Expression of plant protein in Ecoli - (Mar/31/2015 )

Hello! 

I'm trying to purify plant protein expressed in Ecoli. There are two mitotic kinases, the one I'm doing now is from Arabidopsis, inserted to pdest15 vector. I transformed  E-coli C-43 pLysS by electroporation and selected transformants using ampicilin and chloramphenicol. I culture 1L of cells with antibiotics till OD is 0.6-0.8, then add IPTG to final concentration 1mM and continue culture o/n at 16C. The protein have low expression - that's why long induction time. Next I do sonication, centrifugation and use supernatant in AKTA with GSTrapFF column --> SDS-PAGE to check results. The column and AKTA protocol seem to be fine - I checked with other GST-protein, it worked. But with this one it fails. The most confusing thing is - somebody in the lab used the same protocol and it worked. I myself had used same protocol for another plant kinase - it also worked. I made new IPTG stock, it didn't help. 

Any ideas, please, I'm lost 

are you sure your protein is not in the pellet (inclusion bodies)?

if it's not, then you might try inducing at a higher temperature.