Tir (translocated intimin receptor) is an essential component in the adherence of the enteropathogenic ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

'' (EPEC) and enterohemorraghic ''

'' (EHEC) to the cells lining the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

. 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 (often written Type III secretion system and abbreviated TTSS or T3SS, also called Injectisome) is a protein appendage found in several Gram-negative bacteria. In pathogenic bacteria, the needle-like structure is used ...

. 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 is a virulence factor ( adhesin) of EPEC (''e.g.'' ''E. coli'' O127:H6) and EHEC (''e.g. E. coli'' O157:H7) ''E. coli'' strains. It is an attaching and effacing (A/E) protein, which with other virulence factors is necessary and responsi ...

which is found on the bacterial surface. Once Tir binds intimin, the bacterium is attached to the

enterocyte Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells which line the inner surface of the small and large intestines. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase its ...

surface. Tir is also a

receptor tyrosine kinase Receptor tyrosine kinases (RTKs) 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 ...

(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 is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of over ...

filaments under the bacterial cell to form a pedestal-like structure.

References

{{Portal bar, Biology, border=no Enterobacteria Tyrosine kinase receptors