Envelope Spanning Secretion Systems in Gram-negative Bacteria
Matthias J Brunner, Rémi Fronzes and Thomas C Marlovits
from: Bacterial Membranes: Structural and Molecular Biology (Edited by: Han Remaut and Rémi Fronzes). Caister Academic Press, U.K. (2014)
Gram-negative bacteria have a cell envelope made of two membranes separated by a thin layer of peptidoglycan. To transport macromolecules such as proteins and DNA through the entire cell envelope, several types of secretion systems are employed. This chapter focuses on the structure and function of type III and type IV secretion systems. Type III secretion (T3S) systems are used by pathogens such as Salmonella, Shigella and Yersinia. They are composed of more than 20 different proteins, some of them present in multiple copies. Their function is to inject proteinaceous toxins, referred to as "effectors", into the eukaryotic host cell upon intimate contact. One pathogen typically secrets many different effectors-most of them have in common that they hijack part of the host cell machinery. Type IV secretion (T4S) systems are versatile secretion systems found in many bacteria. Typical T4S systems are made of 12 different proteins. Within the T4S family, three groups can be defined: First, T4S systems that mediate conjugative transfer of mobile genetic elements into a wide range of bacterial species but also into eukaryotic cells. Second, type IV secretion systems mediating DNA uptake or release from or into the extracellular milieu. And third, type IV secretion systems directly involved in virulence, secreting virulence factors into mammalian host cells. These are used by pathogens such as Helicobacter pylori or Legionella pneumophila read more ...