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    EXPRESSION AND PURIFICATION OF HUMAN NEMO (GST-GFP-NEMO)

    Elisabeth Holzer

    Published: 2023-07-31 DOI: 10.17504/protocols.io.261gedpojv47/v1
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    Abstract

    This protocol describes how to express and purify human NEMO (IKK-γ) tagged N-terminally with GST and EGFP. The expression is performed with E. coli Rosetta pLysS cells. The protein is purified via a GST batch purification and gel filtration (SEC).

    Before start

    Lysis Buffer:

    50 mM HEPES pH 7.5

    300 mM NaCl

    2 mM MgCl2

    Freshly added: 2 mM β-Mercaptoethanol, Roche Protease Inhibitor (Merck, #5056489001), and DNAse I (Sigma, #DN25-1G)

    Wash Buffer 1:

    50 mM HEPES pH 7.5

    300 mM NaCl

    Freshly added: 1 mM DTT

    Wash Buffer 2:

    50 mM HEPES pH 7.5

    700 mM NaCl

    Freshly added: 1 mM DTT

    SEC Buffer:

    25 mM HEPES pH 7.5

    150 mM NaCl

    Freshly added: 1 mM DTT

    Steps

    Expression

    1.

    Grow E. coli Rosetta (DE3) pLysS cells in 2L LB medium at 37°C until achieving an OD600 nmof 0.4.

    2.

    Reduce temperature to 18°C and continue growth to OD600 nmof 0.8.

    3.

    Induce protein expression with 250micromolar (µM) IPTG and continue growth for ~16h 0m 0s at 18°C

    4.

    Centrifuge the cells at 3000 rcf (4°C ,0h 15m 0s )

    5.

    Aspirate media and resuspend cell pellet in ~ 10 ml of 1X PBS, centrifuge the cells at 3000 rcf (4°C ,0h 15m 0s ) and take off the supernatant.

    6.

    Flash freeze the pellet in liquid nitrogen and store at -80°C until use.

    6.

    Purification

    7.

    Thaw pellet and resuspend in Lysis Buffer with freshly added 2millimolar (mM) β-Mercaptoethanol, Roche Protease Inhibitor and DNAse I

    8.

    Sonicate sample 0h 0m 30s at 65% power for 5 cycles (Bandelin Sonopuls)

    8.1.

    Repeat sonication for a total of 3X

    9.

    Centrifuge at 48000 rcf at 4°C for 0h 45m 0s

    9.1.

    During this step, equilibrate 3mL Glutathione Sepharose 4B beads by washing the slurry with water and Wash Buffer 1 (~ 6 ml).

    10.

    Filter supernatant after centrifugation through a 0.45 µm syringe filter

    11.

    Incubate the sample on equilibrated beads on a tube roller at 4°C for 4h 0m 0s

    12.

    Wash beads 5X with Wash Buffer 1

    13.

    Wash beads 1X with Wash Buffer 2

    Note
    These wash steps remove nonspecific proteins

    14.

    Wash beads 2X with Wash Buffer 1

    Note
    These washes remove high salt concentration

    15.

    Cleave the resulting sample to produce GFP-NEMO by incubating with thrombin 4h 0m 0s at 4°C

    16.

    Centrifuge beads at 3000 rcf for 0h 3m 0s at 4°C

    17.

    Collect supernatant and filter through .45 µm syringe filter

    18.

    Concentrate product to a final volume of 500µL using a 10 kDa MWCO concentrator

    19.

    The concentrated and filtered protein can be applied onto a Superose 6 increase column (10/300 Cytiva) pre-equillibrated with SEC buffer

    Note
    This step can remove contamination and degradation products

    20.

    Fractions containing the purified proteins are pooled, concentrated, frozen in liquid nitrogen and stored at - 80°C

    Note
    Protein purity can be determined by SDS PAGE analysis and measurement of protein concentration

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