Substrate specificity and function of the pheromone receptor AinR in Vibrio fischeri ES114.
Two distinct but interrelated pheromone-signaling systems, LuxI/LuxR and AinS/AinR, positively control bioluminescence in Vibrio fischeri. Although each system generates an acyl-homoserine lactone (AHL) signal, the protein sequences of LuxI/LuxR and AinS/AinR are unrelated. AinS and LuxI generate the pheromones N-octanoyl-AHL (C8-AHL) and N-3-oxo-hexanoyl-AHL (3OC6-AHL), respectively. LuxR is a transcriptional activator that responds to 3OC6-AHL, and to a lesser extent to C8-AHL. AinR is hypothesized to respond to C8-AHL and, based on homology to Vibrio harveyi LuxN, to mediate the repression of a Qrr regulatory RNA. However, a ΔainR mutation decreased luminescence, which was not predicted based on V. harveyi LuxN, raising the possibility of a distinct regulatory mechanism for AinR. Here we show that ainR can complement a luxN mutant, suggesting functional similarity. Moreover, in V. fischeri, we observed ainR-dependent repression of a Pqrr-lacZ transcriptional reporter in the presence of C8-AHL, consistent with its hypothesized regulatory role. The system appears quite sensitive, with a half-maximal effect on a Pqrr reporter at 140 pM C8-AHL. Several other AHLs with substituted and unsubstituted acyl chains between 6 and 10 carbons also displayed an AinR-dependent effect on Pqrr-lacZ; however, AHLs with acyl chains of four carbons or 12 or more carbons lacked activity. Interestingly, 3OC6-AHL also affected expression from the qrr promoter, but this effect was largely luxR dependent, indicating a previously unknown connection between these systems. Finally, we propose a preliminary explanation for the unexpected luminescence phenotype of the ΔainR mutant.
Department of Microbiology, University of Georgia, Athens, Georgia, USA.
John H
JH
Kimbrough
Eric V
EV
Stabb
D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000378:metabolism; D048908:Aliivibrio fischeri / Q000378:metabolism / Q000502:physiology*; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D006714:Homoserine / Q000031:analogs & derivatives / Q000378:metabolism; D007783:Lactones / Q000378:metabolism; D043563:Receptors, Pheromone / Q000378:metabolism*; D015398:Signal Transduction; D013379:Substrate Specificity; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
C096877:AinR protein, Vibrio fischeri; D001426:Bacterial Proteins; D007783:Lactones; C091088:N-octanoylhomoserine lactone; D043563:Receptors, Pheromone; D006714:Homoserine; C030654:N-(3-oxohexanoyl)-3-aminodihydro-2(3H)-furanone; D001616:beta-Galactosidase; D015107:4-Butyrolactone