SHuffle^® strains for the expression of multi-disulfide bonded and difficult-to-express proteins

Disulfide bonds are covalent bonds formed post-translationally by the oxidation of a pair of cysteines. Disulfide bonds can greatly increase the stability of a protein, and are mostly found in proteins that reside outside the chaperone-rich, protective environment of the cytoplasm (e.g., secreted peptides, hormones, antibodies, interferons, scavenging enzymes, etc.). [see animation 1 of 4, at right] Disulfide bonds can also serve catalytic (e.g., oxidoreductases) and signaling roles (e.g., oxidative stress response).

The redox state of the cytoplasm of eukaryotic and prokaryotic cells is reducing, due to the presence of numerous disulfide bond reductases, such as thioredoxins and glutaredoxins. As such, any disulfide bond formed between two cysteines will quickly and efficiently be reduced back to its thiolate state. To form stable disulfide bonds within proteins, disulfide bond formation is typically compartmentalized outside of the reducing cytoplasm. [see animation 2 of 4, at right] In eukaryotes, disulfide bond formation is catalyzed by Protein Disulfide Bond Isomerase (PDI) in the endoplasmic reticulum (ER), whereas in prokaryotes, disulfide bond formation is catalyzed by DsbA in the periplasm. [see animation 3 of 4, at right] An inherent problem in the process of disulfide bond formation is mis-pairing (mis-oxidation) of cysteines, which can cause misfolding, aggregation and, ultimately, result in low yields during protein production. Proteins that are mis-oxidized must be repaired and disulfide bonds must be shuffled back to their correctly oxidized native state. This is achieved by PDI in eukaryotes and DsbC by prokaryotes.

There are several options for expressing proteins that require disulfide bonding for proper folding and function. The E. coli strain SHuffle® has been genetically engineered for the cytoplasmic production of disulfide-bonded proteins. Genetic deletion of the two (glutaredoxin and thioredoxin) reducing pathways in E. coli has resulted in a mutant strain with diminished capacity to reduce proteins, and an increased capacity to oxidize cytoplasmically-expressed proteins. Additionally, these cells have been engineered to express the disulfide bond isomerase DsbC in the cytoplasm, further enhancing the capacity for and fidelity of disulfide bond formation in this host. [see animation 4 of 4, at right]

Strain	NEB #	Characteristics	Drug Resistance
SHuffle Express Competent E. coli	C3028	Protease Deficient B Strains	Spec
SHuffle T7 Express Competent E. coli	C3029	Protease Deficient B Strains T7 Expression	Spec*
SHuffle T7 Express lysY Competent E. coli	C3030	Protease Deficient B Strains T7 Expression Tight control/expression of toxic proteins	Cam, Spec*
SHuffle T7 Competent E. coli	C3026	K12 Strains T7 Expression	Str, Spec

* Resistance to low levels of steptomycin may be observed.

It is also possible to use eukaryotic protein secretion or cell-free expression strategies to achieve proper disulfide bonding of proteins. For example, secretion of a target protein into the oxidative ER environment of yeast, mammalian or insect cells will permit a nascent protein the opportunity to fold in and to have access to PDI. Cell-free strategies can also be employed using systems like PURExpress^® with Disulfide Bond Enhancer that contains components that improve in vitro formation of disulfide bonds.

NEB offers SHuffle strains for the expression of multi-disulfide bonded and difficult-to-express proteins.