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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

Protein-protein interactions are important for elucidating the function of target proteins, and co-immunoprecipitation (co-IP) can easily confirm PPIs. We transiently transfected a plasmid encoding an epitope-tagged protein into HEK-293 cells and developed an immunoprecipitation method to easily confirm the binding of two target proteins.

Abstract

Protein-protein interactions (PPIs) play a pivotal role in biological phenomena, such as cellular organization, intracellular signal transduction, and transcriptional regulation. Therefore, understanding PPIs is an important starting point for further investigation of the function of the target protein. In this study, we propose a simple method to determine the binding of two target proteins by introducing mammalian expression vectors into HEK-293 cells using the polyethylenimine method, lysing the cells in homemade protein lysis buffer, and pulling down the target proteins on an epitope tag affinity gel. In addition, the PPI between the various epitope tag fused proteins can be confirmed by using affinity antibodies against each tag instead of the epitope tag affinity gel. This protocol could also be used to verify various PPIs, including nuclear extracts, from other cell lines. Therefore, it can be used as a basic method in a variety of PPI experiments. Proteins degrade by extended time course and repeated freeze-thaw cycles. Therefore, cell lysis, immunoprecipitation, and immunoblotting should be performed as seamlessly as possible.

Introduction

Proteins play a major role in all cellular functions, including information processing, metabolism, transport, decision-making, and structural organization. Proteins mediate their functions by interacting physically with other molecules. Protein-protein interactions (PPIs) are important for mediating cellular functions, such as mediating signal transduction, sensing the environment, converting energy into physical movement, regulating the activity of metabolic and signaling enzymes, and maintaining cellular organization1. Thus, PPIs can be used to elucidate unknown functions2. Methods for detecting PPIs can be classified....

Protocol

Figure 1 presents an overview of the protocol.

1. Preparation of solutions and buffers

  1. Protein lysis buffer: Prepare the protein lysis buffer following a previously published report7 (Table 1).
  2. Protein lysis buffer + protease inhibitor (PI): Add protease inhibitor (see Table of Materials) to the above-prepared buffer (step 1.1). Store at -20 °C.
  3. Sample b.......

Representative Results

Thermogenic adipocytes, also known as brown and beige adipocytes, have potential anti-obesity and anti-glucose intolerance effects. PR (PRD1-BF1-RIZ1 homologous) domain-containing 16 (PRDM16) is a transcription cofactor that plays an important role in determining thermogenic adipocyte identity9,10.

EHMT1 (euchromatic histone-lysine N-methyltransferase 1), also known as GLP, primarily catalyzes the mono- and dimethylation of ly.......

Discussion

This protocol is almost like previously reported protocols5,7,14,15. The important point of this protocol is that we never stop the experiment from the cell lysis step to the immunoprecipitation step. Protein degradation hinders PPI detection. Extended time course and repeated freeze-thaw cycles degrade proteins. Electrophoresis in SDS-PAGE should also be performed on the same day of immunoprec.......

Acknowledgements

This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number 19K18008 (G.N.), JSPS KAKENHI Grant Number 22K16415 (G.N.), JSPS KAKENHI Grant Number 22K08672 (H.O.), Japan Diabetes Society Research Grant for Young Investigators (G.N.), and MSD Life Science Foundation Research Grant for Young Investigators (G.N.).

....

Materials

NameCompanyCatalog NumberComments
0.5 M EDTA (pH8.0)Nippon gene311-90075
10% Mini-PROTEAN TGX Precast Protein Gels, 10-well, 50 µLBiorad4561034
10x Tris/Glycine/SDSBiorad1610772
ANTI-FLAG M2 Affinity GelSigmaA2220
Anti-Mouse IgG, HRP-Linked Whole Ab SheepGE HealthcareNA931-1ML
Anti-Rabbit IgG, HRP-Linked Whole Ab DonkeyGE HealthcareNA934-1ML
Cell Scraper MSumitomo BakeliteMS-93170
Collagen I Coat Dish 100 mmIWAKI4020-010
cOmplete, EDTA-free Protease Inhibitor CocktailRoche4693132001
DMEM/F-12, GlutaMAX supplementInvitrogen10565042
D-PBS (-)FUJIFILM Wako045-29795
GlycerolFUJIFILM Wako072-00626
GlycineFUJIFILM Wako077-00735
HA-Tag (C29F4) Rabbit mAb #3724Cell SignalingC29F4
Laemmli Sample bufferBio-Rad Laboratories161-0747
Micro Bio-Spin Chromatography ColumnsBiorad7326204
Mini-PROTEAN Tetra Cell for Mini Precast GelsBiorad1658004JA
Monoclonal ANTI-FLAG M2 antibody produced in mouseSigmaF3165
NaClFUJIFILM Wako191-01665
pcDNA3.1-FLAG-PRDM16This paperN/A
pcDNA3.1-HA-EHMT1This paperN/A
pcDNA3.1-vectorThis paperN/A
PEI MAX - Transfection Grade Linear Polyethylenimine HydrochloridePSI24765
Penicillin-streptomycin solutionFUJIFILM Wako168-23191
Pierce BCA Protein Assay KitThermo scientific23227
Polyoxyethylene(10) Octylphenyl EtherFUJIFILM Wako168-11805
Polyoxyethylene(20) Sorbitan MonolaurateFUJIFILM Wako167-11515
Protein G Sepharose 4 Fast Flow Lab PacksCytiva17061801
Protein LoBind Tubeseppendorf30108442
ROTATOR RT-5TAITECRT-5
skim milkMorinaga0652842 
Stripping SolutionFUJIFILM Wako193-16375
Trans-Blot Turbo Mini PVDF Transfer PackBiorad1704156B03
Trans-Blot Turbo SystemBioradN/A
Trizma baseSigmaT1503-1KG
USDA Tested Fetal Bovine Serum (FBS)HyCloneSH30910.03
VeriblotAbcamab131366
β-Actin (13E5) Rabbit mAb #4970Cell Signaling4970S

References

  1. Braun, P., Gingras, A. History of protein-protein interactions: from egg-white to complex networks. Proteomics. 12 (10), 1478-1498 (2012).
  2. Yanagida, M. Functional proteomics; current achievements. J....

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ImmunoprecipitationProtein protein InteractionsAnti epitope Tag Affinity GelBrown And Beige FatPRDM16NFIAPPARELK 1Immune Cell Adipocyte CrosstalkQuantitative PCRChromatin ImmunoprecipitationMass SpectrometryProtein DegradationHEK 293 CellsPolyethylenimineProtein Lysis BufferEpitope Tag Affinity GelNuclear Extracts

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