Rhs toxins belong to the polymorphic toxin category of bacterial exotoxins. [1] Rhs proteins are widespread and can be produced by both Gram-negative and Gram-positive bacteria. [2] Rhs toxins are very large proteins of usually more than 1,500 aminoacids with variable C-terminal toxic domains. Their toxic activity can either target eukaryotes or other bacteria.
In their large N-terminal region, Rhs toxins comprise RHS/YD repeats in various number (PF05593) (RHS meaning Rearrangement Hot Spot) [3] and another "RHS-repeats associated core" domain (PF03527). In contrast, their C-terminal regions are shorter and harbor highly variable C-terminal domains including many domains with a predicted nuclease activity. [2]
These toxins encompass Rhs toxins of insect pathogens with an activity against insects. [4] This group also include Rhs toxins with an activity against human phagocytic cells that contribute to pathogenesis of Pseudomonas aeruginosa . [5]
A role in inter-bacterial competition has been demonstrated for the plant pathogen Dickeya dadantii and for the human pathogen Escherichia coli . [6] [7]
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. [1]
Some Rhs toxins such as the previously mentioned system in Dickeya dadantii appear to be dependent on the type VI secretion system for delivery into neighbouring cells. [6] 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. [8] The C-terminal toxins of Rhs may vary to diversify the antimicrobial activity of the type VI secretion system. [7]