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How to distinguis soluble from insoluble recombinant proteins produced in E. col - (Jul/02/2012 )

Hii! I am gonna transform E.coli with a plasmid to express the protein and I need to know whether it is soluble or insoluble. I know that I should open the cells, separate soluble and insoluble fractions by centrifigation and load each on the SDS polyacrylamide gel. But I would truly appreciate if anyone could give me an effective protocol to do that.



My suggestion (the way I had done before): Grow your cells in 25 -50 ml LB culture and induce the protein expression for 2-4 hours at a OD600 = 0.6. Then take a 1.5 ml to 2 ml sample and pellet the cells. Resuspend the cells in lysis buffer (e.g. 200 µl): protein buffer + lysozyme (check out for concentration, it's been a long time when I did it so I can't remember) + Dnase. Incubate for 30 min on ice. Then freeze-thaw the cells (freeze in liquid nitrogen, thaw at room temperature) and repeat this 3 - 5 times. Then spin for ~ 30 min at 4°C, and transfer the supernatant in a new eppi. Then you can resuspend the pellet = insoluble fraction in SDS loading buffer and dilute the supernatant = soluble fraction with loading buffer. Run a SDS-Gel. It depends on the amount of protein if SDS-PAGE is enough or if you need to do a western blot.
I hope I haven't forgotten any step. It worked fine for me and I could start with the 1 L culture...