Bacterial Expression of Motors

Materials

Expression plasmid (e.g.,pET/Ncd in BL21(DE3)pLysS host cells)

ZB = 10 g NZ-Amine A

5 g NaCl

860 ml final volume

10X M9 Salts = 1 g NH₄Cl

3 g KH₂PO₄

6 g Na₂HPO₄

100 ml final volume

M9ZB = 860 ml ZB

100 ml 10X M9 Salts

40 ml 10% glucose

1 ml 1 M Magnesium Sulfate

1 ml 50 mg/ml Ampicillin in DDW

0.1 ml 50 mg/ml Chloramphenicol in EtOH

Sterile glycerol (0.5 ml in sterile tube)

1 M IPTG,dioxane-free in DDW

200 mM PMSF in EtOH

Special Equipment

Refrigerated Incubator Shaker (e.g.,New Brunswick Innova 4330)

Procedure

1.Inoculate 1 ml of M9ZB with single colony from newly transformed cells or freshly streaked plate from glycerol culture of newly transformed cells.

2.Grow cells for 1.5 hr at 37℃.

3.Inoculate 20 ml M9ZB with the 1 ml culture and grow 1.5 hr at 37℃.

4.Inoculate 4 x 500 ml M9ZB in 2 L culture flasks with 5 ml of the culture and grow overnight (12-14 hr)at 22℃ to OD₅₅₀ = 0.9 to 1.0.

5.Sterilely withdraw 0.5 ml cells,mix with 0.5 ml sterile glycerol in a sterile tube,freeze at -80℃ for future use as stock.

6.Add IPTG to 0.4 mM to induce protein expression and shake at 22℃ for 3.5-6 hr.

7.Harvest cells by swirling in ice water bath for 5 min,transfering to centrifuge bottles on ice and centrifuging at 6,500 rpm (7,100 x g)in a Sorvall GS-3 rotor.

8.Resuspend cells in column buffer containing 0.5-1 mM PMSF and centrifuge in 30 ml tared Oak Ridge tubes.

9.Weigh tubes,should contain 2-5 g cells/tube.

10.Flash freeze in liquid N₂ and store at -80℃ until use.

Notes

1.The use of newly transformed cells or a freshly streaked plate from a glycerol culture of newly transformed cells improves protein expression.

2.To optimize induction time,grow a 20 ml culture to OD₅₅₀ = 0.9 to 1.0,withdraw 0.5 ml for 0 timepoint,then induce by adding IPTG to 0.4 mM and take 1 hr,2 hr,4 hr,6 hr and overnight timepoints.Centrifuge samples after collection for 1-2 min in a microfuge to collect cells and resuspend pellet in 30 microliters 1X SDS loading dye solution.Analyze by SDS-PAGE (5-10 microliters/lane)to determine the optimal time of induction.

3.To monitor induction of large cultures,withdraw 0.5 ml of cells from each flask just prior to induction and just prior to harvest.Centrifuge samples for 1-2 min in a microfuge and resuspend pellet in 30 microliters 1X SDS loading dye solution.Analyze by SDS-PAGE to determine if the cells are induced.

4.For biotinylated motors,grow cells in M9ZB media containing 1 µM biotin and add biotin to 2 µM at the time of induction.

5.Plasmids may be lost from cells during growth or induction.It is therefore necessary to test each batch of induced cells for protein expression.