Co-Immunoprecipitation Protocol Overview

Research will be limited to:
- Method: Co-immunoprecipitation
- Interaction Type: Protein-Protein
- Objective: Protocol/Procedure
- Context: Cell Lysis

Strategy: The user is looking for a comprehensive, step-by-step Co-Immunoprecipitation (Co-IP) protocol specifically for studying protein-protein interactions. I need to find detailed procedures covering all requested phases: lysis (including buffer composition and inhibitors), bead preparation/antibody coupling, washing (addressing stringency), and elution. I will look for established laboratory protocols (e.g., Nature Protocols, Cold Spring Harbor, or major reagent provider guides) to ensure technical accuracy and provide specific concentrations and incubation times.
Queries:
- standard co-immunoprecipitation protocol lysis buffer protease inhibitors bead preparation antibody coupling washing elution
- Co-IP washing stringency optimization for protein-protein interactions
- comparison of Co-IP elution methods for downstream analysis SDS-PAGE vs mass spec

🔍 Reading and summarizing 5 new websites...

1. Immunoprecipitation (IP) and co-immunoprecipitation protocol | Abcam
2. Co-immunoprecipitation (Co-IP): The Complete Guide
3. Co-Immunoprecipitation (Co-IP) Protocol | Step by Step Guide
4. Immunoprecipitation Experimental Design Tips
5. [PDF] Immunoprecipitation protocol | Abcam

Found 4 websites. Summarized content:

Immunoprecipitation (IP) and co-immunoprecipitation protocol | Abcam
Here's a co-immunoprecipitation protocol focused on cell lysis, derived from the provided website content:

Co-Immunoprecipitation Protocol for Protein-Protein Interactions (Cell Lysis Focus)

Objective: To provide a detailed protocol for co-immunoprecipitation (co-IP), specifically focusing on cell/tissue lysis for optimal protein-protein interaction studies.

Stage 1: Preparing the Lysates

• Goal: Solubilize proteins while preserving native structure and protein-protein interactions.
• Lysis Buffer Selection:
  • Use non-ionic detergents (NP-40, Triton X-100) for gentle lysis. Ionic detergents (SDS, sodium deoxycholate) can disrupt protein interactions and should be used cautiously.
  • Optimize buffer for your specific protein and sample type.
  • Include protease and phosphatase inhibitors to prevent protein degradation and dephosphorylation.
• Materials Required:
  • Suitable Lysis Buffer (e.g., ab152163 or a custom buffer)
  • Protease Inhibitor Cocktail (e.g., ab65621)
  • Phosphatase Inhibitor Cocktail (optional, e.g., ab201112)
  • PBS
  • (For tissue samples): Electric homogenizer, BioPulverizer.
• Procedure (Cell Lysates):
  1. Prepare Lysis Buffer: Choose an appropriate lysis buffer based on the protein's location.
     • NP-40 Lysis Buffer (Mild): 150 mM NaCl, 1% NP-40, 50 mM Tris-HCl pH 8.0, 0.15% BSA, 10% glycerol, protease and/or phosphatase inhibitors. Use for membrane or cytoplasmic proteins.
     • RIPA Lysis Buffer (Harsh): 50 mM Tris-HCl pH 8.0, 150 mM NaCl, 1% NP40, 0.5% sodium deoxycholate, 0.1% SDS, protease and/or phosphatase inhibitors. Use for cytoplasmic or nuclear proteins.
  2. Add Inhibitors: Add protease inhibitors (and phosphatase inhibitors if studying phosphorylated proteins) to the lysis buffer.
  3. Cell Suspension: Isolate cells and suspend them in lysis buffer. Use 300 µL buffer for 1–3 x 10^7 cells, or 600 µL for >3 x 10^7 cells. Wash cells with PBS before lysis.
  4. Lysis: Add ice-cold lysis buffer to the cell pellet and resuspend. Incubate on ice for 10 minutes (no agitation). Sonicate the lysate 3 times in ice-cold water.
  5. Clarification: Centrifuge at 8,000 x g for 10 minutes at 4°C. Collect the supernatant (lysate) and place in a fresh tube on ice.
  6. Protein Quantification: Determine protein concentration using Bradford or BCA assay. Consider cell fractionation if protein concentration is low, especially for nuclear or mitochondrial proteins.
  7. Storage: If not using immediately, snap freeze aliquots in liquid nitrogen and store at -80°C.
• Procedure (Tissue Lysates):
  1. Prepare Lysis Buffer: Same instructions as for cell lysates.
  2. Add Inhibitors: Same instructions as for cell lysates.
  3. Tissue Disruption: Snap freeze the tissue and break it up with a bead beater homogenizer before lysis, or alternatively smash frozen tissues into powder using BioPulverizer on dry ice and add 200 mg of the tissue to the bead beater tube.
  4. Lysis: Add 1200 µL of lysis buffer to the bead beater tube and homogenize for 1 min 30 secs. Remove the tubes and place them on ice for 1 minute to ensure they are cold. Add the tubes to the bead beater for a second homogenization step for a further 1 min 30 secs, then incubate on wet ice for 5 mins before spinning.
  5. Clarification: Centrifuge at 8,000 x g for 10 minutes at 4°C. Collect the supernatant (lysate) and place in a fresh tube on ice.
  6. Protein Quantification: Determine protein concentration using Bradford or BCA assay. Consider cell fractionation if protein concentration is low, especially for nuclear or mitochondrial proteins.
  7. Storage: If not using immediately, snap freeze aliquots in liquid nitrogen and store at -80°C.

