#protein interactions

Protein-Protein Interaction

Protein microarrays can study:

Protein microarrays present thousands of individually purified human proteins, domains, or peptides immobilized in native conformation on chip. Incubation with small molecules, drugs, or chemical probes labeled or detected via antibodies reveals specific binding events across entire proteome in one assay. This enables identification of off-targets, target deconvolution, selectivity profiling, and discovery of novel druggable interactors. DNA splicing, mitochondrial translation, and gene silencing are nucleic acid processes not directly assayed by protein-only arrays, whereas drug-protein interaction screening exemplifies functional application of high-content arrays.

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

BiFC (Bimolecular Fluorescence Complementation) detects:

Bimolecular Fluorescence Complementation is a genetic technique to visualize protein-protein association in living cells. Candidate proteins are fused to non-fluorescent N- and C-terminal fragments of a fluorescent protein such as YFP or Venus. Individually fragments are non-fluorescent. When fused proteins interact, fragments are brought into proximity to refold into functional fluorophore, emitting fluorescence detectable by microscopy or flow cytometry. Irreversible complementation reports localization of interaction. It does not measure RNA cleavage, phosphorylation per se, or mismatch repair but specifically protein-protein interaction.

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 interaction is label-free and measured in real-time?

Ideal interaction analysis provides association rate, dissociation rate, and equilibrium dissociation without labeling proteins, avoiding artefacts from fluorophores or radioisotopes and enabling kinetic quantification. Surface Plasmon Resonance achieves this by optical detection of refractive index changes upon analyte-ligand binding on gold sensor chip. It operates continuously, generating sensorgrams in real-time with high sensitivity. EMSA requires labeled nucleic acid, FRET needs fluorescent fusions, BiFC relies on split fluorescent protein complementation. SPR therefore provides unbiased, label-free quantification of protein-protein binding specificity and affinity in real-time.

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

In SPR, what causes change in resonance units?

Surface Plasmon Resonance monitors binding kinetics in real-time on a gold-coated sensor chip without labels. Ligand is covalently immobilized on dextran matrix, analyte flows over. Incident polarized light excites surface plasmons; resonance angle depends on refractive index near surface. When analyte binds ligand, local mass concentration increases, altering refractive index and shifting resonance angle, recorded as resonance units versus time. Temperature fluctuations or UV are minimized and electric fields are not relevant; angle shift predominantly reflects binding-induced refractive index change.

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 not a protein interaction method?

Techniques to map physical protein associations include co-immunoprecipitation that isolates native complexes via specific antibodies, fluorescence resonance energy transfer that detects proximity under 10 nm in live cells, phage display linking phenotype to genotype, yeast two-hybrid, surface plasmon resonance, and affinity pull-downs. SDS-PAGE is a fundamental analytical separation method that denatures proteins with sodium dodecyl sulfate and resolves them by molecular weight under electric field. It provides size information but alone does not report interaction without further methods like far-western or immunoblotting for detection.

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

In a research problem, a student finds proteins A-D with gel filtration, A-C with Co-IP, and B with Y2H. What is the bes

Gel filtration separates native protein complexes by hydrodynamic size; co-elution suggests residence in same large complex but does not distinguish direct versus bridged association. Co-immunoprecipitation from lysates preserves multiprotein assemblies, confirming co-complex membership. Yeast two-hybrid tests binary, direct physical interaction inside nucleus because reporter activation requires intimate contact between bait and prey fusions independent of other yeast proteins. When protein B uniquely appears positive in two-hybrid while others co-purify only, it indicates B is the direct interactor contacting bait, while A, C, D likely associate via B.

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

What is the final output readout in yeast two-hybrid assay?

Final readout in yeast two-hybrid is based on transcriptional activation of reporter cassettes integrated downstream of Gal4-responsive promoters. If bait and prey physically associate, the activation domain is tethered to promoter, stimulating transcription of genes enabling growth on selective media lacking histidine or adenine, or colorimetric enzymes like beta-galactosidase. Thus survival, colony color, or luminescence reflects interaction strength. Fluorescence intensity, radiolabel, or sequencing are not primary outputs, although secondary validation may use them. The system converts protein interaction into a genetic readout amenable to selection.

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 is NOT a valid host for two-hybrid screening?

Classical two-hybrid relies on reconstitution of transcription factor function inside a living cell. Saccharomyces cerevisiae is the traditional host providing nuclear environment, reporter genes, and genetics. Bacterial two-hybrid adapted for E. coli uses repressor or activator reconstitution. Bacteriophage is not a cellular host but serves as display particle in phage display, not two-hybrid complementation. Although mammalian two-hybrid variants exist, standard screening for libraries is not routinely performed in human cells due to transfection efficiency and reporter complexity, making human cells non-standard for conventional yeast-based screening pipelines.

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

Which method enables studying multiple protein interactions at once?

Protein microarray format enables simultaneous evaluation of thousands of interactions on single slide, providing high-throughput advantage over pairwise methods. By immobilizing purified proteins, antibodies, or peptides in arrayed spots, one incubation with labeled probe reveals many binding events in parallel, detecting protein-protein, protein-DNA, protein-lipid, or antibody-antigen interactions. Pull-down, electrophoretic mobility shift assay, and RT-PCR are low-throughput or targeted approaches. Microarray multiplexing drastically reduces sample, time, and reagent consumption, facilitating proteome-scale network mapping, biomarker profiling, and drug screening under standardized experimental conditions.

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

What is the principle of pull-down assay?

Principle of pull-down assay centers on affinity binding between tagged bait protein and immobilized ligand, enabling capture of interacting prey proteins from mixture. Bait is expressed as fusion with GST, His, biotin, or Flag tag and retained on corresponding resin. Incubation with cell lysate allows physiological binding partners to co-precipitate via non-covalent interactions. After washing non-specific proteins, complex is eluted and analyzed by SDS-PAGE, Western blot, or mass spectrometry. Method does not depend on temperature-sensitive dyes, fluorescent resonance energy transfer, or radioactive labeling, but on highly specific tag-ligand affinity chemistry.

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

Which of the following factors stabilizes a protein's tertiary structure?

Disulfide bonds accurately describes the structural composition or molecular organization asked about in this question. In Protein Solubility, knowledge of molecular structure is directly linked to understanding biological function. The specific arrangement of chemical components in Disulfide bonds determines its physical properties, biological activity, and interactions with other molecules. The other options (High temperature, pH at isoelectric point, and High salt concentration) describe different structural arrangements, incorrect stoichiometry, or compositions of different biological molecules.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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