I am planning to purify a cytokine, and my plasmid contains a lac promoter and a periplasmic signal sequence. I am currently deciding between using BL21 (DE3) and BL21 Star™ (DE3) for protein expression. Could you advise which one might be more suitable for this purpose?
Additionally, I am wondering if there would be any differences in expression depending on whether the cytokine is of human or mouse origin. Would the choice of host strain (BL21 (DE3) vs. BL21 Star™ (DE3)) be affected by the species of the cytokine?
BL21 (DE3) and its variants are designed for expression vectors using the T7 promoter as those strains express the T7 polymerase upon IPTG induction. If you are truly using a plasmid with only the lac promoter then you can use pretty much any host and don't need to use one of the BL21 hosts. There might even be an advantage to not having T7 polymerase present. There are BL21 host strains lacking that, the designation (DE3) means it is carrying a prophage with the T7 polymerase gene on it. So regular BL21 would work fine for you. Whether BL21 or BL21 Star is better can not be predicted in advance, you just need to try.
Having said that, the lac promoter does work fine but it is much lower expressing promoter than many other promoters used for heterologous expression, such as the pQE vectors or the pET vectors. So you are not likely to have high level expression, but it might be enough.
It should not matter whether your gene is mouse or human in origin, both are quite heterologous from E. coli.
Just wanted to add that actually, lac promoter is associated with faster expression than T7 promoterArticle Use of a Transfer-Rna as a Transcriptional Reporter - the T7...
I always used lac/tac promoters for periplasmic expression with Bl21 Gold as a host and it worked great.
Dear Hj Baek
i can be wrong but i do not expect a great difference from BL21(De3) and BL21(DE3)Star. Probably , if you are not using a codon optimized DNA template but a cdna, the use of BL21 (De3) codon plus as well as a Rosetta2 (De3) Strain may improve you expression yield but it is not sure that it may improve the solubility that is more related to other factors.
In my opinion, if you do not need specific labelling (eg 15N, 13C,15N) the best way to produce and purify an human citokine is the use of a mammalian expression sistems as HEK293 or Expi293 those are able to produce all the PTM required. it is certanilly more expensive than E.coli and you need specific instrumentation that you cannot have in an e.coli expression lab.
good luck
Manuele
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