Important Considerations:

• Keep samples, buffers, and equipment on ice throughout the lysis procedure.
• Optimize lysis buffer and sonication/homogenization conditions for your specific protein and cell/tissue type.
• Aseptic techniques are crucial when handling cells.
• Adjust centrifugation force and time based on cell type.

Subsequent Co-IP Steps (Brief Overview):

The protocol then proceeds with optional pre-clearing of lysates, immunoprecipitation, washing, and elution. These steps are designed to isolate the protein of interest and its interacting partners for downstream analysis (e.g., Western blotting, mass spectrometry).

Co-immunoprecipitation (Co-IP): The Complete Guide
Here's a summary of the Co-immunoprecipitation (Co-IP) protocol focusing on cell lysis, protein-protein interactions, and related elements:

Co-Immunoprecipitation (Co-IP) Protocol Summary

Co-IP is a technique for studying protein-protein interactions. It involves purifying a target protein from a complex mixture along with its interacting partners using specific antibodies immobilized on a solid bead support.

1. Sample Preparation (Cell Lysis):

• Co-IP starts with separating soluble proteins from a lysate, typically from cells or tissue.
• Tissue usually needs to be homogenized. Lysis buffer can be directly added to cell culture after washing.
• Brief sonication helps disrupt the nuclear membrane. Agitation of cells or tissue homogenate in lysis buffer for 30 minutes on ice is often sufficient to release soluble proteins.
• Insoluble material is pelleted, and the supernatant is used for Co-IP.
• Input: Reserve 1-10% of the lysate before adding antibody or beads to serve as the input control.

2. Lysis Buffers:

• Key Consideration: Whether the buffer contains ionic or non-ionic detergents.
  • Ionic detergents: (e.g., SDS, sodium deoxycholate in RIPA buffer) are strong, can disrupt protein-protein interactions, and are generally not used. They may be used for very strong protein interactions.
  • Non-ionic detergents: (e.g., NP-40, Triton X-100 at 0.1-2%) are milder, less likely to disrupt interactions, though may increase background.
  • Detergent-free buffers (EDTA in PBS) are an option for proteins released by physical disruption.
• Common Components: NaCl, Tris-HCl (pH 7.4-8, can be optimized from pH 6-9), salts (0-1 M), Mg2+ (0-10mM), and EDTA (0-5 mM).
• Temperature: Perform Co-IP at 4°C or on ice to minimize disruption of protein interactions.

3. Enzyme Inhibitors (Added Fresh):

• Protease Inhibitors: Prevent protein degradation. Examples (with typical concentrations and targets) include:
  • Aprotinin (1-10 µg/ml; serine proteases)
  • Benzamidine (15 µg/ml; serine proteases)
  • EDTA/EGTA (1-10 mM; metalloproteases)
  • Leupeptin (1-2 µg/ml; serine/cysteine proteases)
  • PMSF (0.1-1 mM; serine/cysteine proteases)
  • Pepstatin A (1-3.5 µg/ml; aspartic acid proteases)
• Phosphatase Inhibitors: Maintain protein PTMs. Examples (with typical concentrations and targets):
  • β-Glycerophosphate (1 mM; serine/threonine phosphatases)
  • Okadaic acid (10-1000 nM; protein phosphatase 1/2a)
  • Sodium fluoride (10 mM; serine/threonine phosphatases)
  • Sodium orthovanadate (1 mM; tyrosine phosphatases)

