4 - Protein Export in Bacteria

Abstract

This chapter provides an explanation about the protein export in bacteria. The cytoplasmic membrane of bacteria is the site for energy-transducing processes such as respiration, ATP synthesis, solute transport, and flagellar movement. The molecular mechanism of bacterial protein export has been studied in great detail during the last two decades using the powerful genetic and biochemical tools that are available for E. coli. General chaperones such as GroEL and DnaK can substitute for SecB in stabilizing preproteins in a translocation competent state, but they cannot substitute for the specific targeting function of SecB in protein export. The interaction between SecA and the major channel subunit SecY involves multiple regions of both proteins. The actual protein-conducting channel is lined up by four SecYEG complexes. The latter is not essential for translocation, and although it may be functionally homologous, it is not similar to the bacterial SecG. The mechanism underlying thermal sensitivity of protein export is not known, but potential cold-sensitive steps could be insertion of the signal sequence and/or SecA into the membrane, or the oligomerization of the SecYEG complex into a protein-conducting channel. Finally on a concluding note, this chapter summarizes three historical notes as well.