I am having a insert sequence attached with pelB in a pET system (pelB is signal for periplasmic expression). After induction with IPTG, I am getting better expression of protein when the cells are ultrasonicated rather than subjecting it to osmotic shock (using 20% sucrose as given in pET manual). Is it ok to use ultrasonication for proteins expressed in periplasm ?
As far as I know, there is nothing special about periplasmic proteins that makes them more sensitive to damage by sonication than other proteins. If your method is working for you to get the protein out, then why not use it?
Do freeze thaw cycles (2-3 times) and then ultra sonication and it should have no problem. We have used this approach to 10s of different protein extractions
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There is no a priori reason to think sonication would not work. Just be mindful of the temperatures generated.
As @Ishtiaq mentions freeze-thaw cycles are something to keep in mind. For a number of small globular proteins (
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