4 (a PMA-deficient mutant) exhibit reduced membrane potential and tolerance to toxic cations (e.g., Li+, Cs+) and H₂O₂ .
Inhibitor Interactions
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SPI-1 as a Competitive Inhibitor: SPI-1 binds SBT4.13 with picomolar affinity (K<sub>d</sub> and K<sub>i</sub> values in the 10<sup>−12</sup> M range). It stabilizes SBT4.13 inhibition across a broad pH range, critical for its physiological function .
Table 1: PMA Quantification in sbt4.13-1D vs. Wild Type
| Parameter | Wild Type | sbt4.13-1D | Method |
|---|---|---|---|
| PMA Antigen (α-CtAHA) | 100% | 58% ± 7% | Western Blot |
| Active PMA (α-pT947) | 100% | 42% ± 5% | Western Blot |
Table 2: SPI-1 Inhibition Kinetics for SBT4.13
| Parameter | Value | Assay Type |
|---|---|---|
| K<sub>d</sub> | 2.3 ± 0.4 pM | Surface Plasmon Resonance |
| K<sub>i</sub> | 1.8 ± 0.3 pM | Competitive Binding |
Functional Implications
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Stress Tolerance: Reduced PMA activity in sbt4.13-1D lowers membrane potential, mitigating cation toxicity and oxidative damage .
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Non-Classical Inhibition: SPI-1 disrupts SBT4.13 via facilitated dissociation, challenging traditional competitive inhibition models .
Antibody Applications in SBTStudies
While no direct antibody against SBT4.13 is described, these tools were critical in elucidating its regulatory effects:
Unresolved Questions
Product Specs
Composition: 50% Glycerol, 0.01M PBS, pH 7.4
Target Background
Q&A
What is SBT4.13 and why are antibodies against it valuable for research?
SBT4.13 (At5g59120) is a subtilase family protease in Arabidopsis thaliana that appears to regulate plant responses to various stressors. Research indicates that SBT4.13 over-expression confers tolerance to oxidative stress, toxic cations, and organic acids . Antibodies against SBT4.13 are valuable research tools for:
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Detecting and quantifying SBT4.13 protein levels in wild-type versus mutant plants
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Studying subcellular localization of the protease
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Investigating protein-protein interactions involving SBT4.13
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Tracking changes in SBT4.13 expression during various stress responses
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Purifying SBT4.13 for biochemical characterization
SBT4.13 appears to function at the intersection of pH regulation, oxidative stress responses, and growth control pathways, making it an important target for researchers studying plant stress physiology .
What role does SBT4.13 play in plant stress responses?
Research data indicates that SBT4.13 has multiple roles in plant stress tolerance mechanisms:
The sbt4.13-1D mutant (over-expressing SBT4.13) shows decreased activation of NADPH oxidases (RBOH-D and RBOH-F) in response to intracellular acidification, resulting in reduced ROS production. This mechanism appears to be central to the growth inhibition normally observed under acidic conditions .
What detection methods can be used with SBT4.13 antibodies?
Researchers can employ several detection methods when working with SBT4.13 antibodies:
| Method | Application | Advantage | Consideration |
|---|---|---|---|
| Western blotting | Protein level quantification | Semi-quantitative comparison between samples | Requires optimization of extraction conditions to preserve protease activity |
| Immunofluorescence | Subcellular localization | Visual confirmation of spatial distribution | May require specific fixation methods to preserve membrane associations |
| Immunoprecipitation | Protein-protein interaction studies | Allows detection of in vivo complexes | Buffer conditions critical for maintaining interactions |
| ELISA | Quantitative detection | High sensitivity and throughput | Requires highly specific antibodies |
| Flow cytometry | Cell population analysis | Allows single-cell resolution | Requires cell isolation protocols |
For optimal results when studying SBT4.13-SPI-1 interactions, researchers should consider native conditions that preserve the high-affinity binding (Kd = 546 ± 155 pM) observed between these proteins .
How can researchers validate the specificity of SBT4.13 antibodies?
Validating antibody specificity is crucial for reliable research results. For SBT4.13 antibodies, comprehensive validation should include:
Researchers should also consider functional validation by testing whether the antibody can detect the SBT4.13-SPI-1 complex, which shows unique stability characteristics compared to other protease-inhibitor interactions .
What experimental approaches are most effective for studying SBT4.13-protein interactions?
Based on the unique characteristics of SBT4.13, several approaches are particularly effective for studying its interactions:
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Co-immunoprecipitation with native elution conditions: This preserves the stable SBT4.13-SPI-1 complex, which shows resistance to degradation for at least 4 hours at room temperature .
