Tir (receptor)
Encyclopedia
Tir is an essential component in the adherence of the enteropathogenic Escherichia coli
(EPEC) and enterohemorraghic Escherichia coli
to the cells lining the small intestine
. To aid attachment, both EPEC and EHEC possess the ability to reorganise the host cell actin cytoskeleton via the secretion of virulence factors. These factors are secreted directly into the cells using a Type three secretion system
. One of the virulence factors secreted is the Translocated Intimin Receptor (Tir). Tir is a receptor protein encoded by the espE gene which is located on the locus of enterocyte effacement (LEE) pathogenicity island in EPEC strains. It is secreted into the host cell membranes and acts as a receptor for intimin
which is found on the bacterial surface. Once Tir binds intimin, the bacterium is attached to the enterocyte
surface.
Tir is also a receptor tyrosine kinase
(RTK) that initiates its intimate adherence by inserting a hairpin orientation in the intestinal cell membrane to enable tight binding to intimin on the bacterial cell outer membrane. Upon phosphorylation, Tir activates condensation and polymerization of actin
filaments under the bacterial cell to form a pedestal-like structure.
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
(EPEC) and enterohemorraghic Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
to the cells lining the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
. To aid attachment, both EPEC and EHEC possess the ability to reorganise the host cell actin cytoskeleton via the secretion of virulence factors. These factors are secreted directly into the cells using a Type three secretion system
Type three secretion system
Type three secretion system is a protein appendage found in several Gram-negative bacteria....
. One of the virulence factors secreted is the Translocated Intimin Receptor (Tir). Tir is a receptor protein encoded by the espE gene which is located on the locus of enterocyte effacement (LEE) pathogenicity island in EPEC strains. It is secreted into the host cell membranes and acts as a receptor for intimin
Intimin
Intimin is a virulence factor of EPEC and EHEC E. coli strains. It is an attaching and effacing protein which with other virulence factors is responsible for enteropathogenic and enterohaemorrhagic diarrhoea.According to a TIME magazine Q & A story with Martin Wiedmann, a professor of food...
which is found on the bacterial surface. Once Tir binds intimin, the bacterium is attached to the enterocyte
Enterocyte
Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells found in the small intestines and colon. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase surface area for the digestion and transport of molecules from the intestinal...
surface.
Tir is also a receptor tyrosine kinase
Receptor tyrosine kinase
Receptor tyrosine kinases s are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Of the 90 unique tyrosine kinase genes identified in the human genome, 58 encode receptor tyrosine kinase proteins....
(RTK) that initiates its intimate adherence by inserting a hairpin orientation in the intestinal cell membrane to enable tight binding to intimin on the bacterial cell outer membrane. Upon phosphorylation, Tir activates condensation and polymerization of actin
Actin
Actin 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...
filaments under the bacterial cell to form a pedestal-like structure.