Mo,
Just to add my 50 cents, I didn't see any mention of the use of
fusion proteins in your original post. GST, MBP or my personal, and
completely biased, favourite SUMO (plus many more proteins) have been
shown to enhance expression when fused to the amino terminus of a target
protein. If you fear you have toxicity, simply tracking the OD600 pre
and post induction normally tell you if this is happening. I've worked
with proteins that basically baselined the cell growth upon induction
and, as Artem stated, at least I knew my protein was being made albeit
at very low levels.
Stephen
--
Stephen Weeks, Ph. D.
Drexel University College of Medicine
Department of Biochemistry and Molecular Biology
Room 10102 New College Building
245 N. 15th St.
Philadelphia, PA 19102
Phone: (+) 215-762-7316
Fax: (+) 215-762-4452
Mo Wong wrote:
I thought I'd post this to the CCP4bb, as judging by previous posts,
it seems I could get some useful insight into my problem...
This is question has probably been asked by people for a long as
molecular biology has been around, but hopefully my question isn't a
complete rehash of other peoples: I am trying to express a human
protein in bacteria where the only modified amino acids are 3
phosphorylated serines. I’ve gone through the usual hoopla of trying
to get it expressed in E. coli (Rosetta/Codon+ cells, varying IPTG,
low temperature, etc). Sequencing confirms my insert is correct, but
from coomassie gel inspection, I appear to get near zero induction (I
need to do a Western to get a clearer assessment). I’ve heard about
custom gene synthesis, and it appears Mr. Gene
(https://www.mrgene.com/) would be a good avenue to look into as they
optimize the ORF taking into account codon usage in E. coli (though
I’m not sure they examine putative mRNA substructure formation like
some companies do). It’s only 49c per base pair, so doesn’t seem too
cost prohibitive. My only concern is that if this protein is toxic, I
could be wasting money.
So I was wondering, has anyone seen the expression for a particular
protein change from zero in Rosetta/Codon+ cells using "native"
sequeneces to being largely overexpressed in BL21(DE3) cells using
codon optimized sequences? For folks who have had a similar problem to
the one I've described, would you recommend that I first try using a
codon optimized sequence in E. coli over testing protein expression in
yeast/insect cells, or the other way round?
Thanks!