4. Bead Preparation and Antibody Coupling:

• Bead Types: Agarose or magnetic beads.
• Immobilization Methods:
  • Protein A/G: Bind to the Fc region of antibodies. Choice depends on antibody species and isotype (see Table 5 in the original document).
  • Protein L: Binds to the kappa light chain, useful for mouse and rat IgM antibodies.
  • Direct Immobilization: Covalent bonding of antibody to beads. Prevents antibody elution.
  • Biotin-Avidin Binding: Biotinylated antibody bound to streptavidin-conjugated beads.
• Immobilization protocols:
  1. Pre-immobilize the antibody to the beads before adding the lysate (direct method).
  2. Add the free antibody to the sample lysate first, then add the beads (indirect method).

5. Washing:

• Use lysis buffer, or a dedicated wash buffer, with protease and phosphatase inhibitors.
• Standard wash buffers are PBS or TBS with 0.5-1% mild detergent (NP-40 or Triton X-100).
• Increase salt (NaCl up to 1M) to increase stringency.

6. Elution:

• Elute the target protein complex from the beads.
• Common elution buffers: SDS-PAGE sample buffer (denaturing), 0.1 M glycine buffer pH 2.5-3 (non-denaturing), or urea buffer.

Co-Immunoprecipitation (Co-IP) Protocol | Step by Step Guide
Here's a summary of the Co-Immunoprecipitation (Co-IP) protocol information extracted from the provided website content, focusing on the core procedure and important considerations:

Co-Immunoprecipitation (Co-IP) Protocol Summary

• Principle: Co-IP isolates a target protein and its binding partners from cell lysates. A protein-specific antibody is incubated with the lysate. The antibody/antigen complex is captured using protein A/G-coupled agarose beads. The protein of interest is separated from the beads and analyzed, typically by Western blot.
• Protein A/G Agarose Beads: These beads bind to antibodies (particularly IgG class), facilitating the isolation of antibody/antigen complexes.

• Lysis Buffers:

  • IP Lysis Buffer: 50 mM HEPES (pH 7.5), 150 mM NaCl, 1 mM EDTA, 5 mM EGTA, 1% Tween 20, 1 mM dithiothreitol, 1 mM NaF, 100 µM PMSF.
  • RIPA Buffer: 1% v/v NP-40, 20mM Tris-HCL pH 7.4, 5mM Sodium Pyrophosphate, 5 mM EGTA, plus freshly added protease inhibitors (Leupeptin, PMSF, Sodium Ortovanadate).

• Co-IP Protocol Steps:

  1. Harvest cells and resuspend in IP lysis or RIPA buffer (with protease inhibitors) and incubate on ice (15 min).
  2. Sonicate cells (2 x 10 sec) and keep on ice.
  3. Centrifuge lysate at 10,000 x g for 10 min at 4°C, transfer supernatant to a fresh tube.
  4. Determine protein concentration using Bradford assay.
  5. Pre-clearing: Incubate lysate with A/G sepharose beads and a control IgG antibody (1-2 hr at 4C). Centrifuge to pellet beads, saving the supernatant.
  6. Immunoprecipitation: Incubate pre-cleared supernatant with specific antibody or control IgG and A/G sepharose beads overnight at 4°C.
  7. Centrifuge to pellet beads. Aspirate and discard supernatant.
  8. Wash beads multiple times (3x) with IP lysis or RIPA buffer to remove non-specifically bound proteins.
  9. Resuspend beads in 6X Laemmli buffer and boil (1 min at 100°C) to elute protein.
  10. Analyze by SDS-PAGE and Western blotting.

• Helpful Tips:

  • Lysate Preparation: Use appropriate lysis buffer (non-ionic detergents are milder than ionic). Keep samples cold and use protease/phosphatase inhibitors. RIPA is good for nuclear proteins.
  • Pre-clearing: Reduces non-specific binding to beads or the capture antibody.
  • Antibody Choice: Polyclonal antibodies offer tighter binding. Using a polyclonal for capture and a monoclonal for detection improves efficacy and specificity. Be aware of heavy and light chain bands from the primary antibody when Western blotting.
  • Wash Buffer: PBS or TBS are common. Adjust salt concentration to reduce background. Reducing agents (DTT, β-mercaptoethanol) can disrupt non-specific interactions.
  • Elution Buffer: Elute into running buffer for SDS-PAGE or use a milder buffer (0.1 M glycine, pH 2.5) followed by neutralization.

