Autoinducer synthase (IPR001690)

Short name: Autoind_synthase

Overlapping homologous superfamilies

Family relationships



Bacterial species have many methods of controlling gene expression and cell growth. Regulation of gene expression in response to changes in cell density is termed quorum sensing [PMID: 10607620, PMID: 9990077]. Quorum-sensing bacteria produce, release and respond to hormone-like molecules (autoinducers) that accumulate in the external environment as the cell population grows. Once a threshold of these molecules is reached, a signal transduction cascade is triggered that ultimately leads to behavioural changes in the bacterium [PMID: 9990077]. Autoinducers are thus clearly important mediators of molecular communication.

Conjugal transfer of Agrobacterium octopine-type Ti plasmids is activated by octopine, a metabolite released from plant tumours [PMID: 8188582]. Octopine causes conjugal donors to secrete a pheromone, Agrobacterium autoinducer (AAI), and exogenous AAI further stimulates conjugation. The putative AAI synthase and an AAI-responsive transcriptional regulator have been found to be encoded by the Ti plasmid traI and traR genes, respectively. TraR and TraI are similar to the LuxR and LuxI regulatory proteins of Vibrio fischeri, and AAI is similar in structure to the diffusable V. fischeri autoinducer, the inducing ligand of LuxR. TraR activates target genes in the presence of AAI and also activates traR and traI themselves, creating two positive-feedback loops. TraR-AAI-mediated activation in wild-type Agrobacterium strains is enhanced by culturing on solid media, suggesting a possible role in cell density sensing [PMID: 8188582].

Production of light by the marine bacterium V. fischeri and by recombinant hosts containing cloned lux genes is controlled by the density of the culture [PMID: 3697093]. Density-dependent regulation of lux gene expression has been shown to require a locus consisting of the luxR and luxI genes.

In these and other Gram-negative bacteria, N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) acts as the autoinducer by binding to transcriptional regulatory proteins and activating them [PMID: 7968529]. OHHL and related molecules, such as N-butanoyl- (BHL), N-hexanoyl- (HHL) and N-oxododecanoyl- (PAI) homoserine lactones, are produced by a family of proteins that share a high level of sequence similarity.

Proteins which currently members of this family include:

  • luxI from V. fischeri.
  • ahyI and asaI from Aeromonas species, which synthesize BHL and whose targets are ahyR and asaR respectively.
  • carI from Erwinia carotovora. The target of OHHL is carR which activates genes involved in the biosynthesis of carbapenem antibiotics.
  • eagI from Enterobacter agglomerans. The target of OHHL is not yet known.
  • esaI from Erwinia stewartii.
  • expI from Erwinia carotovora.
  • lasI from Pseudomonas aeruginosa, which synthesizes PAI and whose target is lasR which activates the transcription of the elastase gene.
  • rhlI (or vsmI) from P. aeruginosa, which synthesizes BHL and HHL and whose target is rhlR.
  • swrI from Serratia liquefaciens, which synthesizes BHL.
  • yenI from Yersinia enterocolitica.

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0016740 transferase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles