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Type three secretion system (often written Type III secretion system and abbreviated TTSS or T3SS, also called Injectisome or Injectosome) is a protein appendage found in several Gram-negative bacteria. In pathogenic bacteria, the needle-like structure is used as a sensory probe to detect the presence of eukaryotic organisms and secrete proteins that help the bacteria infect them. The secreted effector proteins are secreted directly from the bacterial cell into the eukaryotic (host) cell, where they exert a number of effects that help the pathogen to survive and to escape an immune response. == Overview == The term Type III secretion system was coined in 1993. This secretion system is distinguished from at least five other secretion systems found in Gram-negative bacteria. Many bacteria possess a T3SS and can transfer the T3SS gene cassette horizontally to other species. The most researched T3SSs are from species of ''Shigella'' (causes bacillary dysentery), ''Salmonella'' (typhoid fever), ''Escherichia coli'' (Gut flora, some strains cause food poisoning), ''Vibrio'' (gastroenteritis and diarrhea), ''Burkholderia'' (glanders), ''Yersinia'' (plague), ''Chlamydia'' (sexually transmitted disease), ''Pseudomonas'' (infects humans, animals and plants) and the plant pathogens ''Erwinia'', ''Ralstonia'' and ''Xanthomonas'', and the plant symbiont ''Rhizobium''. The T3SS is composed of approximately 30 different proteins, making it one of the most complex secretion systems. Its structure shows many similarities with bacterial flagella (long, rigid, extracellular structures used for motility). Some of the proteins participating in T3SS share amino-acid sequence homology to flagellar proteins. Some of the bacteria possessing a T3SS have flagella as well and are motile (''Salmonella'', for instance), and some do not (''Shigella'', for instance). Technically speaking, type III secretion is used both for secreting infection-related proteins and flagellar components. However, the term "type III secretion" is used mainly in relation to the infection apparatus. The bacterial flagellum shares a common ancestor with the type III secretion system. T3SSs are essential for the pathogenicity (the ability to infect) of many pathogenic bacteria. Defects in the T3SS may render a bacterium non-pathogenic. It has been suggested that some non-invasive strains of gram-negative bacteria have lost the T3SS because the energetically costly system is no longer of use. Although traditional antibiotics were effective against these bacteria in the past, antibiotic-resistant strains constantly emerge. Understanding the way the T3SS works and developing drugs targeting it specifically have become an important goal of many research groups around the world since the late 1990s. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Type three secretion system」の詳細全文を読む スポンサード リンク
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