Protein folding in the periplasm of Escherichia coli.

With the discovery of molecular chaperones and the development of heterologous gene expression techniques, protein folding in bacteria has come into focus as a potentially limiting factor in expression and as a topic of interest in its own right. Many proteins of importance in biotechnology contain disulphide bonds, which form in the Escherichia coli periplasm, but most work on protein folding in the periplasm of E. coli is very recent and is often speculative. This MicroReview gives a short overview of the possible fates of a periplasmic protein from the moment it is translocated, as well as of the E. coli proteins involved in this process. After an introduction to the specific physiological situation in the periplasm of E. coli, we discuss the proteins that might help other proteins to obtain their correctly folded conformation--disulphide isomerase, rotamase, parts of the translocation apparatus and putative periplasmic chaperones--and briefly cover the guided assembly of multi-subunit structures. Finally, our MicroReview turns to the fate of misfolded proteins: degradation by periplasmic proteases and aggregation phenomena.