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    Immunoblotting using precast gels

    Francisco Bustos

    Published: 2024-08-09 DOI: 10.17504/protocols.io.14egn6j8pl5d/v1
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    Abstract

    Immunoblotting is a key technique to visualize changes in protein levels upon treatments. This technique can be challenging and established procedures are required to ensure reproducibility. Here we present our optimized protocol for immunoblotting of protein samples using precast gels and semiwet transfer. This protocol can be used to analyze samples from cell extracts and from in vitro reactions.

    Steps

    Sample preparation

    1.

    Mix and in a 7:3 ratio (for example: 70µL LDS sample buffer and 30µL of Reducing Agent).

    2.

    In a 1.5 mL microcentrifuge tube add the following reagents in order: LDS sample buffer/Reducing Agent mix, IPMS lysis buffer, protein sample. For example.

    AB
    10 or 15 microliters5 microliters
    207
    3010
    3.

    Poke hole in top of 1.5 mL microcentrifuge tube with a hypodermic needle.

    4.

    Boil samples at 95°C for 0h 5m 0s using a ThermoMixer F1.5.

    Equipment

    ValueLabel
    Eppendorf ThermoMixer F1.5NAME
    ThermoMixerTYPE
    EppendorfBRAND
    5384000020SKU
    5.

    Centrifuge for 0h 0m 10s in a Mini Centrifuge at Room temperature

    Equipment

    ValueLabel
    Fisherbrand Mini-CentrifugeNAME
    CentrifugeTYPE
    FisherbrandBRAND
    12-006-901SKU
    6.

    Samples can be stored at -20°C until the day of running SDS-PAGE electrophoresis.

    SDS-PAGE Electrophoresis

    7.

    Prepare 500mL 1X MES-SDS Buffer (50millimolar (mM) MES, 50millimolar (mM) Tris Base, 0.1Mass / % volume SDS, 1Mass / % volume EDTA, pH 7.3) by diluting stock 1:20 in Milli-Q water.

    8.

    Unpack a and remove protective tape and comb.

    9.

    Assemble gel running tank by placing gel in the tank in front of the buffer core and a second gel or a buffer dam behind the

    buffer core. Lock the gel tension wedge in place. Add 1X MES-SDS buffer between the gels and outside the buffer core.

    10.

    Load 8µL protein molecular weight marker . If needed load 2µL at the end of the gel.

    11.

    Load samples to a maximum volume of 20µL.

    12.

    Place gel tank lid and connect to power supply matching colors (for positive and negative).

    13.

    Run gel at 150 V for 2h 0m 0s at Room temperature or as needed depending on the protein molecular weight and desired separation.

    Transfer

    14.

    Prepare 12X transfer buffer:

    • 58 g Tris base
    • 190 glycine
    • Milli-Q water up to 2L
    15.

    Prepare 2.5 L of 1X transfer buffer (48millimolar (mM) Tris, 39millimolar (mM) Glycine, 20% (v/v) Methanol) by mixing 212mL 12X Transfer buffer with 1788mL milli-Q water and 500mL Methanol.

    16.

    Cut or membrane to the required gel size (usually 9x7 cm) and activate PVDF membrane by incubating in methanol for at least 0h 1m 0s.

    Note
    Do not put Nitrocellulose membrane in methanol

    17.

    Cut to the required gel size (usually 9x7 cm).

    18.

    Prepare . If dirty, boil in warm tap water in the microwave for 0h 5m 0s. Soak sponge pads in 1X transfer buffer in a plastic tray.

    19.

    Remove the gel from the cassette by separating the cassette plates with a . Using the gel knife, cut off the bottom part and wells of the gel as needed.

    20.

    Place gel in a plastic tray with 1X transfer buffer.

    21.

