Rhs toxins belong to the polymorphic toxin category of bacterial

exotoxin An exotoxin is a toxin secreted by bacteria. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host. Exotoxins may be secreted, or, simi ...

s. Rhs proteins are widespread and can be produced by both

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

and

Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. Rhs toxins are very large proteins of usually more than 1,500

aminoacids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ami ...

with variable

C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...

toxic domains. Their toxic activity can either target

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

s or other

Domain architecture

In their large

N-terminal The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide, referring to the free amine group (-NH2) located at the end of a polypeptide. Within a peptide, the ami ...

region, Rhs toxins comprise RHS/YD repeats in various number
PF05593
(RHS meaning Rearrangement Hot Spot) and another "RHS-repeats associated core" domain
PF03527
. In contrast, their

regions are shorter and harbor highly variable

domains including many domains with a predicted

nuclease A nuclease (also archaically known as nucleodepolymerase or polynucleotidase) is an enzyme capable of cleaving the phosphodiester bonds between nucleotides of nucleic acids. Nucleases variously effect single and double stranded breaks in their ta ...

activity.

Function

Anti-eukaryotic activity

These toxins encompass Rhs toxins of insect pathogens with an activity against insects. This group also include Rhs toxins with an activity against human

phagocytic Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...

cells that contribute to

pathogenesis Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...

of ''

Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic–facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. aerugi ...

''.

Anti-bacterial activity

A role in inter-bacterial competition has been demonstrated for the plant pathogen ''

Dickeya dadantii ''Dickeya dadantii'' is a gram-negative bacillus that belongs to the family Pectobacteriaceae. It was formerly known as ''Erwinia chrysanthemi'' but was reassigned as ''Dickeya dadantii'' in 2005. Members of this family are facultative anaerobe ...

'' and for the human pathogen ''

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 ...

''. When a polymorphic toxin with anti-bacterial activity is produced by a bacterial strain, this strain is protected by a specific immunity protein encoded by a gene immediately downstream of the toxin gene.

Delivery

Some Rhs toxins such as the previously mentioned system in ''Dickeya dadantii'' appear to be dependent on the

type VI secretion system The type VI secretion system (T6SS) is molecular machine used by a wide range of Gram-negative bacterial species to transport effectors from the interior (cytoplasm or cytosol) of a bacterial cell across the cellular envelope into an adjacent targe ...

for delivery into neighbouring cells. PAAR domain toxins such as Rhs appear to form the sharp tip of the type VI secretion system being attached to the VgrG of the secretion apparatus. The C-terminal toxins of Rhs may vary to diversify the antimicrobial activity of the type VI secretion system.

References

{{Reflist, 32em

External links

Rhs proteins in the InterPro database
Bacterial toxins