• Immunoprecipitation Crosslinking (CLIP): UV cross-linking can be used to covalently bond RNAs and proteins for studying RNA-protein interactions or RNA modifications.

• Bradford Assay: Used to determine protein concentration.

[PDF] Immunoprecipitation protocol | Abcam
Co-Immunoprecipitation Protocol for Protein-Protein Interactions, Focusing on Cell Lysis

This protocol outlines co-immunoprecipitation (Co-IP) procedures, with a focus on cell lysis for protein-protein interaction studies.

I. Cell Lysis Buffers

• General Considerations:

  • The lysis buffer should minimize protein denaturation while effectively extracting proteins.
  • Non-ionic detergents (e.g., NP-40, Triton X-100) are gentler than ionic detergents (e.g., SDS, sodium deoxycholate).
  • Optimize salt concentration (0-1M), detergent concentration (non-ionic: 0.1-2%; ionic: 0.01-0.5%), divalent cation concentration (0-10mM), EDTA (0-5mM), and pH (6-9).
  • Always add protease inhibitors immediately before use.

• Non-Denaturing Lysis Buffer:

  • Use for detergent-soluble antigens recognized in native form by the antibody.
  • Composition:
    • 20 mM Tris HCl pH 8
    • 137 mM NaCl
    • 1% Nonidet P-40 (NP-40)
    • 2 mM EDTA
  • Store up to 6 months at 4°C.

• Detergent-Free Soluble Protein Lysis Buffer:

  • For soluble proteins that may not require detergents; use with mechanical lysis (e.g., Dounce homogenizer).
  • Composition:
    • PBS containing 5 mM EDTA and 0.02% sodium azide
  • Store up to 6 months at 4°C.

• Denaturing Lysis Buffer for Non-Detergent Soluble Antigens:

  • Use when epitopes are only accessible on denatured proteins or for antigens not extractable with non-ionic detergents. DNase I is helpful.
  • Composition:
    • 1% SDS
    • 5 mM EDTA
  • Store up to 1 week at room temperature.
  • Immediately before use, add 10 mM dithiothreitol or beta-mercaptoethanol and 15 U/mL DNase I, and protease inhibitors.

II. Preparation of Lysates

• Lysates from Cell Culture (Non-Denaturing):

  1. Wash cells with ice-cold PBS.
  2. Add ice-cold lysis buffer (1 mL per 10⁷ cells/100 mm² dish/150 cm² flask; 0.5 mL per 5x10⁶ cells/60 mm² dish or 75 cm² flask).
  3. Scrape adherent cells and transfer to a pre-cooled microcentrifuge tube.
  4. Agitate for 30 min at 4°C.
  5. Centrifuge (e.g., 20 min at 12,000 rpm at 4°C – optimize).
  6. Aspirate the supernatant and transfer to a fresh tube on ice; discard the pellet.

• Lysates from Cell Culture (Denaturing):

  1. Add 100 μL denaturing lysis buffer to 0.5 – 2x10⁷ cells.
  2. Vortex vigorously (2-3 sec).
  3. Heat samples to 95°C for 5 min to denature.
  4. Dilute with 0.9 mL non-denaturing lysis buffer.
  5. Fragment DNA by passing the suspension 5-10 times through a needle attached to a 1 mL syringe.
  6. Incubate on ice for 5 min.

• Lysates from Tissue:

  1. Dissect tissue quickly with clean tools, ideally on ice.
  2. Snap freeze in liquid nitrogen and store at -80°C or keep on ice.
  3. Add ~300 μL lysis buffer per ~5 mg tissue and homogenize with an electric homogenizer.
  4. Rinse the blade twice with another 300 μL lysis buffer and agitate for 2 h at 4°C.
     *Lysis buffer volume should be determined based on the amount of tissue. Protein extract should be at a concentration between 0.1 mg/mL and 5 mg/mL.
  5. Centrifuge for 20 min at 12,000 rpm at 4°C; aspirate supernatant and discard the pellet.

III. Other Reagents

• Protease inhibitors (e.g. PMSF, aprotinin)
• Sterile PBS pH 7.4
• Sterile PBS -BSA 1% w/v (filtered)
• TBST buffer
• Loading/sample buffer for western blotting
• VeriBlot for immunoprecipitation secondary antibodies

IV. Bead Selection

• Determine the appropriate protein A or G bead based on the antibody species and isotype to ensure strong binding.

Note: This is an excerpt; the full protocol includes pre-clearing, immunoprecipitation (Methods A and B), washing, and elution steps (glycine, SDS, or urea).