In addition to the pMAL™ and IMPACT™ expression systems, NEB offers several strains of competent E. coli for protein expression. Depending on your construct, there is a strain of E. coli that will optimally express your desired protein.
- BL21(DE3) Competent E. coli (NEB #C2527), are chemically competent E. coli cells suitable for transformation and routine protein expression. This strain expresses the T7 RNA polymerase and is deficient in proteases Lon and OmpT. These cells are extremely pure and free of animal products.
- Lemo21(DE3) Competent E. coli (NEB #C2528) is a BL21(DE3) strain containing the Lemo System™, offering tunable expression of difficult clones. Tunable expression is achieved by varying the level of lysozyme (lysY), the natural inhibitor of T7 RNA polymerase. The level of lysozyme is modulated by adding L-rhamnose to the expression culture at levels from zero to 2000 µM. When Lemo21(DE3) is grown without rhamnose, the strain performs the same as a pLysS containing strain. However, optional addition of rhamnose tunes the expression of the protein of interest. For difficult soluble proteins, tuning the expression level may also result in more soluble, properly folded protein.
- NiCo21(DE3) Competent E. coli (NEB #C2529) are chemically competent E. coli cells derived from BL21(DE3). Poly-histidine tagged recombinant proteins that are isolated by immobilized metal affinity chromatography (IMAC) are often contaminated with significant amounts of endogenous E. coli metal binding proteins. The protein expression strain NiCo21(DE3) has been engineered to minimize E. coli protein contamination of IMAC fractions: endogenous GlmS is mutated to eliminate binding to IMAC resins and three other proteins (SlyD, ArnA and Can) are tagged to enable rapid removal by chitin affinity chromatography.
- NEB Express Competent E. coli (High Efficiency) (NEB #C2523) are chemically competent E. coli cells suitable for high efficiency transformation and protein expression. They are the recommended host strain for pMAL Protein Fusion and Purification System (NEB #E8200). NEB Express E.coli does not restrict methylated DNA (McrA-, McrBC-, EcoBr-m-, Mrr-). NEB Express Iq Competent E. coli (NEB #C3037) and BL21 Competent E. coli (NEB #C2530) strains may also be used with pMAL vectors or other vectors with a tac, trc, lac, or araBAD promoter.
- The SHuffle® suite of competent E. coli were designed to encourage disulfide bond formation in expressed proteins. Additionally, tight control of expression by lacIq allows for the expression of potentially toxic genes. The SHuffle suite includes SHuffle Express Competent E. coli (NEB #C3028) SHuffle T7 Competent E. coli (NEB #C3026)), SHuffle T7 Express lysY Competent E. coli (NEB #C3030) and SHuffle T7 Express Competent E. coli (NEB #C3029).
- The T7 Express High Efficiency Group of Competent Cells includes four different strains, including T7 Express Iq Competent E. coli (High Efficiency) (NEB#C3016) T7 Express lysY/Iq Competent E. coli (High Efficiency) (NEB #C3013), T7 Express lysY Competent E. coli (High Efficiency) (NEB #C3010) and T7 Express Competent E. coli (High Efficiency) (NEB #C2566). To try the family of T7 Express High Efficiency cells, NEB offers a sampler pack (NEB #C3009). For high efficiency transformation and protein expression for X-ray crystallography, or seleno-methionine labeling of proteins, NEB recommends T7 Express Crystal Competent E. coli (High Efficiency) (NEB #C3022).
pMAL™ and IMPACT™ are trademarks of New England Biolabs, Inc.
Lemo System™ is owned by Xbrane Biosciences AB (Stockholm, Sweden) and has been exclusively licensed to New England Biolabs, Inc. For manufacture and distribution of Lemo21(DE) competent E. coli.
SHuffle® is a registered trademark of New England Biolabs, Inc.