Protein secretion is essential for all organisms. Bacteria have evolved a plethora of secretion systems to handle the various proteins that need to be exported from the cytoplasm. Most of these proteins bear an amino terminal extension termed signal peptide and they are called preproteins. The Sec system is uniquitus and essential for cell viability. In bacteria, the Sec system consists of the membrane embedded heterotrimeric complex SecYEG that forms the channel through which preproteins are threaded and the cytoplasmic nanomotor SecA.
