Ejectosome
Encyclopedia
An ejectosome is a cellular organelle
responsible for ejecting their contents from the cell. Two unrelated types of ejectosomes are described in the literature:
Cryptomonad
ejectosomes contain two connected spiral ribbon-like structures, held under tension. If the cells are irritated either by mechanical, chemical or light stress, they discharge, propelling the cell in a zig-zag course away from the disturbance. Large ejectisomes, visible under the light microscope, are associated with the pocket; smaller ones occur elsewhere on the cell.
Mycobacteria are ejected from host cells through the action of an actin-based ejectosome. This escape mechanism requires a cytoskeleton
regulator from the host plus an intact mycobacterial ESX-1 secretion
system. Ejectosomes apparently exert a contractile force, forming a tight septum around the bacteria. Ejection of the bacteria occurs without host cell lysis.
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
responsible for ejecting their contents from the cell. Two unrelated types of ejectosomes are described in the literature:
- CryptomonadCryptomonadThe cryptomonads are a group of algae, most of which have plastids. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10-50 μm in size and flattened in shape, with an anterior groove or pocket...
s have two types of characteristic ejectisomes known as extrusomes. - IntracellularIntracellularNot to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...
pathogenPathogenA pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s, such as Mycobacterium tuberculosisMycobacterium tuberculosisMycobacterium tuberculosis is a pathogenic bacterial species in the genus Mycobacterium and the causative agent of most cases of tuberculosis . First discovered in 1882 by Robert Koch, M...
, escape from their host cells using an actinActinActin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
-based structure, also called an ejectosome.
Cryptomonad
Cryptomonad
The cryptomonads are a group of algae, most of which have plastids. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10-50 μm in size and flattened in shape, with an anterior groove or pocket...
ejectosomes contain two connected spiral ribbon-like structures, held under tension. If the cells are irritated either by mechanical, chemical or light stress, they discharge, propelling the cell in a zig-zag course away from the disturbance. Large ejectisomes, visible under the light microscope, are associated with the pocket; smaller ones occur elsewhere on the cell.
Mycobacteria are ejected from host cells through the action of an actin-based ejectosome. This escape mechanism requires a cytoskeleton
Cytoskeleton
The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within a cell's cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton...
regulator from the host plus an intact mycobacterial ESX-1 secretion
Secretion
Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
system. Ejectosomes apparently exert a contractile force, forming a tight septum around the bacteria. Ejection of the bacteria occurs without host cell lysis.