    Make transfer sandwich inside the cathode core of the blot module in the following order:

    • 2 sponge Pad
    • 1 filter paper + gel (grab this from transfer buffer tray), Remove air bubbles by carefully rolling a on top of the gel.
    • 1 presoaked PVDF or Nitrocellulose membrane. Remove air bubbles using the Blot Roller.
    • 1 filter paper. Remove air bubbles using the Blot Roller.
    • Sponges up to fill cavity (6-7 total)
    22.

    Close blot module with the anode core and place this in the buffer chamber. Lock the blot module using the gel tension wedge.

    23.

    Place lid and connect to power supply matching colors (for positive and negative).

    24.

    Run gel at 35 V for 1h 30m 0s at Room temperature .

    25.

    Unlock blot module by releasing the tension wedge and remove from buffer chamber. Remove membrane from the sandwich and cut excess membrane using scissors.

    26.

    Incubate membrane in in a plastic tray for 0h 5m 0s with shaking in a rocking shaker.

    Equipment

    ValueLabel
    Rocking ShakerNAME
    ShakerTYPE
    OhausBRAND
    30391966SKU
    27.

    Wash with milli-Q water 3 times, quick washes. Image in Chemidoc MP if needed.

    Equipment

    ValueLabel
    ChemiDoc™ MP Imaging SystemNAME
    Imaging SystemTYPE
    Bio-radBRAND
    12003154SKU
    http://www.bio-rad.com/LINK

    Blocking

    28.

    Make 1X TBS-T (Tris buffer saline-Tween 20: 20millimolar (mM) Tris-HCl pH=7.4, 100millimolar (mM) NaCl, 0.1% (v/v) Tween-20).

    For 1L:

    • 20mL 1Molarity (M) Tris pH=7.4
    • 20mL 5Molarity (M) NaCl
    • 1mL Tween-20
    • Milli-Q water up to 1L
    29.

    Make Blocking solution: 1X TBS-T 5% skimmed milk:

    • 12.5g powder skimmed milk .
    • Fill up to 250mL with 1X TBS-T.
    30.

    Add Blocking solution to a Western Blot box and place the membrane in this solution. Incubate in a rocking shaker for at least 1h 0m 0s at Room temperature

    Primary antibody

    31.

    Prepare antibody in 1X blocking solution (for HRP detection) or in TBST 5Mass / % volume BSA (for infrared detection) at the desired concentration.

    32.

    Discard blocking solution from Western blot box and replace by diluted antibody. Incubate at 4°C 1h 0m 0s in rocking shaker.

    33.

    Next day recover antibody in tube and wash membrane 3 times for 0h 5m 0s with 1X TBS-T

    Secondary antibody

    34.

    Prepare HRP or fluorescently labelled secondary antibody in blocking solution or TBST respectively.

    35.

    Add diluted secondary antibody to Western blot box a incubate at Room temperature for 1h 0m 0s in rocking shaker.

    36.

    Wash membrane 4 times for 0h 5m 0s with 1X TBS-T

    37.

    Image in Chemidoc MP for HRP detection or LI-COR Odyssey FC imager for infrared detection.

    Equipment

    ValueLabel
    ChemiDoc™ MP Imaging SystemNAME
    Imaging SystemTYPE
    Bio-radBRAND
    12003154SKU
    http://www.bio-rad.com/LINK

    Equipment

    ValueLabel
    Odyssey CLxNAME
    Imaging SystemTYPE
    LI-CORBRAND
    Odyssey CLxSKU
    38.

    Membrane can be stored up to a week at 4°C until performing stripping.

    Stripping

    39.

    Prepare Stripping buffer:

    • weight 15g glycine
    • Dissolve in 800mL milli-Q water
    • Adjust pH to 2.2
    • add 1g SDS
    • 10 mL Tween 20
    • Bring volume up to 1 L with milli-Q water
    40.

    Incubate membrane 0h 10m 0s with stripping buffer in rocking shaker at Room temperature.

    41.

    Repeat step 37

    42.

    Wash twice with TBST

    43.

    and probe with a different antibody.

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