title: The chaperone GroESL enhances the accumulation of soluble, active TraR protein, a quorum-sensing transcription factor from Agrobacterium tumefaciens.
abstract: TraR of Agrobacterium tumefaciens is a LuxR-type quorum-sensing transcription factor that regulates genes required for replication and conjugation of the tumor-inducing (Ti) plasmid. TraR requires its cognate autoinducer N-3-oxooctanoyl-homoserine lactone (OOHL) for resistance of proteolysis in wild-type bacteria and for correct protein folding and solubility when overexpressed in E. coli. In this study, we ask whether GroESL might also play a role in TraR folding, as this molecular chaperone assists many proteins in attaining their native tertiary structure. Expression of E. coli GroESL in a strain expressing TraR increases the solubility of TraR and increases transcriptional activity of a TraR-dependent promoter. Both solubility and activity still require OOHL. We also studied the folding of TraR in the closely related bacterium Sinorhizobium meliloti. A mutation in one groEL gene slightly decreased the expression of a TraR-dependent promoter, strongly decreased the accumulation of TraR in Western immunoblot assays, and also strongly influenced the fate of pulse-labeled TraR.
authors.affiliation: Department of Microbiology, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Yunrong
authors.initials: Y
authors.lastname: Chai
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Winans