Bacterial protein secretion

Bacterial protein secretion is the microbiological term for the excretion of various proteins by many bacteria into the surrounding medium . Enzymes and bacterial toxins are among the most important proteins excreted. The transport takes place depending on the Sec system through the cytoplasmic membrane or independently of the Sec system. Because of their additional outer membrane, Gram-negative bacteria require more complex excretion systems than Gram-positive bacteria.

Gram negative bacteria

Entire secretion system in Gram-negative bacteria.

So far, six types (type I to type VI) of secretion systems are known in Gram-negative bacteria, two of which use the Sec system.

Type I.

Prototype is the Escherichia coli - hemolysin Transport System. Three membrane proteins allow Sec-independent secretion in one step.

Type II

Type II secretion route

Prototype is the Klebsiella - pullulanase secretion system. A large number of proteins form a transport complex with a pore in the outer membrane. Transport takes place in two steps, the first step being through the cytoplasmic membrane Sec -dependent or Tat -dependent.

Type III

→ Main article : Type III secretion system

The prototype is the Yersinia- Yop system. A multitude of proteins form a needle structure that protrudes from the cytoplasm through both membranes. Proteins are transported Sec-independently in one step. Type III systems are partially activated by contact with target cells and also allow proteins to be injected into the target cell.

Type IV

The prototype is the Vir system from Agrobacterium tumefaciens . A large number of proteins form a complex that protrudes through both membranes. Proteins are transported Sec-independently in one step. Some type IV systems allow injection of proteins into the target cell after contact with target cells. Some type IV systems carry proteins and DNA .

Type V (car transporter)

Prototype is the IgA - protease from Neisseria . The type V secretion system comprises proteins which, as autotransporters, contain all the information required for translocation across the cell membrane in the polypeptide chain itself. The proteins are sec-dependent secreted into the periplasm via the cytoplasmic membrane . A domain at the C-terminal end of the protein integrates into the outer membrane and transports the protein to the outside, where it is proteolytically cut off.

Type VI

A large number of proteins form a complex that protrudes through both membranes. Proteins are transported Sec-independently in one step. The type VI system allows proteins to be injected into the target cell after contact with target cells.

Gram positive bacteria

Entire secretion system in Gram-positive bacteria.

This secretion system is not as complex as that of the Gram-negative bacteria, as only one membrane has to be crossed. The Sec-System or the Tat-System is often used to transport proteins across the individual membrane.

Injectosome

A protein transported to the outside via the Sec system can be transported into the target cell via the injectosome.

Special proteins

Fimbrillin proteins are transported across the membrane via the FPE (fimbrillin protein exporter) and flagella by the FEA (flagella export apparatus).

Type VII

The system occurs in mycobacteria and corynebacteria , which have a slightly different lipid composition in their membrane, the so-called mycomembrane. Some proteins form a complex that penetrates the membrane to the outside. Proteins are transported Sec-independently in one step. The Type VII system allows proteins to be injected into the target cell after contact with target cells.

literature

• Michael T. Madigan, John M. Martinko, Jack Parker: Brock Microbiology. German translation edited by Werner Goebel, 1st edition. Spektrum Akademischer Verlag GmbH, Heidelberg / Berlin 2000, ISBN 978-3-8274-0566-1 .
• Meißner, D .: Comparative analysis of Sec- and Tat-dependent secretory protein production with Gram-positive bacteria as host organisms. Writings of the Forschungszentrum Jülich series Lebenswissenschaften / Life Sciences, Volume 26. Forschungszentrum Jülich 2006. ISBN 3-89336-427-7 .
• Green, E., Mecsas, J .: Bacterial Secretion Systems - An overview . Ed .: Microbiology Spectrum. Boston February 4, 2016, doi : 10.1128 / microbiolspec.VMBF-0012-2015 .