31-08-2017, 01:18 PM
N-acyl-L-homoserine lactones (AHL) are co-regulatory ligands necessary for the control of the expression of genes encoding virulence traits in many Gram-negative bacterial species. Recent studies have indicated that AHL modulates the cellular concentrations of LuxR-type regulatory proteins by binding and fortifying these proteins against proteolytic degradation (Zhu and Winans, 2001). Halogenated furanones produced by the macroalga Delisea pulchra inhibit AHL-dependent gene expression. This study tested an in vivo interaction between a tritiated halogenated furanone and the VRB protein of Vibrio fischeri overproduced in Escherichia coli. Although no stable interaction was found between the algae metabolite and the bacterial protein, it was observed by Western analysis that the half-life of the protein is reduced up to 100 fold in the presence of halogenated furanones. This suggests that the halogenated furanones modulate the LuxR activity but act to destabilize, rather than protect, the AHL-dependent transcriptional activator. The furanone-dependent reduction in the cellular concentration of the LuxR protein was associated with a reduction in the expression of a plasmid-encoded P (luxI) -gfp (ASV) fusion, suggesting that the reduction in LuxR concentration is the mechanism by which furanones control the expression of AHL-dependent phenotypes. The mode of action by which the halogenated furanones reduce the cellular concentrations of the LuxR protein remains to be characterized.