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Gel filtration followed by activity assays: This approach was successfully used to isolate and characterize the SBT4.13-SPI-1 complex, confirming both physical interaction and functional inhibition .
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Microscale thermophoresis: This technique allowed precise determination of the dissociation constant (Kd = 546 ± 155 pM) for the SBT4.13-SPI-1 interaction, confirming its high-affinity nature .
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Steady-state enzyme kinetics with tight-binding inhibitor models: When studying SBT4.13 inhibition, researchers should use the Morrison equation rather than conventional kinetics, as SPI-1 acts as a tight-binding inhibitor (Ki < 10 × [E]0) .
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Fluorescently labeled protein tracking: This approach can provide real-time information about complex formation and stability under various conditions .
How might antibodies be used to investigate the relationship between SBT4.13 and ROS production?
Research data suggests SBT4.13 inhibits ROS production by affecting NADPH oxidase activation during intracellular acidification . Antibodies could help elucidate this mechanism through:
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Comparative protein level analysis: Using anti-SBT4.13 antibodies to track changes in SBT4.13 protein levels during oxidative stress or acidification, comparing wild-type and mutant plants.
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Co-immunoprecipitation of NADPH oxidase complexes: Determining whether SBT4.13 physically interacts with RBOH-D and RBOH-F under stress conditions.
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In vitro proteolytic assays: Testing whether purified SBT4.13 can directly cleave NADPH oxidases and whether this is affected by SPI-1 inhibition.
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Subcellular co-localization studies: Using fluorescently labeled antibodies to determine if SBT4.13 co-localizes with NADPH oxidases at the plasma membrane before and after acid treatment.
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Plasma membrane protein turnover analysis: Tracking the degradation rate of NADPH oxidases in wild-type versus sbt4.13-1D plants using pulse-chase experiments with immunoprecipitation.
These approaches would help establish whether SBT4.13 directly degrades NADPH oxidases or regulates their activity through other mechanisms .
What methodological considerations are important when using antibodies to study SBT4.13 in acidification experiments?
When studying SBT4.13 in the context of intracellular acidification, researchers should consider:
| Consideration | Challenge | Recommended Approach |
|---|---|---|
| pH-dependent protein conformation | Epitope accessibility may change | Validate antibody binding across experimental pH range |
| Fixation methods | Acid treatments affect fixation | Test multiple fixatives to preserve acid-induced states |
| Timing of sampling | Acid responses are dynamic | Implement precise time-course sampling |
| Compartment specificity | Different pH in cellular compartments | Combine with compartment markers for accurate localization |
| Protein activity vs. abundance | Antibodies detect presence, not activity | Complement with activity assays |
| ROS interference | Oxidative damage to epitopes | Include antioxidants in buffers when appropriate |
| Extraction conditions | Maintaining protein interactions | Optimize buffers to preserve native complexes |
These considerations are particularly important given the evidence that intracellular acidification activates NADPH oxidases to produce ROS, and SBT4.13 appears to inhibit this pathway .
How can researchers use antibodies to detect SBT4.13 degradation of plasma membrane proteins?
Research suggests SBT4.13 affects plasma membrane proteins, particularly PMA and NADPH oxidases . Antibody-based approaches to investigate this include:
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Domain-specific antibody detection: Using antibodies targeting different domains of potential substrate proteins to map cleavage patterns.
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In vitro degradation assays: Incubating purified plasma membrane proteins with active SBT4.13 and detecting degradation products with specific antibodies.
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Comparative plasma membrane proteomics: Comparing the plasma membrane proteome of wild-type and sbt4.13-1D plants to identify proteins with altered abundance or degradation patterns.
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Pulse-chase experiments: Tracking the turnover rate of specific membrane proteins in the presence and absence of SBT4.13 over-expression.
The research data indicates that the sbt4.13-1D mutant has reduced levels of plasma membrane H⁺-ATPase (PMA), detected by both anti-C-terminal domain (α-CtAHA) and anti-phosphorylated C-terminus (α-pT947) antibodies . This suggests SBT4.13 may affect either the abundance or post-translational modification of PMA.
What approaches can be used to study the SBT4.13-SPI-1 complex formation?
The SBT4.13-SPI-1 interaction represents a high-affinity, stable protease-inhibitor complex that researchers can study using several antibody-based approaches:
Notably, the SBT4.13-SPI-1 complex shows unique stability, with SPI-1 exhibiting only a small size shift upon binding and remaining stable for at least 4 hours at room temperature . This characteristic makes it an excellent model system for studying protease-inhibitor interactions in plants.
