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#protein tags

3 public questions tagged with this topic.

Blotting Techniques

Which tag allows bioluminescent detection?

Bioluminescent tagging employs luciferase enzymes that generate photons through substrate oxidation without requiring external illumination, thereby avoiding autofluorescence and photobleaching. Firefly luciferase uses D-luciferin, ATP, magnesium, and molecular oxygen to produce light near 560 nm. In blotting context, target protein fused to luciferase or detected by luciferase-conjugated secondary antibody emits light captured by sensitive detectors. Alkaline phosphatase with BCIP/NBT and horseradish peroxidase with TMB produce colorimetric precipitates, while green fluorescent protein requires excitation by blue light to fluoresce. Luciferase therefore provides true bioluminescent detection with high sensitivity.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Protein-Protein Interaction

Which of the following is a pull-down tag?

Pull-down assays isolate interacting partners using affinity tags fused to bait protein. Glutathione S-transferase is a 26 kDa tag that binds with high affinity to immobilized glutathione on agarose or sepharose beads. GST-tagged bait is expressed recombinantly, captured on resin, then incubated with prey lysate. After washing, complexes are eluted using reduced glutathione. GST offers good solubility enhancement and simple purification. Unlike GFP which is fluorescent tracer and EDTA which is chelator, GST functions as both solubility and affinity handle.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Hybridization

TAP tags contain:

Tandem Affinity Purification tag is a bipartite fusion construct designed for sequential affinity capture and high-purity complex isolation under native conditions. It traditionally comprises two IgG-binding domains of Protein A from Staphylococcus aureus separated by a TEV protease cleavage site from Calmodulin Binding Peptide. First affinity utilizes Protein A binding to IgG matrix, then TEV cleavage releases complex, followed by second capture on calmodulin resin in presence of calcium. It does not contain DNA probes, RNA tags, or fluorescent proteins, which serve different purposes in detection or nucleic acid applications.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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