Recommended E. coli Expression Vectors and Competent Strains

1. Recommended E. coli Expression Vectors

1. pET-28a: T7 promoter with a 6×His purification tag, making it a widely used vector for recombinant protein expression and purification.

2. pET-32a: T7 promoter with a 6×His purification tag and a TrxA solubility-enhancing tag, which can help improve the soluble expression of recombinant proteins.

3. pGEX4T-1: Tac promoter with a GST fusion tag that can facilitate both protein purification and solubility.

4. pET28a-SUMO: T7 promoter with a 6×His purification tag and a SUMO solubility-enhancing tag, suitable for improving the soluble expression of challenging recombinant proteins.

5. pCold-SUMO: A cold-shock-inducible expression vector with a 6×His purification tag and a SUMO solubility-enhancing tag, suitable for recombinant protein expression at lower temperatures.

6. pUC19-pJ23119-MCS: A constitutive expression vector for continuous expression without the need for induction.

7. pET28a-EGFP: An EGFP expression plasmid that can be used as a positive control for protein expression and fluorescence detection.

2. Recommended E. coli Expression Strains

1. BL21(DE3): A widely used expression strain for high-level production of non-toxic recombinant proteins.

2. BL21(DE3)pLysS: Suitable for expressing potentially toxic proteins. The additional T7 lysozyme helps reduce basal expression from the T7 promoter.

3. BL21-CodonPlus(DE3)-RIPL: Designed to improve the expression of recombinant proteins containing codons that are rarely used in E. coli by providing additional tRNAs for rare codons.

4. Rosetta(DE3): Supplies additional tRNAs for several rare codons that are underrepresented in E. coli, helping improve the expression of heterologous proteins.

5. OrigamiB(DE3): Provides a more oxidizing cytoplasmic environment, which can facilitate the formation of disulfide bonds and improve the folding of recombinant proteins containing disulfide bonds.

6. ArcticExpress(DE3)RP: Co-expresses cold-adapted chaperonins, helping promote proper protein folding and improve soluble expression at lower temperatures.

7. Shuffle T7: A specialized E. coli expression strain designed to promote correct disulfide bond formation and protein folding, making it particularly useful for recombinant proteins containing multiple disulfide bonds.

How to Choose an E. coli Expression System

The choice of an E. coli expression system depends largely on the protein's toxicity, solubility, folding requirements, and codon usage.

For routine expression of non-toxic proteins, pET-28a with BL21(DE3) is a common starting point. For proteins with poor solubility, fusion tags such as TrxA, SUMO, or GST may help improve soluble expression.

For proteins containing many rare codons, Rosetta(DE3) or BL21-CodonPlus(DE3)-RIPL may be more suitable. For proteins that require disulfide bond formation, strains such as OrigamiB(DE3) or Shuffle T7 can be considered.

Choosing an appropriate combination of expression vector + E. coli host strain + induction conditions can significantly improve recombinant protein expression and downstream purification.

For more information about E. coli expression plasmids and related products, please contact MiaoLingBio.