Chaperone competent cells

This product consists of the Escherichia coli strain BL21 transformed by each of five plasmids included in the Chaperone Plasmid Set.

E. coli is commonly used as a host for protein expression because it is the simplest expression system to use and a wide variety of systems are available. However, expression of foreign proteins in E. coli often results in various problems such as formation of inclusion bodies and degradation of expressed protein by protease. These issues often occur as a result of improper folding of the expressed proteins, and are frequently encountered in protein function studies.

Molecular chaperones are known to be involved in the protein folding process, and numerous studies have been conducted to elucidate the mechanisms of in vivo protein folding. The five types of plasmids (pG-KJE8, pGro7, pKJE7, pG-Tf2, pTf16) developed by HSP Research Institute, Inc., are designed to enable efficient expression of multiple molecular chaperones that are known to work in cooperation as a “chaperone team” to facilitate protein folding. It has been reported that coexpression of a target protein with one of these chaperone teams increases recovery of proteins in the soluble fraction; these proteins are often unrecoverable with conventional methods due to the formation of inclusion bodies.

E. coli BL21 is a strain derived from E. coli B, which is deficient in Lon and OmpT (outer membrane) proteases. E. coli BL21 is commonly used for recombinant protein expression because it often results in highly stable expressed protein. Coexpression of a target protein and a chaperone team usually requires three steps: 1. Transform an E. coli host strain with chaperone plasmids; 2. Prepare competent cells using the transformed host strain. 3. Transform these competent cells with a plasmid expressing the target protein. This product, however, only requires one transformation to obtain an E. coli strain that coexpresses the target protein and chaperone team, since it includes competent cells prepared from a BL21 strain already transformed by chaperone plasmids. In addition to the competent cells containing the five types of plasmids, competent BL21 cells that do not contain any chaperone plasmids are also available for use as a control.

Each competent cell line is prepared from E. coli BL21 transformed with one of the chaperone plasmids. The competent cell sets are useful for protein expression with the pCold DNA series. This product is not intended for protein expression systems utilizing a T7 promoter, such as the pET system, because these BL21 host strains do not express T7 RNA polymerases.