Shiga-like toxin
Encyclopedia
Shiga-like toxin, also known as verotoxin, is a toxin generated by some strains of Escherichia coli (but see below). It is named for its similarity to the AB5-type
Shiga toxin
produced by the bacteria
Shigella dysenteriae
.
There are two types, known as SLT1 and SLT2.
s on the cells' surface in order to attach and enter the cell
; species
such as cattle
, swine, and deer
which do not carry these receptors may harbor toxigenic bacteria without any ill effect, shedding them in their feces
, from where they may be spread to humans.
known as Gb3. Binding of the subunit B to Gb3 causes induction of narrow tubular membrane invaginations, which drives formation of inward membrane tubules for the bacterial uptake into the cell. These tubules are essential for uptake into the host cell. When the protein is inside the cell, the A subunit interacts with the ribosome
s to inactivate them. The A subunit of Shiga toxin is an N-glycosidase that modifies the RNA
component of the ribosome to inactivate it and so bring a halt to protein synthesis leading to the death of the cell. The vascular endothelium has to continually renew itself, so this killing of cells leads to a breakdown of the lining and to hemorrhage. The first response is commonly a bloody diarrhea. This is because Shiga toxin is usually taken in with contaminated food
or water
.
The toxin is effective against small blood vessels, such as found in the digestive tract, the kidney
, and lungs, but not against large vessels such as the arteries or major veins. A specific target for the toxin appears to the vascular endothelium of the glomerulus
. This is the filtering structure that is a key to the function of the kidney. Destroying these structures leads to kidney failure and the development of the often deadly and frequently debilitating hemolytic uremic syndrome. Food poisoning with Shiga toxin often also has effects on the lungs and the nervous system
.
lambdoid prophage
, such as H-19B or 933W, inserted into the bacteria's
chromosome
via transduction
.
AB5 toxin
The AB5 toxins are six-component protein complexes secreted by a number of pathogenic bacteria. All share a similar structure and mechanism for entering targeted host cells.- Structure and mechanism :...
Shiga toxin
Shiga toxin
Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, whose genes are considered to be part of the genome of lambdoid prophages. The toxins are named for Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae. The most common...
produced by the bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
Shigella dysenteriae
Shigella dysenteriae
Shigella dysenteriae is a species of the rod-shaped bacterial genus Shigella. Shigella can cause shigellosis . Shigellae are Gram-negative, non-spore-forming, facultatively anaerobic, non-motile bacteria.S...
.
There are two types, known as SLT1 and SLT2.
Transmission
As with Shiga toxin, the toxin requires highly specific receptorReceptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
s on the cells' surface in order to attach and enter the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
; species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
such as cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
, swine, and deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
which do not carry these receptors may harbor toxigenic bacteria without any ill effect, shedding them in their feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
, from where they may be spread to humans.
Structure and mechanism
Mechanism of action
The toxin acts on the lining of the blood vessels, the vascular endothelium. The B subunits of the toxin bind to a component of the cell membraneCell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
known as Gb3. Binding of the subunit B to Gb3 causes induction of narrow tubular membrane invaginations, which drives formation of inward membrane tubules for the bacterial uptake into the cell. These tubules are essential for uptake into the host cell. When the protein is inside the cell, the A subunit interacts with the ribosome
Ribosome
A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
s to inactivate them. The A subunit of Shiga toxin is an N-glycosidase that modifies the RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
component of the ribosome to inactivate it and so bring a halt to protein synthesis leading to the death of the cell. The vascular endothelium has to continually renew itself, so this killing of cells leads to a breakdown of the lining and to hemorrhage. The first response is commonly a bloody diarrhea. This is because Shiga toxin is usually taken in with contaminated food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
or water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
.
The toxin is effective against small blood vessels, such as found in the digestive tract, the kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
, and lungs, but not against large vessels such as the arteries or major veins. A specific target for the toxin appears to the vascular endothelium of the glomerulus
Glomerulus
A glomerulus is a capillary tuft that is involved in the first step of filtering blood to form urine.A glomerulus is surrounded by Bowman's capsule, the beginning component of nephrons in the vertebrate kidney. A glomerulus receives its blood supply from an afferent arteriole of the renal...
. This is the filtering structure that is a key to the function of the kidney. Destroying these structures leads to kidney failure and the development of the often deadly and frequently debilitating hemolytic uremic syndrome. Food poisoning with Shiga toxin often also has effects on the lungs and the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
.
Source of toxin gene
It has been suggested by some researchers that the gene coding for Shiga-like toxin comes from a toxin-convertinglambdoid prophage
Prophage
A prophage is a phage genome inserted and integrated into the circular bacterial DNA chromosome. A prophage, also known as a temperate phage, is any virus in the lysogenic cycle; it is integrated into the host chromosome or exists as an extrachromosomal plasmid. Technically, a virus may be called...
, such as H-19B or 933W, inserted into the bacteria's
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
via transduction
Transduction (genetics)
Transduction is the process by which DNA is transferred from one bacterium to another by a virus. It also refers to the process whereby foreign DNA is introduced into another cell via a viral vector. Transduction does not require cell-to-cell contact , and it is DNAase resistant...
.
See also
- Escherichia coli O157:H7Escherichia coli O157:H7Escherichia coli O157:H7 is an enterohemorrhagic strain of the bacterium Escherichia coli and a cause of foodborne illness. Infection often leads to hemorrhagic diarrhea, and occasionally to kidney failure, especially in young children and elderly persons...
- Escherichia coli O104:H4Escherichia coli O104:H4Escherichia coli O104:H4 is a rare enterohemorrhagic strain of the bacterium Escherichia coli, and the cause of the 2011 Escherichia coli O104:H4 outbreak...
- Hemolytic-uremic syndromeHemolytic-uremic syndromeHemolytic-uremic syndrome , abbreviated HUS, is a disease characterized by hemolytic anemia, acute renal failure and a low platelet count . It predominantly, but not exclusively, affects children. Most cases are preceded by an episode of diarrhea caused by E. coli O157:H7, which is acquired as a...
External links
- http://www.textbookofbacteriology.net/Shigella.html
- http://www.textbookofbacteriology.net/Shigella.html
- http://dnaresearch.oxfordjournals.org/cgi/reprint/6/2/141?ck=nck