Hello

Kindly look at links here 

Good Luck 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4240710/

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2010000100005

http://discovery.ucl.ac.uk/1381835/1/DaSilvaMetelo_PhDThesis.pdf

These links may help you

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3178102/

https://www.ncbi.nlm.nih.gov/pubmed/26742898

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2771296/

https://www.ncbi.nlm.nih.gov/pubmed/21843625

https://www.embl.de/pepcore/pepcore_services/protein_expression/ecoli/

https://www.genscript.com/technical-guide.html

Good Luck

HI

Expression depends on many factor.

You do not mentioned even your vector or your host!!!!

How can we help you?

Get a good optimization protocol, such as those mentioned above. You may end up trying a pretty wide variety of variables, including constructs/purification tags/solubility tags/placement of tags/salts/media/temperature/inducing agent amounts/cofactors/additives/glycerol/etc.

The list can get pretty extensive and could be nearly impossible without knowing more about your current setup. Which plasmid do you have it in and which expression cell line are you using?

I have tried different vectors like pET42, pET28a and pET44 using either BL21(DE3) or Rosetta cells. I even HMS 174 cells at point. The pET44 showed a bit improved expression but not enough to purify.

Hi Collins,

I fear that you are going to find it very difficult to express this in E. coli. CD18 in particular is a heavily disulfide bonded protein (for example, the structure 5E6X, which is just a fragment of the integrin, has at least six disulfides from a very casual glance). Disulfides do not form in the E. coli cytosol unless you use a strain like the Origami strains - and even then, getting so many to form correctly is highly unlikely. Periplasmic expression is another option, but again I would be very skeptical about the chances of getting such a challenging protein soluble in E. coli. The protein also has multiple glycosylation sites, and it is likely that at partly this supports solubility.

From reading the paper about 5E6X (http://www.pnas.org/content/113/11/2940.full), this was expressed in HEK293 cells. My suspicion is that you would need to go to at least insect cells, and very possibly mammalian cells, to get proper expression and post-translational processing of these very challenging biomolecules.

Probably not what you wanted to hear, but unfortunately this is most likely reality.

I completely agree with Nicholas above. 

You could try yeast or insect cells, but it would very possibly end up being a waste of time with how many post-translational modifications it sounds like your protein has. Not sure Origami cells or periplasmic expression is going to get you anywhere near what your protein requires, either. 

Do you have tissue culture lab capabilities to express in mammalian cells? If not, I think insect might be your best option.