Purification of GST-fusion proteins

Materials

LB-Medium 10g Bacto-Trypton, 5g yeast extract, 5g NaCl, pH 7.0, ad 1l A.bidest

Ampicillin 100µg/ml IPTG 100mM Isopropylthiogalactosid T-buffer 100mM Tris (pH 8.0), 5mM EDTA Lysis buffer (200 ml): 10 ml Tris pH 8.0 [1M]  50 mM 4 ml EDTA [0.5 M]  10 mM 30 ml NaCl [1M]  150 mM 40 ml Glycerol [50 %]  10 % 0.5 ml Triton [10 %]  0.025 % add freshly à 20 ml: 50 µl DTT [1M]  2.5 mM 20 µl PMSF [10 mg/ml] 20 µl Leupeptin [10 mg/ml] 20 µl Aprotenin [10 mg/ml] 20 µl Pefablock [10 mg/ml] Lysozyme 1 mg/ml Sepharose- solution. Glutathione-sepharose-solution PBS (1x) 24g NaCl, 0.6g KCl, 3.45g Na2HPO4 x 7 H2O, 0.6 g

KH2PO4, pH 7.4, ad 1l mit A.bidest.

Procedure

The frozen bacteria pellets are thawed in 5 ml T-buffer on ice and resuspended. Afterwards the samples are incubated with 1 ml lysozyme for 30 min. The cells are broken through the addition of 20 ml lysis buffer and the treatment of ultrasonic sound (impulse 50%, 20sec, 3-5x) on ice water.

300 µl sepharose-solution is added to the suspension and incubated for 10 min with head-over-head rotation. Afterwards the lysate is centrifuged for 20 min at 16000 rpm and 4°C. For purification, 1-2 ml 50% glutathione-sepharose solution (GST- Fast4Flow in T-buffer) is added to the lysate, which was washed three times with T- buffer. The sample is then incubated for 2-4 h at 4°C with head-over-head rotation. Afterwards the pellet is washed three times with 1x PBS by centrifugation at 2000 g. The supernatants (wash1-wash3) are collected each time and stored at 4°C. The success of the purification is analysed by SDS-PAGE and Coomassie-staining. The isolated, purified GST-fusion protein coupled to gluthathione-sepharose can now be used for the GST-pulldown. The remaining sample is eluted by the addition of glutathione and is stored at -80°C after dialysis.